College Level Meteorology

Meteorology

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CONTENTS Preface........................................................................................................ 1 Chapter 1: Understanding the Earth's Atmosphere ..................................... 1 Early Atmosphere on Earth ............................................................................................. 1 What is the Atmosphere made of? ................................................................................... 3 Atmospheric Layers ......................................................................................................... 4 Troposphere.................................................................................................................. 6 Stratosphere ................................................................................................................. 6 Mesosphere................................................................................................................... 7 Thermosphere .............................................................................................................. 7 Exosphere ..................................................................................................................... 7 Other Layer Types ........................................................................................................ 8 Longitude and Latitude ................................................................................................... 9 Measuring Air Pressure and Density .............................................................................. 11 Measuring Barometric Pressure .................................................................................... 12 Air Density ..................................................................................................................... 15 Key Points in This Chapter ............................................................................................ 16 Chapter One: Questions ..................................................................................................17 Chapter 2: Cooling and Warming the Earth ................................................. 1 Conduction, Convection, and Radiation.......................................................................... 1 Conduction ....................................................................................................................... 4 Convection........................................................................................................................ 5

Radiation .......................................................................................................................... 5 Heat Transfer in the Atmosphere .................................................................................... 5 Seasonal Variations in Temperature ............................................................................... 8 Solstices and Equinoxes ................................................................................................. 10 Greenhouse Effect ........................................................................................................... 11 Where do the Greenhouse Gases come from? ............................................................... 14 Key Points in this Chapter ............................................................................................. 16 Chapter Two: Questions .................................................................................................17 Chapter 3: Daily Fluctuations in Temperature ............................................ 1 Measuring Air Temperature ............................................................................................ 1 What Measurements Matter in Meteorology? ................................................................ 8 Daily Warming and Cooling ............................................................................................ 9 Regional Temperature Variations in the World ............................................................. 11 The Effects of Altitude on Temperature ........................................................................ 13 Key Points in this Chapter ............................................................................................. 15 Chapter Three: Questions: ............................................................................................. 16 Chapter 4: Humidity, Clouds, and Condensation......................................... 1 Evaporation, Condensation, and Saturation ................................................................... 1 Dew ................................................................................................................................... 7 Fog .................................................................................................................................... 8 Types of Fog .................................................................................................................. 9 Cloud Formation and Cloud Types ................................................................................ 10 Types of Clouds .............................................................................................................. 12 High-level Clouds ....................................................................................................... 13

Mid-level Clouds ......................................................................................................... 13 Low-level Clouds ........................................................................................................ 14 Key Points in this Chapter ............................................................................................. 15 Chapter Four: Questions ................................................................................................ 16 Chapter 5: Cloud Formation and how Precipitation Happens .................... 19 Atmospheric Stability .................................................................................................... 19 What is the dry adiabatic lapse rate? ............................................................................. 20 Moist Adiabatic Lapse Rate ........................................................................................... 22 Clouds and Convection .................................................................................................. 23 How Precipitation Forms ............................................................................................... 26 Types of Precipitation .................................................................................................... 31 Measuring Precipitation ................................................................................................ 33 Key Points from This Chapter........................................................................................ 36 Chapter Five: Questions................................................................................................. 37 Chapter 6: Air Pressure and How Wind Forms.......................................... 40 Atmospheric Pressure Changes ..................................................................................... 40 Wind Flow ...................................................................................................................... 44 How Air moves in the Atmosphere around the Globe .................................................. 49 Isobaric Maps ................................................................................................................. 53 Surface and Upper Air Charts ........................................................................................ 54 Types of Wind Instruments ........................................................................................... 57 Measuring Wind Direction and Wind Speed ................................................................ 59 Key Points from This Chapter........................................................................................ 60 Chapter Six: Questions .................................................................................................. 61

Chapter 7: Circulation in the Atmosphere ................................................. 64 General Circulation ........................................................................................................ 64 Local Wind Systems ....................................................................................................... 67 Air Pockets and Eddies .................................................................................................. 68 Lake Effects .................................................................................................................... 70 Atmospheric Ocean Interactions ....................................................................................71 Southern Oscillation .......................................................................................................71 El Niño and La Niña....................................................................................................... 74 Important Points in this Chapter................................................................................... 76 Chapter Seven: Questions .............................................................................................. 77 Chapter 8: Air Masses, Fronts, and Middle-Latitude Cyclones ...................80 Air Masses ......................................................................................................................80 Source Regions ............................................................................................................... 83 Weather Fronts .............................................................................................................. 84 Mid-latitude Cyclone Storms ......................................................................................... 85 Key Points from This Chapter........................................................................................88 Chapter Eight: Questions ............................................................................................... 89 Chapter 9: Weather forecasting ................................................................ 92 Getting Weather Information ........................................................................................ 92 Computerized Weather Forecasting .............................................................................. 95 Using Surface Charts...................................................................................................... 95 Sending out Watches and Warnings.............................................................................. 97 Reporting on Thunderstorms ........................................................................................ 97 Terms Related to Floods .............................................................................................. 100

Terms Related to Winter Weather ................................................................................101 Severe Weather Watches and Warnings ..................................................................... 102 Winter-related Advisories ............................................................................................ 103 Tornado and Thunderstorm Advisories ...................................................................... 104 Fire-Related Weather Emergencies ............................................................................. 107 Coastal or Lakeshore Hazard Warnings ...................................................................... 108 Marine Hazard Watches and Warnings ...................................................................... 109 Advisories related to Temperature ...............................................................................110 Tropical Watches and Warnings................................................................................... 111 Key Points in this Chapter ............................................................................................ 112 Chapter Nine: Questions............................................................................................... 113 Chapter 10: Thunderstorms and Tornadoes ............................................. 116 Thunderstorms.............................................................................................................. 116 Life cycle of a Thunderstorm ........................................................................................ 116 Classification of Thunderstorms................................................................................... 117 Mesoscale convective systems ...................................................................................... 119 How do Thunderstorms Move? .................................................................................... 119 Flooding ........................................................................................................................ 119 Underlying Causes of Floods ........................................................................................ 121 Flood Effects ................................................................................................................. 121 Flood forecasting.......................................................................................................... 122 Tornadoes..................................................................................................................... 122 Tornado Characteristics ............................................................................................... 124 Life cycle of a Tornado ................................................................................................. 125

Key Points in this Chapter ............................................................................................127 Chapter Ten: Questions ............................................................................................... 128 Chapter 11: Hurricanes and Other Tropical Weather Phenomena ........... 130 Tropical Cyclones ......................................................................................................... 130 Proper Tools for a Tropical Cyclone ............................................................................. 131 Stages of a Cyclone's Life Span .................................................................................... 132 Tropical Storm Terminology........................................................................................ 132 Hurricane Life Cycle .................................................................................................... 133 Tropical Disturbance (Tropical Wave) ........................................................................ 133 Tropical Storm ............................................................................................................. 134 Hurricane and its Classification .................................................................................. 134 Tracking Hurricanes .................................................................................................... 135 Naming Hurricanes...................................................................................................... 136 Famous Hurricanes.......................................................................................................137 Important Points in This Chapter................................................................................ 138 Chapter Eleven: Questions .......................................................................................... 139 Chapter 12: Our Global Climate ............................................................... 142 Global Climate and Weather........................................................................................ 142 Milankovitch Cycles ..................................................................................................... 145 Biogeography ............................................................................................................... 148 Climate Extremes ......................................................................................................... 148 Dry Spells and Droughts .......................................................................................... 148 Wet Seasons .............................................................................................................. 150 Temperature Extremes .............................................................................................. 151

Past Climate Trends ................................................................................................. 152 Natural Climate Change ........................................................................................... 152 Human-influenced Climate Changes ....................................................................... 154 Global Warming and Future Expectations .................................................................. 156 Key Points in this Chapter ........................................................................................... 158 Chapter Twelve: Questions .......................................................................................... 159 Chapter 13: Air Pollution......................................................................... 162 Types and Causes of Air Pollution ............................................................................... 162 Particulate matter ..................................................................................................... 162 Nitrogen dioxide ....................................................................................................... 163 Ozone ........................................................................................................................ 163 Sulfur dioxide ........................................................................................................... 163 Sources of Air Pollution in the Atmosphere ................................................................ 164 Ozone and its Effects.................................................................................................... 165 Role of Wind and Inversions on Air Pollution ............................................................ 167 Urban Air Pollution Issues........................................................................................... 170 Acid Rain .................................................................................................................. 170 Key Points In This Chapter ...........................................................................................173 Chapter Thirteen: Questions ....................................................................................... 174 Chapter 14: Atmospheric Optics and How They affect the Sky .................. 177 Sky Color and its Meaning ............................................................................................ 177 Moon Phenomena and their Meaning ......................................................................... 179 What is Green Flash? .................................................................................................... 181 Halos, Sundogs, and Sun Pillars .................................................................................. 182

Rainbows ...................................................................................................................... 184 Cloud Iridescence ......................................................................................................... 185 Key Points in This Chapter .......................................................................................... 186 Chapter Fourteen: Questions....................................................................................... 187 Summary ................................................................................................ 189 Course Questions and Answers ............................................................... 193 Answers to Questions.............................................................................. 236 Chapter One ................................................................................................................. 236 Chapter Two ................................................................................................................. 237 Chapter Three .............................................................................................................. 238 Chapter Four ................................................................................................................ 239 Chapter Five .................................................................................................................240 Chapter Six ................................................................................................................... 241 Chapter Seven .............................................................................................................. 242 Chapter Eight ............................................................................................................... 243 Chapter Nine ................................................................................................................ 244 Chapter Ten .................................................................................................................. 245 Chapter Eleven ............................................................................................................. 246 Chapter Twelve ............................................................................................................ 247 Chapter Thirteen .......................................................................................................... 248 Chapter Fourteen ......................................................................................................... 249 Course Answers ............................................................................................................ 251

PREFACE Most people know what weather and seasons are all about; we know what to do in a blizzard warning or hurricane watch. But do we know how these warnings are decided on or even why we experience these fascinating and terrifying weather phenomena? This course will teach you enough about meteorology to know these things and much more.

You may even be able to set up your own weather station or predict your regional weather for next week.

The course will cover everything from sundogs to global warming and air pollution. You will learn the science behind weather phenomena and should be able to apply this knowledge to fully understand why we have weather and how meteorologists make their predictions. You'll see that weather is very complex, with many factors going into whether you see a cloudy, windy, or sunny day. Let's dive into the science of weather or meteorology. Who knows? This might be your next career.

The first chapter of the course talks about the earth's atmosphere, starting with what it once looked like and how it has evolved over time. We talk about what's in the atmosphere and the air we breathe in today's time, as well as the different layers of the atmosphere from the earth's surface to outer space. We will also discuss air pressure and air density as important baseline information you need to proceed in understanding meteorology. At the end of the chapter, you should understand the physical space where our weather originates.

Chapter two looks at how the earth and our atmosphere are warmed and cooled.

Obviously, the sun plays a big role in how this planet stays warm, but there is more to it than that. We will talk about how heat gets transferred in the atmosphere, why we have seasonal and other variations in temperature, what the solstices and equinoxes are all about, and what do we mean by "the greenhouse effect". There is a great deal of talk about this effect on our planet, but, as you will learn, it is not a new phenomenon and is not an altogether bad thing for a planet to have in moderation.

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Chapter three looks more carefully at daily and regional temperature changes.

Temperature drives the weather and is the thing most people talk about every day when discussing the weather. There are regional differences and altitude-related differences in temperature; these are related to much more than how much sun you get on a daily basis.

Chapter four in the course is essentially the study of hydrology or water in the environment. Besides the temperature, you usually want to know what if any precipitation there is outside. This chapter introduces you to the processes leading to precipitation. You will learn what the different phase changes of water are called and what they look like in terms of the weather. After you read this chapter, you should gain a clearer understanding of why we have dew on the ground, foggy weather, and clouds in the sky.

In chapter 5, we will introduce you to the subject of atmospheric instability and how this contributes to cloud formation and precipitation. In truth, the atmosphere is never completely stable but there are times where there are long stretches of weather without rain or even clouds. We will also talk about how clouds form precipitation and how they form the type of precipitation you see that falls on the ground. There are many types of precipitation that range from rain to snow to everything in between.

Chapter six in the course covers the fascinating topic of wind and its effect on the weather. You will study ways to measure wind speed and direction as well as why we have wind in the first place. You will learn what isobars are and how these are used by meteorologists to determine the weather. Surface maps are interesting to look at; they also provide you with a practical way of forecasting what the winds will be in any given area as well as when to expect a warm or cold front, simply by using a surface map.

In chapter seven, we dive deeper into the complex circulatory patterns seen in the atmosphere. There are several global patterns discussed in chapter six but also many others that affect local and regional weather conditions all over the world. The oceans and large lakes exert their own effect on the earth's weather systems in numerous ways, which will be covered in chapter seven. By the time you finish the chapter, you should be able to demonstrate how and why the atmosphere behaves as it does.

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Chapter eight in the course will bring you further toward being able to predict the weather. We will have already talked about things like air cell and convection cycles but not about large air masses that affect our weather patterns. You will learn about weather fronts from the perspective of the way air masses collide with one another. In some cases, these air masses lead to mid-latitude cyclones, which are different from hurricanes and tornadoes. You will study these cyclones and how they form.

Chapter 9 finally gets around the topic of weather forecasting. We will discuss the different tools necessary to gather weather information and make a forecast. Nowadays very large computers are used to predict the global weather. We'll talk about using surface maps make predictions and the terms you will need to know in order to understand weather watches and warnings.

In chapter 10, we talk about the different common types of weather phenomena you might see, such as thunderstorms, floods, and tornadoes. Each of these has the potential to cause loss of life and severe property damage for different reasons. Thunderstorms and tornadoes tend to come together in the same weather system, while flooding can happen for different reasons, including dams bursting and heavy snowmelt in a given area.

Chapter eleven in the course delves into the topic of tropical weather phenomena, such as cyclones, tropical storms, and hurricanes. These can be powerful and damaging because of the heat that drives them coming up from the equator and other warm areas of the world. We will talk about forecasting, naming, and tracking hurricanes as well as some of the more severe named hurricanes in North America. Tropical cyclones and how they evolve are discussed at the end of this chapter.

In chapter twelve, we will talk about the global climate, including what it looks like now, what it might look like during climate extremes, what natural climate change looks like, and the effects on climate brought on by human activities. Climate and weather are not the same thing, but you will see how they are interconnected. There is a lot out there on global warming and predictions for our future; in this chapter we talk about what these predictions mean for the everyday weather in the coming years.

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Chapter thirteen in the course looks at air pollution as it applies to meteorology. There are many reasons for air pollution, not all of which are related to human activity. Air pollution has major consequences for human health; it is made worse by certain weather phenomena, like thermal inversions. We will talk about ozone and the ozone layer.

Ozone is a gas that also affects human health and our planet's weather and climate. As you'll see, urban areas are more affected by pollution than rural areas.

Chapter fourteen will help you answer some of the more fun questions you might get asked as a student of meteorology. These involve the optical illusions and interesting aspects of the sky you see as the atmosphere interacts with sunlight and moonlight.

There are many things to cover here, including why the sky is blue, why we have rainbows, and what the different types of moons and moon colors really mean. There are many other sun-related phenomena you may not understand yet that are covered in this chapter.

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CHAPTER 1: UNDERSTANDING THE EARTH'S ATMOSPHERE Without an atmosphere, we would not have any weather. This is the reason the first chapter of the course talks about the earth's atmosphere, starting with what it once looked like and how it has evolved over time. We will also talk about what's in the atmosphere and the air we breathe now as well as the different layers of the atmosphere from the earth's surface to outer space. We will also discuss air pressure and air density as important baseline information you need to proceed in understanding meteorology.

At the end of the chapter, you should understand the physical space where our weather originates.

EARLY ATMOSPHERE ON EARTH The earth itself is about 4.6 billion years old. It was formed from a consolidation of dust and gases and had little atmosphere at the time of its birth. It was hot—too hot for life— but cooled over time. Much of the early atmosphere came from volcanoes, which spewed gases like methane, hydrogen sulfide, and huge amounts of carbon dioxide—200 times more than it does now. The earth needed to cool further after that so that water would be liquid enough to settle onto its physical surface.

We call the time period from 4 to 2.5 billion years ago the Archean Eon. There was a prominence of methane in the atmosphere and no oxygen whatsoever, except that which existed in water and some complex chemicals. The oceans were young but were able to sustain primitive, which survived on sulfur-based molecules and made even more complex molecules.

At around 2.5 billion years ago, cyanobacteria predominated the oceans. These were once called blue-green algae but are not algae at all. They were the first to use sunlight for energy and photosynthetic processes to make oxygen as a waste product, using

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carbon dioxide or CO2 as fuel to make larger organic molecules. It was photosynthetic organisms like these that changed the atmosphere to increase oxygen levels in it. Even so, the amount of oxygen was 1 percent of the level we have today.

Interestingly, the sun was not as bright as it is now; still, it was warm and never froze over. This is because of the carbon dioxide and methane in the atmosphere. These are called greenhouse gases because they trap heat and keep the earth warm. It was good for the earth back then, but as you will see, it is not good for the planet today.

From around 2.6 billion years ago to about 400 million years ago, these cyanobacteria and regular bacteria made oxygen to increase the O2 gas molecules in the atmosphere and react with methane. Methane became a substrate for larger molecules and cleared away from the air. This process essentially cleared up the skies and made them blue.

More oxygen meant more oxidizing chemical reactions on earth. Iron was oxidized on the earth's surface to allow for iron oxide to form. The soil became reddened with this and related substances, which is why we still see vast expanses of it on our planet's surface.

Finally, the amount of oxygen around the earth increased dramatically. This happened in the late Proterozoic era—about 700 to 550 million years ago. Oxygen was everywhere then—in the oceans and the air. Around 600 million years ago, there was up to one-fifth the amount of oxygen we now have. Oxygen was great for some organisms but toxic to others. These latter organisms either became extinct or were forced to reside in the airless parts of the planet (where many still live).

The Cambrian explosion, which happened around 509 to 530 million years ago, was a time of huge expansion of life on earth. Oxygen probably helped fuel this expansion of living things; you would have seen billions of organisms like trilobites and eurypterids.

Oxygen was thoroughly dissolved in the ocean by 430 million years ago, giving rise to numerous species of life in these waters. Life expanded further to the land; there were plant species and a few invertebrates that crawled from the seawaters to the swampy earth. These invertebrates were able to extract oxygen directly from the air to survive.

The Devonian period from 397 to 416 million years ago marked the further evolution of plants plus the emergence of animals with four feet that roamed the planet.

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Remember that plants mean two things: the first is great numbers of oxygen molecules flood the earth; the second is that carbon waste products are available for what later will become petroleum fuel. Oxygen levels increased to nearly what we have today. This time of many plants was the Carboniferous period on earth. Oxygen levels in our early atmosphere rose from 20 to 35 percent during this period.

During this period of huge forests in many parts of the world—about 299 to 318 million years ago—there was so much carbon deposited that it could not decompose and turned into CO2 by microbes. As it got buried into airless areas under swamps, the CO2 levels dropped in the atmosphere. Without this greenhouse gas, our earth cooled. Pressure and heat took this plant decay to make coal and other products we use as unsustainable fuel sources today.

We got our modern atmosphere about 290 million years ago. Earth was once warmer than today, and there were no or very small polar ice caps. There was enough warmth for many more plants and animals in most parts of the world than we now have. It is estimated that 99 percent of all earth's species have become extinct since that time.

Can you imagine palm trees in Canada and redwood trees at the north pole? These were common in the Eocene epoch about 65 million years ago, when the earth was the warmest in recent millennia. Alligators and mammals thrived on Ellesmere island near the North Pole as well. In the higher latitudes, near the north pole, it was 45 degrees F or 25 degrees C warmer than it is now. If this trend had existed for the equator, you would see it up to 122 degrees Fahrenheit during that time—far too hot for many life forms. This extreme temperature situation probably did not occur, and temps near the equator were likely similar to what it is now.

WHAT IS THE ATMOSPHERE MADE OF? Surprisingly, despite all the talk of carbon dioxide in the atmosphere and the greenhouse effect, this gas is not anywhere near the most common gas in our atmosphere. Nitrogen predominates, followed by oxygen and argon. The next is water vapor, which makes up less than 0.25 percent of the total atmosphere by mass. Water vapor is a greenhouse gas; its concentration varies in different parts of the world. In cold

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environments, the percent of water vapor is very low; it can be as high as 5 percent in steamy tropical areas.

Other greenhouse gases are seen in small amounts and are really trace gases. These include methane, carbon dioxide, ozone, and nitrous oxide. There are several other inert noble gases in the air besides argon, but these are seen in extremely low quantities.

Don't forget nongaseous substances, such as pollen, dust, and even volcanic ash.

Pollutants can be from many sources and include fluorinated compounds, chlorinated compounds, mercery, sulfur compounds, and others.

If you sort out the typical gaseous concentration of dry air with no water vapor, you'll get these approximate amounts: •

Nitrogen 78 percent by volume

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Oxygen 21 percent by volume

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Argon 0.9 percent by volume

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Carbon dioxide 0.04 percent by volume

Trace amounts of these in order: neon, helium, methane, and krypton. This does not include water vapor, which is not seen in dry air, of course, but is seen in the air at 0 to 3 percent of measured air.

ATMOSPHERIC LAYERS There are five layers to the atmosphere, beginning at the earth's surface and extending out to what we call outer space. As you go upward away from our surface, the air pressure and air density decrease. You might expect the temperature to decrease with altitude, but this is a complex issue. The temperature can be stable in areas where you wouldn't expect it to be and might increase rather than decrease in some higher atmospheric layers. Meteorologists use instruments on balloons to detect the air temp, which provides important data on the demarcation points between the layers.

Briefly, the layers are these from the earth's surface upward: •

The troposphere extends from 0 to 12 kilometers up from the earth's surface

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•

The stratosphere is from 12 to 50 kilometers

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The mesosphere is from 50 to 80 kilometers

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The thermosphere is 80 to 700 kilometers

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The exosphere is 700 to 10,000 kilometers

Take a look at figure 1 to better familiarize yourself with these layers:

Figure 1.

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Let's look at the different layers of our atmosphere more closely:

TROPOSPHERE The air we breathe is in the troposphere up to 12 kilometers from the surface of the earth. No landmass or mountain extends this high. The thickness of this layer varies according to latitude and goes up higher at the equator. Its upper boundary is called the tropopause, where the air above is warmer than the air below this demarcation.

Throughout the layer itself, the air temperature decreases with height in most places.

This is because the earth warms the layer by transferring heat from the ground much more than the sun does.

Moisture, too, is trapped in this layer. This moistness explains why weather on earth comes from here and not from higher altitudes. You'll see clouds and wind exclusively in the troposphere, except for very high cumulonimbus or thunder clouds, which can extend higher into the stratosphere. While airplanes fly high, most commercial airliners still just fly in the troposphere.

STRATOSPHERE The stratosphere is the next-highest layer. It extends upward from the tropopause to about 50 kilometers from the ground. The atmospheric pressure is extremely low—just one-one thousandths of the atmospheric pressure at sea level. This is where the ozone layer resides. At its outer limit is the stratopause, which separates the layer from the mesosphere.

In the stratosphere, the temperature actually increases with altitude. This rise in temperature is almost exclusively due to its susceptibility to the sun's UV radiation.

Ozone absorbs the heat from the sun; mixing and turbulence is minimal, which is partly why there are patches of ozone in some places but not in others. You might see a temperature of minus 60 degrees Celsius at the tropopause but a rise of up to 0 degrees Celsius at the stratopause.

Meteorologically-speaking, the stratosphere is so stable, there is no real weather change in this part of the atmosphere. There are essentially no clouds or other weather

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phenomena, except at the poles, where there are clouds called nacreous clouds near the tropopause. Jets can travel in the stratosphere but no higher than this.

MESOSPHERE The mesosphere extends higher than the stratopause and up to 80 to 85 kilometers or 53 miles up. The upper layer is the mesopause. Temperatures plummet to this upper layer so that it will be about minus 85 degrees Celsius at the mesopause—the coldest place on our planet. The only clouds here are just below the mesopause. These come from ice-cold sublimated water vapor and are seen in the polar ice caps as noctilucent clouds. These can be seen rarely, just after sunset or before sunrise. Some have a sort of lightning called transient luminous events.

This layer is where meteors burn up on entering the atmosphere. Otherwise, it is a place of few manmade objects other than rocket-powered aircraft. Balloons and planes can't fly here, and spacecraft cannot orbit here either.

THERMOSPHERE The thermosphere is above the mesosphere. Its altitude range is from 80 kilometers to between 500 and 1000 kilometers. Its height varies so much because of differences in the sun's energy upon it. Here the air temperature increases with altitude to reach temperatures as high as 1500 degrees Celsius.

Is the air thin here? Absolutely. Imagine an oxygen gas molecule traveling as far as one kilometer before striking any other gaseous molecule. Even though these are hot, highenergy molecules, you would not feel such heat because so few gas molecules would touch your skin. There are no clouds or any water vapor in the thermosphere, but lovely phenomena, such as the aurora borealis and the aurora australis in this layer. Look for orbiting satellites here as well.

EXOSPHERE The exosphere is expansive, extending outward from the exobase, which is the boundary between the thermosphere and this outer atmospheric layer. It has no outer border but

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merges into the solar winds at about 10,000 kilometers or 6200 miles above our earth.

There are higher concentrations of helium and hydrogen gases here, although other gases are seen near the exobase. This layer is very low in density, with particles as far apart as hundreds of kilometers from one another. Particles easily escape into outer space. You may rarely have aurorae in this area, and satellites often orbit here as well.

OTHER LAYER TYPES The major layers are determined mainly by their distinct temperature differences. Other than these, you'll see other layers intermixed into the atmosphere. Here are some of these: •

Ozone layer—this is a layer contained within the stratosphere. The ozone is O3 or three atoms of oxygen together. We will talk more about what causes this molecule to accumulate. It doesn't take up much of the atmosphere—only about two to eight parts per million. You will see it between 15 and 35 kilometers above the earth but, as you may know, there are pockets of it that are thicker depending on where you look.

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Ionosphere—this is an area made by the ionization of molecules by solar radiation. It is why we see auroras near the poles. It is thicker in the daytime and extends from 50 to about 1000 kilometers from the earth's surface. Parts of it can be seen in the exosphere, mesosphere, and thermosphere. This ionization mostly happens in the daylight so, if you see auroras, these will largely be seen in the thermosphere. This layer is part of the magnetism around the earth—called the magnetosphere—which means it affects the propagation of electromagnetic signals around the world.

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Homosphere—this is the area around the earth where you'll see turbulence.

The lowest three layers are in this sphere. Above this is the turbopause at around 100 kilometers above the earth. Above this is the heterosphere, which has variations in composition by altitude and very little turbulence. Part of this lack of turbulence is due to a lack of ability of the gas particles to come too near one another. Heavier particles settle near the bottom of this layer.

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•

Planetary Boundary Layer—this is in the troposphere near the earth's surface. In the daytime, the gases are well-mixed but, in the night, there is less mixing and more stratification. It is a very narrow layer above the earth—as slim as 100 meters above ground or as thick as 3000 meters above ground.

LONGITUDE AND LATITUDE it is hard to understand meteorology without knowing the longitude and latitude system of the earth. This is the earth's coordinate system, which allows meteorologists and other people to be able to use global positioning units and tell time across the world.

Figure 2.

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Latitude is measured from the equator to the poles in degrees, with 0° being at the equator and 90° being at the North Pole or South Pole. As you know, higher latitudes generally mean colder air temperatures. Longitude is the coordinate that measures the distance around the globe circumference. There is a line designated at 0° longitude that travels around the earth from west to east and again from east to west. This line is called the Prime Meridian. Figure 2 shows you the longitude and latitude system of the earth.

Above the equator is the northern hemisphere and below the equator is the southern hemisphere. As you can see in the figure, there are several landmarks. You should know where the North Pole and the South Pole are, and you should know where the Tropic of Cancer and the Tropic of Capricorn are located in the northern and southern hemispheres, respectively. You will record latitude at any point on earth in degrees, minutes, and seconds, similar to how all angles are measured. This means that when you see a measurement of 30° 15 minutes and 20 seconds North, you will find this on the globe at this latitude in the northern hemisphere.

1° longitude and 1° latitude are approximately the same distance around the earth; these represent about 16 miles of linear travel. There are a few things you need to know about latitude. First, they are sometimes called parallels because they run parallel across the earth's surface and never meet one another. Second, they always run in the east to west direction. Third, the line that forms a given place in latitude will become shorter as you reach each pole.

The Prime Meridian was arbitrarily set to be 0° at Greenwich, London. The longitude is measured in degrees, minutes, and seconds. Longitude is measured up to 180°, which is on the other side of the world from the prime Meridian. These are not parallel lines but come together at the North Pole and South Pole. Some things you need to know about longitude are that these are called meridians, they always run in a north to south direction, and are furthest apart at the equator. Each Meridian is the same circumference around the earth.

As you can see, these coordinates are a wonderful way to map anything on earth. You just need to remember to add North or South to the latitude, and east or west to the longitude, knowing that 0° is at the prime Meridian. You also need to remember that

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longitude and latitude are flat coordinates on the earth's surface, while altitude is measured as a height above the Earth's surface.

MEASURING AIR PRESSURE AND DENSITY if you've ever heard the term barometric pressure, you should know that this means air pressure. It is the unit of measure you read when you read a barometer. There are several ways to measure air pressure, including the standard atmosphere, the Pascal or kilopascal, the millibar, pounds per square inch, and millimeters of mercury. These are all different values with the standard atmosphere set at 1 atm at sea level.

Among these measurements, the atmosphere, kilopascals, and millimeters of mercury are the most often used. When you say, "millimeters of mercury", this can also be referred to as Torr. One atmosphere is equivalent to 760 millimeters of mercury.

Atmospheric pressure equals the weight of a column of air above the point being measured. It makes sense then that when you increase altitude, this column of air will be less. This would mean that atmospheric pressure decreases with altitude, which is true. If you use standard international units of pascals, you measure the column air in newtons per square meter. At sea level to the top of the atmosphere, a square centimeter of air would weigh approximately 1.03 kilograms. So, it means air pressure is the force of a column of air onto the earth's surface. Figure 3 demonstrates the variation in air pressure by altitude.

Air pressure or atmospheric pressure is dependent on gravity. Gravity is dependent on the mass of the earth and the radius of the planet. It also depends on which gases are in the column of air and the rotation of the earth on its axis. Finally, local conditions like air density, wind velocity, temperature, and variations in the gas composition of the atmosphere in a specific location determine the air pressure you find. The term "surface pressure" means the air pressure at a particular location on earth.

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Figure 3.

There are tables you can use to calculate the air pressure once you know the altitude, temperature, and the level of humidity. There is a relatively linear decline in air pressure with ascending altitude. A good approximation is 1.2 kPa every 100 meters elevation.

There are certainly wide variations in atmospheric pressure by location, which is basically what gives rise to the lot of weather phenomena and wind, as air flows from a high pressure region to a low-pressure region.

Atmospheric pressure also varies by the time of day and shows a diurnal or semi-diurnal cycle. The reason for this is the global atmospheric tides; this is strongest in the tropical areas and almost nonexistent in the polar areas.

MEASURING BAROMETRIC PRESSURE in the mid-18th century, explorers used to measure altitude by boiling water. Water boils at 100 degrees Celsius at sea level, but boils at lower levels in higher elevations. Boiling water and measuring the temperature at which it boiled was an approximation of the elevation explorer was at.

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Nowadays, we barometers to measure atmospheric pressure. There are two types of barometers you should know about. One is called the mercury barometer; it consists of a glass column that is marked off with a closed top. There is a small cup of mercury in tube called a cistern. The mercury will rise and fall depending on the atmospheric pressure. You will see the level of mercury from the cistern measured in the mercury column. Figure 4 shows this type of barometer:

Figure 4.

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An aneroid barometer contains no fluid. Instead there is a flexible metal box known as an aneroid capsule; it is commonly made from copper and beryllium alloy. The counselor seals so that any pressure change outside the box will expand or contract the springs and lovers in the box. This expansion and contraction can be measured on a barometric reading. Figure 5 shows an aneroid barometer:

Figure 5.

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AIR DENSITY The units for air density on earth is the Greek letter rho. Like all things air density is a matter of mass divided by the volume it occupies. For example, you can measure density in kilograms per cubic meter. The air density on earth depends on three things: air pressure, temperature, and the percent of water vapor in the air.

Temperature affects density by increasing the kinetic energy of gas molecules so that they bump against each other more readily if you heat up a balloon, the balloon will expand and the density inside it will decrease. This is because heat decreases air density.

Pressure on the other hand will increase air density; when you press down on a bicycle pump handle air becomes compressed and its density increases. Altitude affects air pressure; as you know, air pressure decreases with altitude. This means that higher altitudes involved less dense air. Whether systems do affect air density but not as much as altitude.

When you climb a tall mountain, you will experience some degree of air hunger. This is not because the concentration of oxygen is less than at sea level. Instead, it is because the air is less dense and you perceive less oxygen when you breathe it in. You will not notice this on an airliner because the air inside the airplane has been pressurized.

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KEY POINTS IN THIS CHAPTER •

The Earth's early atmosphere was largely formed by volcanic activity.

•

The 3 most common elements in our atmosphere our nitrogen, oxygen, and argon.

•

There are 5 major atmospheric layers, which are mostly different by their temperature.

•

You should know the different layers and understand that our weather largely comes from the troposphere.

•

Air pressure varies mostly by altitude and is measured with a barometer.

•

Longitude and latitude are coordinate systems around the earth imported in weather determination.

•

Air density is a matter of air pressure, temperature, and humidity.

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CHAPTER ONE: QUESTIONS 1.

About how old is the earth? a. 6.2 billion years b. 2.5 billion years c. 8.3 billion years d. 4.6 billion years

2.

If you measured the early earth's atmosphere, which gas would be seen in the least amount? a. Methane b. Oxygen c. Carbon dioxide d. Sulfur dioxide

3.

In our atmosphere, there are many gases called greenhouse gases. Which of these is not one of them? a. Nitrous oxide b. Nitrogen c. Water vapor d. Ozone

4.

Which gas in our atmosphere greatly changes depending on the part of the world the gases are measured? a. Nitrogen b. Oxygen c. Argon d. Water vapor

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5.

Which layer around the earth is closest to our earth's surface? a. Exosphere b. Thermosphere c. Stratosphere d. Troposphere

6.

What layer around the earth accounts for most of the weather patterns and clouds we experience on this planet? a. Exosphere b. Stratosphere c. Troposphere d. Mesosphere

7.

What feature will you least likely see in the thermosphere layer of the atmosphere? a. Noctilucent clouds b. Aurora australis c. Aurora borealis d. Orbiting spacecraft

8.

What least defines the heterosphere layer around the earth? a. Stratification of gas concentration b. Lack of turbulence c. High temperatures d. Low gas density

9.

Which Statement is not true of higher latitudes? a. The lines began to intersect b. There is more seasonal variation in weather c. there are more temperature extremes d. the circumference of each parallel decreases

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10.

If you are measuring air pressure and get a measurement of 1 atm, how many torrs would this represent? a. 16 b. 145 c. 4000 d. 760

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CHAPTER 2: COOLING AND WARMING THE EARTH Everyone knows it is generally warm during the daylight hours and cooler at night.

Obviously, it's the sun that contributes the most to this phenomenon. This also happens on other planets and on the moon but, without an atmosphere, the days are extremely hot, and the nights are bitterly cold. Why doesn't this happen on earth, too? Also, why do we have seasons, and why is it warm in the tropics but so cold at the poles? These and other intriguing questions are part of this chapter.

CONDUCTION, CONVECTION, AND RADIATION Before we talk about the atmosphere directly, we should look at how heat gets transferred. Some of this you know already. The sun's rays warm the earth, and you feel warm sitting in it. You touch a hot pot on the stove, and you get burned. These are different processes that transfer heat.

You should understand first that heat is energy. It is treated in physics as not much different from the energy you put into pushing your car out of a ditch or the potential energy of an object on top of an incline. Energy is just energy; it doesn’t matter much from where it comes. Also, there is no such thing as "cold energy". You cannot get negative cold energy flowing into a hot object to cool it. Adding an ice pack to a hot surface can only transfer energy one way: from hot to cold. It may seem that way but, in physics, this just doesn't happen.

All cooling happens by dissipating heat. Hot things in a cold environment will dissipate heat much faster than warm things in a cold environment. This means that the temperature difference between two objects will determine the rate of heat transfer.

When heat flows from one place to another, this involves a direct movement of heat or thermal energy. There are different ways to dissipate this heat, however.

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Figure 6.

What happens to a gas when it heats up? If you could look at the atoms and molecules of a gas being heated, you would see a perfect example of why heat is energy. Heat increases the kinetic energy of the gas molecules being heated. These molecules vibrate and move more rapidly, resulting in enhanced movement. Take a look at figure 6 to see

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the different types of energy involved. You should know these forms if you want to understand how one energy form becomes another in many physical systems.

Movement itself is what kinetic energy really is. Because of the random movement of heated particles, those with a high kinetic energy travel to areas where the kinetic energy is less. In other words, because of this phenomenon, heated gases will dissipate into areas where there are cooler gas molecules. Again, HEAT is ENERGY. It goes from one place to another because of the kinetic energy of gas molecules. COLD GASES have LESS kinetic energy. This is why heated gases spread and to colder areas and not the other way around.

Let's look now at the different ways heat gets transferred. There are basically three separate ways where heat gets transferred. These are convection, conduction, and radiation. Figure 7 shows you what these might look like:

Figure 7.

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CONDUCTION Conduction involves the direct transfer of heat from one object in contact with another.

This is the kind of heat you feel when you touch a hot object. On a tiny molecular level, you can say that the heat gets transferred because molecules themselves touch each other—molecules with a high kinetic energy contact with low kinetic energy molecules.

The end result is that these slower molecules move faster and are also warmer.

In order to have conduction, you need to have some type of temperature gradient between the 2 objects, a decent surface area where the 2 objects are touching one another, a short length of travel of the molecules, and properties of both substances that promote conduction. The temperature gradient is the main factor in managing the rate of heat travel and the direction it travels in. Once heat energy has been transferred, and equilibrium is reached where there is no appreciable difference in the temperature of these objects.

A larger object will have a greater mass compared to its surface. This means that it will need more energy to heat it and will also lose heat slower than a small object. Smaller objects also have a smaller cross-sectional area to contact with; this leads to decreased heat transfer from this object.

The physical property of an object will also determine whether or not it conducts heat. If you think about it, certain substances do not conduct heat very well at all. You use these substances to make things like potholders and thermal insulators. Some thermal insulators, such as you would use in a thermos, involve air between the layers of the thermos. Air is a gas that does not conduct heat very well. Things like copper used to make copper pots conduct heat extremely well.

In meteorology, few things come in direct molecular contact with one another. This means that you will see very little conduction involved in heat transfer in the atmosphere.

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CONVECTION The process of convection involves the movement of air or liquid but not solids. This is because there must be some flow of molecules within the substance. You heard the term "hot air rises", haven't you? It is because heat makes the air less dense. Any substance that is not as dense will rise. So basically, hot air rises in any room of your house. This will displace cold air so that this will be at the bottom of any room. This phenomenon also happens in the atmosphere. We'll talk more about convection in the air as it applies to weather.

RADIATION Thermal radiation is different from convection because it involves the emission of heatwaves in the form of electromagnetic radiation. Electromagnetic radiation involves waves being carried away from an object through any transparent medium or a vacuum.

The waves we experience as heat from the sun are not the light waves but the infrared waves.

You can measure the emissivity of a radiator, knowing that an ideal radiator has a value of 1. On earth, we use solar cells, also called photovoltaic cells, that collect light and change it into electricity. These are not terribly efficient, with the most efficient cells able to transmit the energy from light to electricity at just 22 percent.

HEAT TRANSFER IN THE ATMOSPHERE Heat obviously gets transferred throughout our earth's atmosphere. How this heat is balanced between the input to the earth and output into the atmosphere can be referred to as the earth's heat budget. The idea is to make sure the input and output are the same. Figure 8 shows you a bit about how this is done:

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Figure 8.

The source of incoming heat is, of course, the sun. Less than half of it gets absorbed by our planet itself, but if you add above-ground absorption, you'll get about 70 percent of the total sun's rays and heat. The rest is deflected away from earth by cloud cover, reflected off the earth's surface, or scattered by atmospheric molecules. Some—about 23 percent—goes on to be absorbed by parts of the earth above the ground. These include water, clouds, air, and dust. Heat gets conducted to different parts of the earth, while things like water, CO2, and clouds radiate energy back to space.

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Conduction happens between the earth and the atmosphere as these are in contact with one another. Air is an excellent insulator, so it keeps a lot of the earth's heat on the ground. The earth also radiates heat using infrared radiation coming from all substances on this planet. The earth is warmed and then radiates back out 16 percent of solar energy into spaces. Much, however, gets absorbed into the atmosphere before it can get to outer space.

We will talk much more about the greenhouse effect. The idea behind this is that certain shortwave radiation from the sun passes to earth through the atmosphere. It gets absorbed before getting transmitted back out to space, this time as long-wave radiation.

This long-wave radiation is harder to get out to space, and some gets trapped by CO2, water vapor, and methane. This is the main reason why the earth is warm. Without this handy feature, the earth would average negative 18 degrees Celsius. This is too cold to sustain life.

When we get all up in arms about the greenhouse effect, it isn't the effect itself we worry about but the fact that the effect is becoming more intense. Industry, animal husbandry, and pollution all contribute to the addition of methane and carbon dioxide to the atmosphere. The CO2 concentration alone has bumped up by 25 percent in the last century, and we've gained about 0.5 degrees Celsius in average temperature during this time. This is forecast to continue, leading to disastrous weather complications.

There is a lot of latent heat involved in how heat gets exchanged on earth. Latent heat is stored in a substance and released when it changes phases from liquid to solid to gas.

You cannot evaporate water without adding a ton of heat at the very end of this process.

Heat goes back into the ocean when water vapor condenses and falls as rain into the ocean. These heat exchanges happen when also with the phase change from water to ice and back.

The earth is not flat; this means that, even in those parts that receive sun at the same time, the surface does not see the same amount of radiation from the sun throughout.

Parts of earth heat more thoroughly than others. Much of this problem is due to the fact that light will strike at 90 degrees in some places but at an angle in others. Where it is 90 degrees, the solar radiation will be more concentrated and essentially stronger

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because of this. It is simply a matter of more heat per square area reaching the equator compared to the poles.

Another factor to consider is what's called albedo. This is a measure of the reflectivity of the sun's rays. A higher albedo means more reflection of these rays. Obviously, the lighter the surface, the greater is the albedo. All of the snow and ice at the poles results in a higher albedo; it means fewer of the sun's rays will be warming in this area. Clouds also increase the albedo. These are all reasons why the poles are so much colder than the equator.

The equator has a balance of heat where they receive much more heat than they give off or emit; the poles, on the other hand, give off more heat than they receive. You would think then that the tropical parts of the world just get hotter and that the poles would just get colder. This does not happen, however. Why could this be? The reason behind this is that the heat in the equator flows out and up toward the poles. About 20 percent of this heated air leaves the equator and moves toward the poles. This replaces the partial deficits you see at the poles and balances out the equator surplus and polar deficits in heat balance.

You can see where a lot of weather is the result of heat movement on the earth. When heated air moves, it must travel on the wind. Whenever wind travels, you will have weather. Heat, of course, hardly ever travels in a straight horizontal line across the earth. Because of convection, hot air will rise before traveling where it needs to go. As it cools in higher latitudes, this air drops down again. Winds blow over the oceans, affecting sea life everywhere.

SEASONAL VARIATIONS IN TEMPERATURE There are temperature differences across the entire earth and what are called diurnal variations, which are differences from day to nighttime temperatures. The sun warms the air and the earth but, during the night, we must rely on retention of that heat in the rocks, water, and atmosphere in order to keep the dark parts of the world from freezing every night.

These are the known temperature differences in meteorology you should remember: 8

•

Diurnal Variation—this is the night to day differences we just discussed. There is radiation from the sun during the day to warm the earth; at night, there is radiation from the earth's surface that has been stored there to keep the earth warm. The atmospheric temperature remains in a cooling trend until the sun warms up in the mid-morning time. This means you'll see the minimum temperature generally after sunrise and not before it. It explains why we have fog shortly after sunrise. More on that later.

•

Seasonal variation—because the earth has a tilted rotation on its axis, the sun reaches different parts of it in various ways during a year. Without this tilt, we would have no seasons. Remember that this tilt allows for more solar energy in the Northern Hemisphere. At the same time, there is less solar energy in the Southern Hemisphere. The summer and winter seasons are reversed in these two hemispheres.

•

Latitude Variations—this is the temperature variation due to the curvature of the earth. As we just discussed, the sunlight reaches the earth at an angle that varies according to the latitude on earth. As you know, the equator would most likely be much hotter than anywhere near the poles.

•

Topographic Variations—these are variations related to where you happen to be on the earth. Water absorbs heat better than solid earth. It also does not lose this heat very quickly. It means that near larger bodies of water, you will not see great temperature changes compared to areas without water. Wet soil or swampy areas will also minimize changes in temperature. Other things that retain heat are dense vegetation, while drier areas with little vegetation lose heat faster. Look for greater diurnal and seasonal variations in temperature in areas where there is less moisture and vegetation. Areas with lake effect winds from large lakes or the ocean have less variation in temperature over time.

•

Altitude Variations—the term "lapse rate" is the decrease of thermal temperature with increasing altitude. It averages about 2 degrees Celsius per 10000 feet increase in elevation. This will vary, however, with the circumstances.

In addition, an inversion can occur, where this is reversed, especially at night,

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when the ground cools faster than the air. This would mean that a higher elevation would transiently be warmer. In addition, if there are high winds aloft over cold air, you will also get an inversion situation.

SOLSTICES AND EQUINOXES In studying meteorology, you should know what the equinoxes and solstices are. These are key times of the year when the length of days and nights reach certain milestones.

Let's look at what these milestones look like: Vernal Equinox—this is also called the "spring equinox". It is the time period around March 20th of each year when the length of daylight is nearly equal to the length of nighttime. The earth's tilt is minimal during this time, and the sun is overhead during noontime. The time and day vary from year-to-year, mostly because the sun and our planet do not go by our artificial calendar. The days continue to get longer after this.

Autumnal Equinox—this is the identical issue to the vernal Equinox, except that the days are now becoming shorter. It occurs within a few days of September 20th. With both the vernal and autumnal Equinox, the rate of change of the days and nights is the fastest. This is because the sunrise and sunset are set into sine waves. As you reach the upswing or downswing of these sine curves, the rate of change will be the greatest.

Summer Solstice—this is the peak time when the earth's tilt is maximal with respect to the sun. It happens around June 20th each year. The sun is high in the sky on this day in the northern hemisphere. The exact moment happens when the sun is immediately above the Tropic of Cancer at 23.5 degrees latitude in the north. It is the longest day of the year in the Northern Hemisphere.

Winter Solstice—this is the shortest day of the year in the Northern Hemisphere and happens around December 20th. It occurs at the exact time when the sun is directly above the Tropic of Capricorn at 23.5 degrees latitude in the south. With both the summer and winter solstice, the shortest day of the year is not the same as the latest sunrise and earliest sunset. This is because the sine curves for sunrise and sunset are not in phase with one another. In the northern hemisphere, the sunset will get later before the sunrise even starts to happen earlier in the day.

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GREENHOUSE EFFECT

Figure 9.

As mentioned, the greenhouse effect is a normal part of the earth's ability to warm itself; it has been around since there was an atmosphere on this planet. There are gases in the atmosphere that reflect the sun's rays and those that either absorb them or retain the heat already on the surface of the earth. There are certain gases labeled greenhouse gases, including methane, CO2, water vapor, ozone, nitrous oxide, and others. We will 11

talk about these soon. Without the energy we retain from these gases, the earth would be about 33 degrees Celsius than would be the case without them.

Figure 9 shows the greenhouse effect, including what we see as mankind's contribution to it: There are several steps to the greenhouse effect that are worthwhile to consider. Let's outline how this works: •

Step 1: Rays from the sun reach our earth. Some rays get absorbed, while others are reflected back into outer space.

•

Step 2: Solar radiation that enters the atmosphere reaches the oceans and land.

The earth becomes warmer as a result.

•

Step 3: Heat radiates outward from the earth back into space, which is more noticeable at night when the sun is not adding heat to the earth itself.

•

Step 4: Not all of this heat can get back out. The wavelength of heat changes (lengthens), so there is a higher likelihood of having heat trapped. This is helpful to life on earth because it reduces the chance of wide temperature variations on earth.

•

Step 5: Human activities have greatly contributed to the worsening of the greenhouse effect, which has the effect of increasing our global temperatures in ways that will affect our weather patterns.

The sun provides energy in several ways. There are rays in the ultraviolet, near-infrared, and visible spectrum. These provide different things. This image (figure 10) shows the electromagnetic spectrum. The circle around the sun shows its range on the spectrum:

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Figure 10.

The visible spectrum is where we get light. The UV spectrum does not provide heat but will cause sunburn. It's the near-infrared rays that provide the heat to the atmosphere.

As mentioned, the wavelength coming into the earth will not be the same as the wavelength of light leaving the earth. This is because the earth is colder than the sun.

Shorter wavelengths (like visible and UV light) pass through the atmosphere more easily. It's as though they have a straight shot to the earth and bypass the molecules of gas in the atmosphere. Longer waves (like infrared rays) get trapped more easily by gas molecules, so it is harder for these to leave the earth. Too much of these low-wave heatwaves and you get more heat trapped on earth.

Greenhouse gases are called by this name because of their size and characteristics. Their main characteristic is that they absorb these infrared-range heatwaves so that they can trap heat more effectively. The different gases vary according to their ability to do this.

You can think of these gases as having certain wavelengths they best absorb, with a great deal of overlap. If you add the ability to absorb heat waves and the percentage of the different gases in the atmosphere, you can imagine there are different impacts of the gases on the greenhouse effect.

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Water vapor and carbon dioxide are both strong absorbers of heat, so they are stronger greenhouse gases than methane and ozone. Water is the strongest of these but, as CO2 has an overlapping effect with water vapor, it closes a window of wavelengths that would otherwise escape.

By looking at the different effects on the atmosphere, you can rank their importance as follows: Water vapor is greater than carbon dioxide, which is greater than methane, and finally, ozone. With so much talk about ozone, you might be surprised that it absorbs only 3 to 7 percent of the total heat radiating from the earth.

As mentioned, the importance of these gases is partly due to their concentration and partly due to their trapping ability. Methane is very powerful, able to trap more than 20 times more heat than CO2. It's concentration, however, is reduced, so its impact is less.

CFC-12 (an aerosol product) traps more than 10,000 times as much as CO2. This is why there is a ban on using these products in aerosol cans.

WHERE DO THE GREENHOUSE GASES COME FROM? There are actually several different greenhouse gases besides those we've just discussed.

Most people know what they are but don't know where the different gases come from.

Let's look at what these are and where they come from: •

Carbon dioxide or CO2—this comes from animal and human respiration, plant decompensation, and fossil fuel burning.

•

Methane—this comes from gas expelled in ruminant animals (usually domesticated animals) and from the decomposition of some plant material.

•

Nitrous oxide—this is made by bacteria and plays a small role as a greenhouse gas.

•

Ozone—this comes from atmospheric processes that take diatomic oxygen and turn it into a three-oxygen molecule.

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•

Chlorofluorocarbons—these are given off by things like aerosols or in industrial properties.

The enhanced greenhouse effect refers to the fact that human activities have contributed to an increased risk of global warming due to having more greenhouse gases in the atmosphere. The things we do to contribute to greenhouse gases are deforestation, burning of fossil fuels, and animal husbandry. It is also called anthropogenic global warming. We will talk a great deal more about the effect of this phenomenon on our weather on earth as we go through each chapter.

Carbon dioxide is an important gas humans contribute to the atmosphere. The level in 1960 observed at the Mauna Loa Observatory was 313 parts per million. When recently checked in 2013, this value was 400 parts per million. This exceeds the amount of CO2 found in ice core information from any time before we had industrialization came to the earth.

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KEY POINTS IN THIS CHAPTER •

There are several types of heat transfer, from conduction to radiation to convection.

•

In convection, hot gases become less dense and then rise to the surface, pushing down cold air to the bottom.

•

Air temperature averages vary with season, time of day, latitude, and altitude.

•

The solstices and equinoxes mark certain times in our seasons.

•

The air is warmed by the radiant heat coming from the sun, is absorbed by the earth in varying degrees, and is then rewarmed by the earth giving off its warmth at night.

•

Without greenhouse gases, the earth would not stay warm at night.

•

Enhanced greenhouse effect comes from human activities adding greenhouse gases to the atmosphere.

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CHAPTER TWO: QUESTIONS 1.

Energy applied to a gas causes a transfer of what energy form to which energy form in the system? a. Potential to kinetic b. Thermal to kinetic c. Kinetic to ionization d. Chemical to electromagnetic

2.

What factor is most significant in determining the rate of heat transfer in conduction? a. Properties of the substances involved b. Distance the molecules must travel c. Surface area where heat is conducted d. Temperature gradient between objects

3.

About what percent of the sun's heat energy is actually absorbed by the atmosphere or ground? a. 100 percent b. 70 percent c. 50 percent d. 25 percent

4.

Which statement is not true of the greenhouse effect? a. Methane and CO2 are common gases responsible for this b. It allows for life on earth to exist c. It allows for warmth retention on earth in the nighttime d. It is due to manmade factors

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5.

Which area on earth would most likely cool faster at night? a. Dry desert tundra b. Mid-Atlantic Island c. Near Lake Superior d. Swampy area

6.

Assuming you are on an average mountain and decide to ascend 2000 feet.

What is the expected decline in air temperature as you make the ascension? a. 2 degrees Fahrenheit b. 2 degrees Celsius c. 4 degrees Celsius d. 8 degrees Celsius

7.

What aspect of our planet prevents heat loss during nighttime hours? a. Tilt of earth's axis b. Atmospheric gases c. Convection processes d. Ground cover and vegetation

8.

What wavelength coming from the sun is most responsible for heating the earth's surface? a. UVA b. Visible c. Infrared d. Microwaves

9.

Which greenhouse gas has increased dramatically because of the domestication of cattle and pigs? a. CFCs b. Methane c. Ozone d. Water vapor

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10.

Which gaseous molecule in the atmosphere has the greatest ability to trap thermal heat from the earth radiating into outer space? a. CFC b. Methane c. Ozone d. Water vapor

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CHAPTER 3: DAILY FLUCTUATIONS IN TEMPERATURE Now that you know something about warming and cooling the earth, we will talk more about how temperature fluctuates over time and space. You should first understand how best to measure temperature in your area and what temperature charts look like. There are diurnal fluctuations you need to know about as well as variations in temperature by region and altitude.

MEASURING AIR TEMPERATURE Suppose you want to know what to wear today and you don't have a TV or radio person to tell you what to do. You might go outside or open a window just to see if it is raining and how warm it feels outside. You might look at the cloud pattern because clouds mean the temperature won't get as warm during the day. If you have a thermometer, you may check it.

What are you really checking when you feel the air temperature? Remember that air is just a collection of gases and that the temperature of these gases determines the kinetic energy or movement of these molecules. You literally feel the movement of these molecules, which is how you perceive temperature. Because of the fact that you feel these molecules as part of temperature, density also matters. If the density is low, the temperature you feel will also be lower than expected.

When you measure air temperature, you generally use a thermometer. There are many types of thermometers you can use. We will talk about how these work in a minute.

When you check the temperature, you use one of two common scales. The scale used throughout much of the US is Celsius, in which water freezes at 0 degrees Celsius and boils at 100 degrees Celsius. Fahrenheit is a nonstandard measure of temperature first

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proposed in the late 1700s. With this scale, water freezes at 32 degrees Fahrenheit and boils at 212 degrees Fahrenheit.

What you'll notice is that these scales are not completely different. One degree Fahrenheit is only 0.56 degrees Celsius. For every degree Celsius change, you'd get a change in Fahrenheit of 1.8 degrees. If you need to do a quick calculation from Fahrenheit to Celsius try this rough formula: 1. Take the temperature in Fahrenheit 2. Subtract 30 from this number 3. Divide the number you get by 2.

For the Celsius to Fahrenheit conversion, take your number and multiply by 1.8 before then adding 32 to get your answer. You should know that in Standard International units, temperature is measured in Kelvin units. This is the same scale in terms of degrees as the Celsius scale but starts at zero being absolute zero, where no atomic motion can occur. This is -273 degrees Celsius and is a number that cannot realistically be achieved. This means that water freezes at 273 degrees Kelvin and boils at 373 degrees Kelvin.

The temperature in almost every part of the world will be posted in degrees Celsius. The only countries who report the temperature in degrees Fahrenheit are Liberia, Myanmar, and the United States.

Always measure your air temperature in the shade. You will have a vastly different and incorrect temperature reading if you try to put the thermometer in the sun.

Temperature is one of the most important factors in meteorology. It drives currents of air and affects what type of precipitation you will have. Air dryness or humidity levels are also very temperature-dependent. Temperature is unique among the different meteorological variables because it is not dependent on the mass or volume of a substance. It is instead related to the amount of energy in the substance. Heat is a type of energy but, while you measure temperature with a thermometer, it is not exactly heat you are measuring. Temperature is just a way to have a graded way of determining hot versus cold.

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Temperature is important in meteorology mostly because it is the strongest determinant of the amount of water vapor in the atmosphere. In terms of humidity, the most humidity one can have is 100 percent relative humidity, except in rare cases.

Temperature also determines what phase water or precipitation will be in. We will learn a lot later about things like sleet, drizzle, rain, and all other forms of precipitation that are temperature dependent.

Before we discuss temperature, we should talk about a term called air parcel. In meteorology, an air parcel is a collection of air with an ill-defined number of particles in it but that has enough particles so that you can say the entire parcel is uniform. Air parcels cannot be defined in terms of any size or quality; is only a parcel of air that is stable with respect to its characteristics.

So, back to temperature. You cannot understand atmospheric processes without knowing what the different temperatures are in the various air parcels in a certain area.

As always, hot air rises and cold air falls, but you also have to think about what happens when a warm air parcel meets a colder air parcel in the environment. Finally, as air cools you will see the condensation of the water vapor in it because the temperature can no longer hold the gaseous water molecules, so these precipitate out in the form of clouds and rain.

There are actually many types of thermometers you can use measure temperature. Let's look at a few of these: •

Liquid in glass thermometers – these have been around for 2 centuries or more and are very inexpensive. These are the typical Mercury or alcohol thermometers that expand with heat. They are placed inside a glass tube that has gradations on it so you can measure the temperature of the liquid inside the glass tube. It is based on the idea that everything expands when heat is added. One of the major downsides is that it requires a living person to go out there and read them. This makes these poor choices for weather sensing on a large scale, even though they are accurate and stable temperature sensors.

•

Maximum-minimum liquid in glass thermometers – these are use simply to record the high and low temperature over a period of time. It is a U-shaped

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thermometer with mercury and liquid in it. The maximum and minimum temperatures are marked with markers that need to be reset after reading the temperature.

•

Platinum resistance thermometers or PRTs – these are based on the idea that metals have certain electrical resistances based on ambient temperature. Fine platinum wires are imbedded into a nonconducting substance and the temperature is recorded as a function of the resistance of the metal wire. These work well but the platinum wires are very fragile. Once calibrated, these are very accurate and can be fully automated.

•

Bimetallic thermometers – these are used in cooking and are often the ones you see outside a home mounted on the wall. They contain no liquid but instead have 2 welded strips of metal coiled into a spiral inside the thermometer. Because different metals expand and contract with heat in unique ways, the uneven expansion of the metal strip can be measured and marked on a thermometer.

•

Thermistor – thermistor is an electrical thermometer that uses the relationship between electrical resistance and temperature. This is the kind of thermometer you probably have on your car dashboard. It is also the type of thermometer used in weather balloons that need to measure temperature by the atmosphere. The main difficulty with these sensors is that they need to be calibrated, which is hard to do. Once calibrated, they do not need frequent calibration and can be accurate outside of normal atmospheric ranges.

•

Thermocouple sensors – these depend on two different metals that react differently to temperature. They will be two different wires attached to a reference junction and a measurement junction. The voltage differences across these junctions will help determine the temperature. The voltage difference in one thermocouple setup will be so small that the thermometer will have the potential for interference unless many thermocouples are used together to allow for higher voltages. These will resist interference better.

•

Sonic sensors – these unique sensors are based on the speed of sound in air at different temperatures. These are expensive and depend on the humidity level 4

and winds. Because of these factors, the sensors must send sound in different directions to account for the wind. The humidify must also be known and used to determine the real temperature. The advantage is that they are not sensitive to the sun's radiation.

•

Radiometric sensors – these are heat sensors that are used by chefs to determine food surface temperature. In meteorology, they can be used to make cool maps of surface temperatures of large expanses of water and land. They are not very accurate as they only measure the top skin of a surface and say little about the real temperature beneath the surface. They can be mounted on aircraft to tell cloud, ocean, and land temperature variations.

When placing a weather thermometer, you should put it approximately 5 to 6 feet above ground level, but not over a paved or dark surface. Again, it should be placed in the shade and never exposed to direct sunlight. Among the different thermometers, the thermistor is most accurate in direct sunlight. Do not place a thermometer too close to a building, as buildings radiate heat.

Figure 11.

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The US Weather Service relies on special thermometers placed at more than ten thousand US sites. These are placed in shelters called cotton-region shelters or Stevenson Screens. Each is about five feet from the ground and is open on the sides in order to have free air flow across the thermometer region. They are all painted white in order to prevent heat absorption from the sun's rays. They are protected from precipitation as well. Figure 11 shows what these shelters look like: Airports have their own system, called the ASOS or Automated Surface Observing System, that are also sheltered. Home weather stations usually are shielded as well. Any thermometer reading you see on a bank building, in your automobile, or exposed to direct sun should not be trusted as being accurate. Thermistors in cars are not in direct sun but are located too near the grille of the car to be accurate. Your most accurate automobile reading is when you are moving quickly down the freeway without stopping.

Field thermometers at sporting events are too high off the ground and are often exposed to direct sun.

A graph of temperature and altitude from the surface of the earth to the exosphere would be interesting. These are the trends you would notice from the earth's surface to outer space: •

Troposphere – there is a gradual decline in temperature with altitude that is roughly linear.

•

Stratosphere – all of the lost heat at the line between the troposphere and stratosphere is regained as one travels up to the mesosphere in a roughly linear way.

•

Mesosphere – all of the temperature at the line between the stratosphere and the mesosphere is lost by the time you get to the thermosphere. This line at the top of the mesosphere (the mesopause) is where the lowest temperatures on earth are recorded.

•

Thermosphere – there is a marked increase in temperature above the mesopause to very high levels; the rate of increase is the fastest just above the mesopause but slows within 10 kilometers above this line.

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•

Exosphere – the temperature remains high but there are so few molecules of atmosphere here that it would not be at all noticeable. There is very little temperature change from the bottom to the top of the exosphere.

Figure 12 shows you what the different temperature schemes might look like:

Figure 12.

There are some interesting temperature facts about Earth you might want to learn, including these: •

Lowest recorded temperature on earth was -128.6 degrees F or -89.2 degrees C

•

Average temperature on earth is 61 degrees F or 16 degrees C.

•

Highest temperature ever recorded on earth was 129.2 degrees F or 54 degrees C.

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WHAT MEASUREMENTS MATTER IN METEOROLOGY? If you want to know what to wear on any given day, you need to check the air temperature as we just discussed – in the shade about 5 feet off the ground. In meteorology, however, different measurements are taken to determine the weather.

Things that are also measured include ground temperature or land temperature. The land temperature is often higher than the air temperature. There are temperature sensors that have inlets just above the ground and at 2 meters above the ground.

Other measurements include satellite-based temperature sensing and measuring the soil temperature at various depths. Soil depth temperatures tell farmers when they should plant their crops successfully. These measurements need to be taken locally because they are below the ground.

Water temperatures are done using ships, remote buoys, and other devices. They can simultaneously measure the air temperature. Remote water sensing is important over large bodies of water; these are important because water temperature is very important in determining the climate and weather. Tropical storms are partly dependent on the water temperature, so these values are important. You can also measure the sea surface temperature using satellites. These satellites have shown an increase in global water surface temperatures in the last century. These temperature are gotten using radiometric testing.

Meteorologists also use what's called the global sounding network, which looks at temperatures throughout the atmosphere. The most common thermometers used are small bead thermistors or perhaps platinum resistance thermometers attached to balloons that measure the temps of the entire troposphere and the lower aspect of the stratosphere. The devices that do this are called radiosondes. They measure other atmospheric parameters, such as humidity and air pressure. A GPS device says where the device is located around the earth. Radiosondes are launched by balloons twice daily at 800 sites around the globe.

There are also devices called dropsondes that are connected to parachutes dropped from aircraft to check the temperature as the parachute drops from the plane. They are often

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dropped in areas of interest or in parts of the world that are inaccessible due to being in the ocean or a sparsely populated land area.

If you think about it, aircraft offer good opportunities to measure temperature in the upper regions of the atmosphere. They often use thermistors or platinum resistance sensors on the housing of the plane, where they can be protected from the elements and where they can accurately measure air temperature.

Aircraft probes come in two different types: one is a fast response probe and the other is a heated probe. These need to be protected from the airstream exerted by the plane, mostly because the platinum resistance wires are so fragile. There is also supercooled liquid up in the clouds that will affect these probes. Heated probes can protect themselves from this buildup of supercooled liquid. Heated probes will still measure temperature but they need to make a calculation to adjust for the heated housing around the probe.

There are special devices used to measure the global temperature as well. Measuring the temperature of the globe is very important in understanding global warming. Because not all parts of the globe have the ability to measure surface temperature, there are networks in place that can account for this. Numerous ocean devices like buoys are used to get a giant grid that will tell meteorologists what the average surface area is in all parts of the globe.

DAILY WARMING AND COOLING It is no surprise that it is warmer the daytime and cooler at night. This is called a diurnal temperature variation. In general the diurnal maximum occurs somewhat after noon on any given day. This is because the air will keep absorbing the sun's heat after it is past its maximum. Also, the diurnal low temperature or minimum occurs a bit after dawn; it is because the sun has not begun yet to warm the earth.

You need to understand that the sun eats only a small layer of the atmosphere just above the surface of the earth. It may only be one to 3 centimeters. This heat rises so that eventually the air around us is warm. If you measure the temperature on the ground and the temperature around one meter above the ground, you may see up to a 30 degree 9

Fahrenheit difference. As you can see, the convection process that heats the whole atmosphere is somewhat inefficient.

Certain areas on the earth have a much greater diurnal temperature variation than others. High desert regions, for example, have low humidity and little vegetation, resulting in a large diurnal variation in temperature. Humid areas have a lesser degree of variation in temperature from daytime to nighttime. The largest extreme in temperature documented has been about 102 degrees Fahrenheit; one of these was documented in Montana in 1972. This happened because of Chinook winds coming from Pacific Ocean into the mountainous region of the West.

Interestingly, agriculturists care a great deal about diurnal temperature variation.

People who grow grapes for wine know that large swings in temperature day to night will make their grapes have a high acid content and high sugar content. This is preferable to most winemakers.

While you would think that the sun warms the earth through radiation, this is only partially true. The sun's rays hit the ground and warm it. Through conduction, the earth then warms a small layer above it. This thin layer heats the cool column of air just above it and eventually this warmth reaches higher in the air. You can imagine then that it is on the ground in the daytime where you would get a higher temperature than anywhere else. Again, because this is a slow process, your highest daily temperatures will be in the afternoon and not at noon itself. In general, you can expect a peak temperature between 3 and 5 PM in your neighborhood.

There are certain things that affect the diurnal temperature variation in your area. Let's look at these: •

Day length – shorter days mean a reduced diurnal variation, simply because the sun is not around as long.

•

Clouds – clouds reflect the sun's rays so the day is not as warm and the diurnal variation is less. The diurnal variation will be much decreased when both the day and night are cloudy.

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•

Altitude – mountains cool more rapidly after the sun goes down, because they are heated less in the first place by the sun.

•

Humidity – water in the air absorbs heat and gives off heat. What this means is that warm and humid areas will have a decrease diurnal variation in temperature compared to drier areas on the earth.

•

Wind speed – if it is windy, cold and warm air will mix, which will decrease the diurnal variation in temperature.

Now that you know what the differences are temperature between night and day, let's look at regional temperature variations throughout the world.

REGIONAL TEMPERATURE VARIATIONS IN THE WORLD When we talk about regional temperature variations, we usually mean climate changes.

There are several different climates on earth that are affected by several factors. Climate is defined as the average of the weather conditions in a certain place over a minimum of 30 years. In most cases, it is hotter at the equator and colder at the poles, however, other factors do come into play. While temperature does affect climate, other factors include the amount of precipitation received in an area as well as when this precipitation is received.

These are the basic 5 climates on earth: •

Dry – this is obvious. These are parts of the world where there is very little moisture, and what moisture there is will be evaporated quickly evaporated from the air.

•

Tropical – these are areas mostly around the equator. The average temperature will be greater than 64 degrees Fahrenheit throughout the year, humidity levels will be high, and precipitation exceeds 59 inches of rain per year.

•

Temperate – these are areas of the world with more men humid summers, thunderstorms in the summertime, and relatively mild winters.

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•

Continental – in these regions the summers may be warm or cool are very cold.

You can expect wintertime temperatures to be below -22 degrees Fahrenheit (-30 degrees Celsius) and heavy snowstorms in the winter months.

•

Polar – these are very cold areas on the earth with temperatures in the summer rarely exceeding 50 degrees Fahrenheit or 10 degrees Celsius. These areas are obviously closer to the North and South Pole.

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This image shows the different climate regions on earth.

You need to know that the distance from the equator is only one aspect of climate. You need to consider several other factors that affect what type of climate you live in. These include the following: •

Latitude – of course, because latitude and temperature are interrelated, this will play a major role in the climate and temperature you have in your region.

•

Location related to major bodies of water – if there is a large continental region, the areas near the center of the region and away from larger bodies of water will have wider variations in temperature with the seasons.

•

Nearness to mountains – we'll talk more about this later, however, you need to know that there will be differences in climate depending on which side of a mountain you live.

•

Altitude – altitude affects both precipitation and temperature, so certainly this will affect the climate in the region.

•

Ocean currents – we will talk a lot more about this later, however, ocean currents will drag in warm winds at affect the climate in a region over a long period of time.

Knowing the climate you live in will affect the types of plants you grow in your farm or garden. For example, you would need to decide your specific climate region in order to decide which type of apple trees you wanted to grow. You would also have to know whether or not you could grow palm trees, peach trees, or many agricultural crops based on your climate region. A good example of how this works is a map of the plant hardiness zones in the United States. Gardeners and farmers use this religiously.

THE EFFECTS OF ALTITUDE ON TEMPERATURE Certainly, altitude affects temperature; it is a bit more complicated than we have previously talked about, however. The people who study this the most besides meteorologists are people like hikers and skiers. They look at a mountain and the

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prevailing conditions to determine what to expect as they increase their altitude. A rule of thumb they often use is this: •

Sunny day – if there is no precipitation or cloud cover the temperature will decrease approximately 5.4 degrees Fahrenheit for every 1000 feet of elevation you go up. This is equivalent to nearly 10 degrees Celsius per 1000 meters.

•

Precipitation day – if you are in the cloud or there is precipitation, the decline in temperature with elevation will be less. You can expect a decrease of approximately 3.3 degrees Fahrenheit for every 1000 feet increasing elevation.

This is about 6 degrees per 1000 meters.

The reason why precipitation decreases the effects of elevation is because precipitation increases humidity. Humidity adds to the air pressure so the air is less dense. Less air pressure differential and less density differential means the temperature will not decrease as much when it is precipitating on a mountain.

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KEY POINTS IN THIS CHAPTER •

There are many different types of thermometers used to measure temperature in various ways around the globe.

•

In general, you should measure your backyard temperature approximately 5 feet above the ground and in the shade.

•

Diurnal variations in temperature exists everywhere but in varying degrees depending on the climate and other conditions.

•

Temperature variations in regions depend on the overall climate. Climate itself depends not only on temperature but in the quality and quantity of precipitation in the region.

•

Altitude almost always results in a reduction in temperature, however, this will vary depending on the amount of precipitation and humidity in the air.

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CHAPTER THREE: QUESTIONS: 1.

When you stand outside and feel the temperature, what are you actually feeling? a. Temperature of the molecules and atoms in the atmosphere b. Kinetic energy and density of atoms and molecules in the atmosphere c. Electromagnetic radiation left over from the sun's rays or due to the sun's rays. d. Radiating heat from the earth's surface

2.

For every degree Celsius rise in temperature on a thermometer, how many degrees Fahrenheit will this kind of thermometer increase? a. 0.6 degrees b. 1.0 degrees c. 1.8 degrees d. 2.3 degrees

3.

You are checking the weather and want a good temperature reading outdoors.

Which reading do you most trust to be accurate in your immediate vicinity? a. Your automobile thermometer b. The thermometer hung under a shade tree in your backyard c. The bank thermometer down the street d. The thermometer on your patio

4.

Official thermometers used by the US weather service are generally how far off the ground? a. 1 foot b. 3 feet c. 6 feet d. 12 feet

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5.

Which thermometer used depends on the differential expansion of two metallic objects with temperature changes? a. Thermistors b. Liquid in glass thermometers c. Bimetallic thermometer d. Platinum resistance thermometer

6.

What is the main advantage of sonic thermometers? a. They are cheap to make b. They are small and compact c. The temperature is easy to determine as the sensor is insensitive to most things. d. They are not sensitive to sun exposure

7.

What is the main advantage of the heated probes used on airplanes to measure air temperature? a. They do not need to be calibrated as often as other probes b. They are resistant to supercooled water vapor in the upper atmosphere c. They protect the platinum resistance wires from breakage d. They are more accurate and faster than non-heated probes

8.

If you have a thermometer and checked the temperature around you, at what height above the earth during the daytime would you get the highest temperature? a. One centimeter above the ground b. One foot above the ground c. One meter above the ground d. 3 meters above the ground

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9.

In general, how long must a weather pattern be stable for it to be called a climate change? a. 10 years b. 30 years c. 60 years d. 100 years

10.

Knowing what you know about temperature and climate, what climate region would you say that most of the United States exists in? a. Dry b. Tropical c. Temperate d. Continental

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CHAPTER 4: HUMIDITY, CLOUDS, AND CONDENSATION This chapter is essentially the study of hydrology or water in the environment. Besides the temperature, you usually want to know what if any precipitation there is outside.

This chapter introduces the basics of how precipitation can form. You will learn what the different phase changes of water are called and what they look like in terms of the weather. After you read this chapter, you should have a clear understanding of why we have dew on the ground, foggy weather, and clouds in the sky.

EVAPORATION, CONDENSATION, AND SATURATION Chemically-speaking, water is in a class by itself. It is a small polar molecule, which means it can easily dissolve salts and most all biological molecules, except for lipids. It is the perfect medium for life on earth. It is a strange substance, however, because it can exist in all of its three main phases at once and because it Is less dense as a solid so ice can form on lake surfaces but not at their bases.

Most of the earth's surface is water – about 71 percent – and there are more than one billion cubic kilometers of the stuff in the different bodies of water on earth. About 97 percent is free water in the oceans, with the rest found in the polar ice caps, freshwater sources, or in the groundwater beneath our feet. Only 0.03 percent of the water on earth is atmospheric water.

There is a water cycle or hydrologic cycle on earth, where water goes from the different phases and in different parts of the planet. This cycle is shown in figure 13.

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Figure 13.

As you can see by the image, there are many facets to the water cycle. Water precipitates in its many forms. It lands everywhere and infiltrates the ground. It then percolates or travels through surface flow or snowmelt into rivers that ultimately dump into the ocean. From there and all over the earth, water then evaporates back into the atmosphere, where it then condenses to make clouds that deposit or precipitate the water back to earth. Plants also transpire water as part of their processes, also sending up water from earth to the sky.

What do all of these processes really mean on a microscopic or cellular level? We should define these first: •

What is evaporation? This is where liquid water becomes gaseous water. It does not need to happen at the boiling point of water. Water will evaporate at much lower temperatures than that.

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•

What is condensation? This is the reverse of evaporation and happens when water vapor becomes liquid water. Dew formation is an example of this process.

•

What is transpiration? You can think of this as plants sweating. Plants will have water close to the tops of their leaves. As the sun warms the leaves, they sweat water, which then evaporates naturally into the air. This water is released by the leaves as part of their water transport processes.

•

What is sublimation? Sublimation is the process where ice becomes gaseous water vapor while skipping the liquid phase. This is seen when your ice cubes give off steam or when those in your freezer shrink over time.

Water enters the atmosphere in one of 3 ways: evaporation, transpiration, and sublimation. Among these 3, evaporation is the largest contributor by far. In terms of transfer of water from the atmosphere to the earth and vice versa, you have evaporation and precipitation as the major players. You should know that over a year's time, there is very little change in the amount of water in both the atmosphere and on the ground.

Certainly, things can get off balance as the years progress.

How long do you think any given water molecule takes from the time it is evaporated up into the atmosphere until it ends back on earth again? It takes an average of 11 days for this to occur. The water molecule will need to condense into a cloud droplet and then fall as precipitation from a cloud.

Water that is in a liquid or solid form on earth lasts much longer than a gaseous water molecule in the atmosphere. Any given water molecule will last for 2800 years somewhere on the earth before it evaporates. Imagine how long a water molecule in a glacier must stay before evaporating. It can be tens of thousands of years, depending on the climate and the size of the glacier.

Both evaporation and condensation rely on the kinetic energy of water in its various phases. What happens in evaporation, is that surface water gains enough kinetic energy to essentially break away from its liquid surface and enter the air. There are several factors that can control the rate of how this happens. First, you need to have some surface area on the water's liquid surface so that the molecules can come in contact with the surrounding air. Next, you need some heat energy. You do not need the energy it 3

takes to boil water – only enough energy to break a few molecules away from the water surface. Third, the presence of wind or air movements helps accelerate the evaporative processes. Fourth, if there are already a lot of water molecules or other evaporating substances in the air, this will inhibit evaporation.

Exactly how much energy does it take to do this? It turns out that it takes only 80 calories per gram of energy to take solid ice and melts it. It takes 600 calories per gram of water, however, to evaporate this water. Sublimation takes the most energy, at 680 calories per gram. You will note that sublimation takes the equivalent of the energy to first melt and then evaporate water. The reverse of these processes, condensation, freezing, and deposition, all involve lower energy states being achieved. Figure 14 shows these energy differentials.

Figure 14.

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As you can imagine, the amount of energy it takes to undergo a phase change is identical to the amount of energy gained by going back to the phase again. No energy is gained or lost in the process. For example, in condensation, there is a release of energy known as the "latent heat of condensation". What does this heat do? Actually, it warms the air around the condensed spot. So essentially, evaporation takes energy, while condensation releases energy. This is why, when you are in a hot pool swimming, evaporation cools your skin. Energy is taken from your skin to undergo the evaporative process, and you are cooler.

This interesting process of evaporation also explains why you have a sudden drop in temperature just before it begins to rain during a thunderstorm. Why would this be?

The early droplets from a thunderstorm are small and evaporate easily. You do not feel them, however, you do feel the effects of the fact that they have evaporated. They have taken energy from the air to do this, resulting in cooler air. Amazing, isn't it?

Another thing you need to know is that it is rarely possible to have only evaporation happening without some condensation happening. These are never-ending processes that are continually happening, so what you notice is a net change of either evaporation or condensation. For example, if you have 3 water molecules evaporating for every one molecule that is condensing, you will have some degree of net evaporation in the positive direction.

Let's look at the factors that control the condensation rate. These are often similar to those that control evaporation. You first need to have a surface area to work with. Then you need to have some water vapor molecules in the air. Unlike evaporation, you do not want a lot of wind to be happening. You also want a situation where the air is cooling over time.

Now that you know that condensation and evaporation occur simultaneously, it should not be hard to understand the concept of relative humidity. You will hear talk about the relative humidity on any given day. You probably know that a higher relative humidity means it will be more humid outside. The reverse is true when relative humidity is low.

The calculation for relative humidity is easy. You simply take the rate of condensation, divide this number by the rate of evaporation, and multiply the ratio by 100 percent. A

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relative humidity of 100 percent is the maximum that will be reported; however, you can get a higher relative humidity than this. You can expect it will be raining at this time.

Meteorologists do not really do this calculation as it would be too cumbersome. Instead, the relative humidity is determined by the dewpoint of which can help say how much water vapor is in the air higher dewpoints mean higher rates of condensation. So, what is dewpoint?

The dewpoint is a temperature you can determine that will say how much the air needs to be cooled in order to have 100 percent relative humidity. At the dewpoint, the air is saturated with water molecules in vaporized form and can hold no more. This temperature is when you will start to see precipitation, dew, or fog.

Meteorologists often use the dewpoint to tell you how comfortable you will feel. For example, if it is 30 degrees outside and the relative humidity is 100 percent, the dewpoint is also 30 degrees. Will you feel as though it is hot and muggy outside? Not really. On the other hand, if it is 70 degrees outside and is also 100 percent relative humidity, the dewpoint will be far higher at 70 degrees you will feel this as being muggy.

Note: the air needs to be cooled at constant pressure in order to determine the dewpoint.

When you hear or report the dewpoint, you can expect certain things out of that number. For example, a dewpoint of less than or equal to 55 will feel comfortable and even dry outside. A dewpoint between 55 and 65 would indicate a day that was somewhat muggy in the evening. Any dewpoint greater than 65 degrees would be extremely muggy throughout the day.

While there are online calculators for determining the dewpoint given the temperature and relative humidity, this is a calculation that would be difficult to do simply. You can certainly estimate it, however, the actual calculations are complex and based on a number of factors beyond the scope of this course.

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DEW Now that you know what relative humidity and dewpoint mean, let's look at the situations in the environment where dew forms. When you think of dewpoint, you might think of numbers like 50 degrees or 65 degrees, when in reality you can have dewpoints as low as -50 degrees Fahrenheit. Under such conditions, the air is very dry and bitterly cold. There are few water vapor molecules in the air at all. This is why you might experience itching and skin dryness in the wintertime. There just isn't any moisture in the air for your skin to feel moist.

The highest dewpoints around the world are found in the warm and moist tropical areas, particularly near large ocean bodies. You may rarely see a dewpoint in the continental United States higher than the low 80 degree mark. Believe it or not, there are some parts of the world where it is not unusual see dewpoints higher than 90 degrees on occasion.

You can look at any dewpoint chart or map to see where in the world it is more moist or more dry.

In the United States, higher dewpoints are in the southeastern part of the continental US. This is because of warm and moist air masses coming up from the Gulf of Mexico or from the Atlantic Ocean. In the summer months, when it is warm, the evaporation rates are high and there is a great deal of moisture in the air. In the southwestern United States, you will have high heat but no source of moisture to draw upon. The temperature will be high but the dewpoint will be low, so the relative humidity is low. This type of heat tends to be more tolerable to the human body.

Why would you feel so uncomfortable in muggy air? This is because your body really relies on evaporation to cool itself. When the concentration of water vapor in the air is high and your body is exposed to higher temperatures at the same time, you will not be able to sweat as effectively and you will feel warm and very uncomfortable.

In clouds for example, the relative humidity might be greater than 100 percent. This is because warm air has risen into the cloudy area where it is now cool. If the air that has risen is full of water vapor, this cooled air will now condense, leading to droplets of

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water in the clouds. There are tiny condensation nuclei within the clouds that have warmed the surrounding air. Remember, condensation gives off heat.

The phenomenon of dew is simply condensation that generally happens on the ground or low-lying areas when the moisture laden air cools during the night. This cooler air means that the temperature approaches the dewpoint so that, in the specific areas where dew forms, the dewpoint and temperature are equal and condensation is favored. Calm and cool nights after warm humid days are the most likely result in morning dew the next day.

Cold days also prevent dew formation. If the temperature falls below freezing, of course you will not get dew on the ground. Instead, you will get sublimation or a water vapor to ice transformation. You may have seen a phenomenon known as hoar frost before. Hoar frost is seen when water vapor is deposited in solid form directly on branches of trees, grass, and other areas when the conditions are right. Optimal conditions are temperatures below 32 degrees Fahrenheit and high humidity. You often see hoar frost when it is foggy outside in the wintertime, particularly in the morning. This type of frost is different from black frost, which occurs when the tips of the leaves of plants freeze.

FOG it would be easy to say that fog is just clouds on the ground, but it is more complicated than this. Fog is different from mist mostly because of its density. Fog is a collection of condensed water droplets that reduce visibility to less than one kilometer. Mist is similar to this, however, the visibility is usually not as reduced and can be up to 2 kilometers away.

We will talk about condensation nuclei in a minute. What these are, however, are collections of dust or air pollution that allow for water vapor to condense around them.

In other words, water vapor does not just materialize without something to stick to. Sea fog or fog that occurs over salty water involves water vapor that has condensed around solid pieces of salt above the ocean surface.

You need 3 conditions to make fog. First, you need some type of dust, pollen, or dirt that serves as condensation nuclei allowing for the water vapor to collect in the first place.

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Second, you need conditions where the spread between the temperature in the dewpoint is minimal or near zero. These would be considered high humidity conditions. Third, you need some type of light surface winds causing more air to come in contact with the ground, but not high winds that would brush away the fog completely.

TYPES OF FOG Believe it or not, there is more than one type of fog. Ask any pilot or student of aviation and they will tell you the effects of these different types. Let's look at what they are: •

Radiation or ground fog – this is a relatively flat kind of fog extending less than 20 feet off the ground. You will see it in very low-lying and flattened areas on clear nights with little wind and high humidity. As you remember, the ground will cool during the night until the air just above it reaches the dewpoint. If the night were cloudy, you would not get this type of fog because the radiation of heat from the ground will be blanketed by these clouds. The fog will dissipate in higher winds and certainly when the sun rises. In order for it to disappear the surface temperature must rise enough to accommodate the moisture.

•

Advection fog – this happens when warm and moist air flows over a cool round surface. You need wind velocity to have this kind of fog, which actually becomes thicker and more dense as the wind speed increases. This type of fog may form over water and last for several weeks. It often rolls over land in the latter part of the day and rolls back over water in the morning. You might see this in the Gulf Coast when tropical air moves over older ground or in the Pacific Ocean when cooler water rises to cool the air above the ocean. It is very thick and somewhat more resistant to solar radiation than other types of fog.

•

Upslope fog – this is the type of fog you see when wet and stable air is forced upward along a slope. At some point, the air reaches hundred percent humidity and sufficient cooling to allow for condensation. You need wind to create this type of fog, which often forms along the slopes of mountain ranges in North America in the winter months.

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•

Evaporation fog – this type of fog happens strictly due to evaporation of moist air as it mixes with cooler and drier air. There is steam fog, which happens when cold air moves over warmer water. The cold and warm air mix and together reach 100 percent humidity. This is when the fog forms. You often see this is wispy smoke coming off of a water's surface. There is also frontal fog, which happens when warmer raindrops evaporate near the ground forming a high humidity situation and fog.

•

Ice fog – this type of fog only occurs in cold weather. The temperature is far below freezing in the fog is actually sublimated ice crystals the conditions are identical for regular fog formation with the exception that the temperature is often below 25 degrees Fahrenheit at the time.

•

Valley fog – this is an obvious name for fog trapped in the valleys between mountains, prevented from escaping because of its density. Valley fog has been known to be deadly, in part because it can trapped air pollution in low-lying valley areas. In one case, more than 60 people died from Valley fog in Belgium in 1930.

CLOUD FORMATION AND CLOUD TYPES By now it shouldn't be too hard to figure out how clouds form. These are situations where there is net condensation compared to evaporation. The basic recipe to make a cloud includes 3 ingredients: 1) some type of moisture; 2) aerosols in the air; and 3) cooling of the atmosphere. The moisture part comes from water vapor, which condenses into clouds. Aerosols are the dust, dirt, air pollution, or salt to about condensation nuclei. Again, it is difficult to have water droplets condense out of thin air.

Research has shown that it would take approximately 400 percent humidity to have water vapor form in the absence of condensation nuclei. These nuclei are not the same as the flat surface you see when condensation forms on the ground for example; however, each small particle has a surface area upon which a water molecule can condense. Very tiny particles actually have quite a large surface area when they are added together. Many condensation nuclei are called hygroscopic, because they attract

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water vapor and help initiate condensation. It still takes a relative humidity in the range of 100 percent or slightly greater to get condensation to happen in a cloud.

Lastly, of course, you need some way of cooling the air in order to have net condensation. Cooling slows the water molecules in gaseous form down so they can begin the huddle together and condense. It is possible to cool air simply by lifting it up into the atmosphere. If you take warm air laden with water and allowed to rise to higher altitudes you will get cooler air that can no longer hold such large amounts of water. If the conditions are right, clouds will form as a result.

Consider a parcel of air near the ground that rises. This air will be more dense than surrounding parcel air. In order to balance the densities out, the air will expand due to the kinetic energy of the warm and dense air molecules. The kinetic energy, as it gets spent, cools that parcel of air and results in its relative humidity being slightly greater than 100 percent. By slightly greater than 100 percent, we mean in the range of 100.1 to 100.2 percent (in other words, not very much). Still, it is enough to cause net condensation.

On the other hand, air that sinks will dissipate clouds. If air becomes too heavy and sinks into the atmosphere for the ground there will be more evaporation and the cost will dissipate. What this means is that when it is warm and air is dense, the air will sink evaporation dissipates the clouds.

There is an interesting type of cloud called an orographic cloud, which forms because of differences in the terrain of the earth. Wind can blow up to a mountain but cannot go through it. As it ascends the slope through what is called orographic lifting, there will cool. If this air is humid enough, clouds will form along the slope of the mountain, resulting in extremely rainy and snowy areas on the Windward side of mountains. As you can imagine the leeward or less windy side of the mountain would be quite dry in comparison.

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TYPES OF CLOUDS in reality, there are more than 100 types of clouds. For all practical purposes, however, you need to memorize just a few. You would not be a good meteorologist at all if you could not look in the sky and say the type of cloud you see. Let's get at it: You first need to know that there are 3 major categories of clouds: •

Upper level clouds or high level clouds – are between 5 and 13 kilometers above the earth. The 3 main upper level clouds are the cirrus, cirrostratus, and cirrocumulus clouds.

•

Mid-level clouds – these are clouds between 2 and 7 kilometers above the earth. These are the altocumulus, altostratus, and nimbostratus clouds.

•

Low level clouds – these are clouds between zero and 2 kilometers above the earth. You know them as cumulus, stratus, stratocumulus, and cumulonimbus clouds.

Figure 15 shows you the different types of clouds you might see:

Figure 15.

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HIGH-LEVEL CLOUDS Let's talk about the high level clouds first. The cirrus cloud is very common. They are thin and wispy clouds high in the sky. Because of their height, there are many ice crystals in this type of cloud. You often see them as red or bright yellow during times of sunrise and sunset.

Cirrocumulus clouds are lovely. These are small and puffy clouds you'll see spread out throughout the sky. They can have a gray coloration and look like altocumulus clouds without the darkish shading. When you see this cloud pattern, expect to see them ahead of a warm front.

Cirrostratus clouds are also high in the sky and are spread out like sheets or a blanket in the sky. You can easily see through them, especially on moonlit nights. If you see them as white rather than light gray, you can expect they hold moisture and are also signaling the presence of a warm front. The ice crystals can form what you see as a halo around the sun or moon. If these get lower in the atmosphere, they are called altostratus clouds.

If you see them floating westerly, it signals a warm front rainstorm.

MID-LEVEL CLOUDS The altocumulus clouds usually appear in clumps or groups. They can be medium-gray to white in color. Because they are lower level compared to those we've just discussed, they have mostly rain particles with a few upper-level ice crystals. You will also see these when a warm front is coming and when seen with other kinds of clouds, you can expect a storm. Light to moderate rain comes from these types of clouds.

Altostratus clouds are considered rainy day clouds. Look for large stretches of thick clouds blanketing the sky for thousands of square miles. There is often light rain or snow coming from these types of clouds, but do not expect heavy rain unless they merge into nimbostratus clouds. These are depressing-looking gray and featureless clouds, often indicating a warm-front rainstorm.

Nimbostrati are probably well known to you as heavy rain clouds. The term nimbus means "rain" in Latin and whenever you hear it's a stratus cloud, it means it is spread

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out. These are dark and ominous, blocking out the sun to a significant way. You can see them sometimes drop low enough to be low-level clouds. Wet air in a warm region rises and condenses to form these clouds. Some nimbostratus clouds will come from higher level altostratus clouds that then descend to be these types of rainclouds.

LOW-LEVEL CLOUDS Stratus clouds are thin and spread out. They look like fog in the sky and can actually descend to form real fog. They stretch out horizontally – made from large masses of air that rise and condense into water vapor-laden clouds. They do produce rain or snow but it is usually light snow or rain.

You know cumulus clouds as puffy, cotton-like clouds that mean good weather, even if they do occasionally produce some rain. These are common clouds that are seen everywhere in the world.

Cumulonimbus clouds are also puffy and white but are much bigger than regular cumulus clouds – reaching as high as 8 kilometers into the air. You might call them "tower clouds", making them clouds that extend from low to high levels. Of course, this means it has both water crystals and ice crystals. Rain will be intermittent but can come on as downpour. They are harbingers of thunderstorms. Look for these in the springtime or summertime afternoons.

Stratocumulus clouds lie low in the sky and spread out like a fluffy cotton blanket. They are similar to cumulus clouds except they are much bigger. The base is flat from lower windshear but convection leads to puffiness of the upper layer. Look for grayish tones in these clouds. They look ominous but release little in the way of major rain.

You need to know that these ten cloud types are just broad categories of clouds. They are normally not terribly important except for a few that many meteorologists refer to. One example is the cirrus uncinus, which is a cirrus cloud with a hook on it. The famous mammatus clouds or mammary clouds look like multiple hanging breasts.

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KEY POINTS IN THIS CHAPTER •

Condensation, evaporation, and sublimation are common phenomena in whether systems.

•

The water cycle or hydrological cycle is important to life on earth and to the weather.

•

You should understand the concepts of dewpoint, relative humidity, and how to calculate these.

•

Dew and fog are common things you'll see in meteorology related to a predominance of condensation over evaporation.

•

Clouds form as air cools or rises, with moist air in them condensing around condensation nuclei.

•

You cannot really have clouds without the presence of condensation nuclei in the atmosphere.

•

There are many different kinds of clouds with certain features that distinguish them in terms of their shape, their size, and their potential for precipitation.

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CHAPTER FOUR: QUESTIONS 1.

In the world's hydrologic cycle, you have many aspects. What is the major source of transpiration in this cycle? a. Oceans b. Lakes c. Snowmelt d. Plants

2.

What type of process is involved in dew formation on the grass on the morning? a. Condensation b. Evaporation c. Sublimation d. Percolation

3.

Where on earth will you find the least amount of existing water? a. In the polar ice caps b. In the groundwater c. in the atmosphere d. In the permafrost

4.

Which phase change in water results in the highest increase in kinetic energy of the water molecule in order to achieve the phase change? a. Sublimation b. Deposition c. Condensation d. Melting

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5.

You look outside the temperature is 55 degrees. You check and see that the relative humidity is about 95 percent. What would you estimate the dewpoint to be? a. 65 degrees b. 54 degrees c. 46 degrees d. 73 degrees

6.

At what dewpoint in the air would you feel an extremely oppressive humid environment? a. 45 degrees b. 50 degrees c. 58 degrees d. 65 degrees

7.

What type of fog is seen at the base of mountains? a. Advection fog b. Upslope fog c. Ice fog d. Radiation fog

8.

Which type of fog tends to roll in along the shores at night and back out to the ocean during the daytime hours? a. Advection fog b. Upslope fog c. Ice fog d. Radiation fog

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9.

When you hear a cloud with which root word in its name, you can expect it means rain is going to be present as part of the process? a. Nimbus b. Stratus c. Cirrus d. Cumulus

10.

When you hear of a cloud with this root word in its name, you can expect it means the clouds are widely spread out? a. Nimbus b. Stratus c. Cirrus d. Cumulus

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CHAPTER 5: CLOUD FORMATION AND HOW PRECIPITATION HAPPENS In this chapter, we will introduce you to the subject of atmospheric instability and how this contributes to cloud formation and precipitation. In truth, the atmosphere is never completely stable but there are times where there are long stretches of weather without rain or even clouds. We will also talk about how clouds form precipitation and how they form the type of precipitation you see that falls on the ground.

ATMOSPHERIC STABILITY Believe it or not, there are times when the atmosphere is far more stable than others. In meteorology, the concept of atmospheric stability is equated with balance or lack of immediate change. Atmospheric instability, on the other hand, is equated with significant change, such as thunderstorms, hurricanes, or tornadoes.

With regard to the weather, need to think of more than 2 types of stability. When we talk of stability, we mean the stability of air parcels or collections of air in the atmosphere.

Consider these 3 conditions: •

Unstable – in this case, the parcel you are talking about is warmer than the surrounding air. As you know, this means that air will rise. It is not stable.

•

Stable – in this case, the parcel air is colder than the surrounding air. This air will sink. Because of its lower energy level and sunken state, it is called stable.

•

Neutral – in this case, the parcel of air has the same temperature as its surroundings. It will not sink and it will not rise.

So you can see that the concepts of stable, unstable, and neutral do not always mean what you would expect them to in meteorology.

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Air parcels are not really all that complex. They are masses of air that have the same characteristics and that generally travel in the same direction as a cluster. You can call them air masses or air clusters or air blobs. Air does not move within an air parcel, but when it does this, it is called adiabatic process. Adiabatic processes are reversible and involve no heat exchange. In fact, the term "adiabatic" means that the temperature remains the same.

Consider any parcel of air with a certain pressure and a certain temperature. If you could physically lift this air parcel, it would be in a situation where all of its surrounding environment was all a lower pressure, mainly because of the higher altitude. Your imaginary air parcel has more pressure in it than the air around it so it will naturally expand because of course it has no real walls. In order to do this, energy is taken from the air molecules and it will naturally cool down the air parcel.

Suppose you can take this same air parcel and now move it downward toward the ground. Here it is surrounded by warmer air under higher pressures. Under these pressures, it must contract. As it contracts, the molecules are closer together and because of this, the air parcel will be warmer. It would be the same as if you took a number of people on a cold day and smash them together into a small huddle of people.

Everyone would warm up. This process is also adiabatic because no heat is exchanged between that air parcel and the surrounding environment.

Think about it. This is different than what you would see if you mixed two air masses of different temperatures, averaging their temperatures afterward. In this case, there is no mixing. The temperatures change only because of a change in the kinetic energy of the air parcel itself. Even though an air parcel has no walls, you can think of it as truly being a bubble of air.

WHAT IS THE DRY ADIABATIC LAPSE RATE? Parcels of air have varying degrees of relative humidity. If the relative humidity of any air parcel is less than 100 percent, the temperature change you see with rising and falling air masses will be a constant temperature. This constant temperature downward with height is called the lapse rate. Meteorologists also call it the dry adiabatic lapse rate

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if there is no humidity in the air parcel. This dry adiabatic lapse rate is approximately 10 degrees Celsius per kilometer; in actuality is precisely 9.8 degrees Celsius per kilometer.

Again, this is predicted by decrease in the internal energy of the expanded air mass.

If the environment in an area is considered neutral from a meteorology perspective, air masses neither rise nor fall. In any unstable equilibrium situation, however, air parcels will either rise or fall, although rising is more common than falling. How do you know if the air mass or air parcel is stable? Let's look at this.

Consider an air mass that has just moved. You will know if it is stable by checking the temperature and pressure of the air around it. If you lift this air parcel it will cool and, if it cools to a degree greater than its environment, the air will be denser and will fall back to where it was. This is a stable air mass because it resists being moved vertically. On unstable air mass will not resist this and will rise to whatever level its own temperature matches the environment. Again, it is mainly the temperature of an air parcel that predicts where it reaches equilibrium. You will know if the air parcel is stable or not by checking the temperature of the rising air and of the environment at different altitudes around which the air parcel resides. As you can imagine, this process involves weather balloons and radiosondes in order to measure the vertical temperature at any given area. This process is called sounding.

We call any air parcel that is not completely saturated a dry air parcel. It is easy to measure its stability. If the environment involves a lapse rate that is equivalent to the dry adiabatic lapse rate, we know what happens to the temperature with elevation and we call this air parcel neutrally stable.

If the environmental lapse rate is less than the dry adiabatic lapse rate, the air parcel will either be lifted and colder than its environment or pushed down and warmer than its environment. In this situation, the air mass is still stable; it will have an average tropospheric lapse rate of approximately 6.5 degrees Celsius per kilometer. On the other hand, if the environmental lapse rate is greater than the dry adiabatic lapse rate, this air parcel will be warm on elevation compared to its environment and colder if it is pushed down compared to its environment.

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MOIST ADIABATIC LAPSE RATE Of course, the dry adiabatic lapse rate does not work if the air is moist. Remember the saturation level of any air mass depends on its temperature and its moisture content.

Lower temperature air masses have less moisture saturation. What happens then is that an air parcel laden with moisture that rises and cools will not be able to hold that moisture. Under the right conditions, a cloud will form.

Remember too that condensation draws energy from the area because it takes energy to condense something. The latent heat of condensation is approximately 2260 kilojoules per kilogram or with respect to water, about 40.8 kilojoules per mole. This means that some of the adiabatic cooling you get when its air mass expands is offset and doesn't cool as much as you would expect. This slower rate of temperature loss is called the moist or wet adiabatic lapse rate. It is only 4.5 degrees per kilometer because condensation adds heat to the air mass. Figure 16 shows you what this looks like:

Figure 16.

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This brings us to trying to understand what it means to have a stable or unstable air mass situation. An absolutely stable atmosphere is when the environmental lapse rate, or the actual lapse rate is less than the moist adiabatic lapse rate. The air parcel that is rising is cooling faster than the environment even during saturation. The air mass is prevented from continually rising.

An absolutely unstable atmosphere is when the environmental lapse rate or the rate of temperature reduction with elevation is greater than the dry adiabatic lapse rate. The air may be saturated or unsaturated but it cools at a slower rate than the environment, so always be warmer and will always continue to rise.

Finally, there is the conditionally unstable environment, where the environmental lapse rate is somewhere between the wet and dry adiabatic lapse rates. Exactly what happens depends on how saturated the air is with moisture. If the moisture levels are high, it will cool closer to the rate we see in the wet adiabatic lapse rate, and you will get continual rise of the air parcel.

You can often plot the rate at which an air parcel cools with elevation, noting that at some point the air parcel will become completely saturated. What happens then? This is when and where clouds form. The term Lifting Condensation Level or LCL is this level at which a dry adiabatically lifted air parcel is saturated. You can follow the temperatures as the altitude rises in the air parcel to where it becomes warmer than its environment while it is rising along the moist adiabatic lapse rate line. At the appointed time it becomes warmer than its environment, you would call this the Level of Free Convection or LFC. Further above this, the air parcel will suddenly become cooler than its environment. This is called the equilibrium level or EL.

CLOUDS AND CONVECTION Now that you have some idea of how air moves, rises, and falls, you should be able to better understand exactly how clouds form in more detail. Clouds as you know are collections of suspended water or ice particles somewhere in the atmosphere. While these suspended particles do have weight and do fall from the sky, while in a cloud their mass is so small they are in effect suspended.

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There is a diagram called the Clausius–Clapeyron diagram. What this shows you is the saturation level of air different temperatures. It is not a linear relationship. Figure 17 shows you the exponential relationship between pressure and temperature when it comes to air saturation:

Figure 17 This Diagram shows you different ways that clouds can form in the atmosphere. As you can see, you can plot the saturation point at which clouds will form just by looking at the temperature. Knowing what you know about air parcels, you can determine 3 possible ways a cloud might form. For example:

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•

You can add moisture to the air parcel. You do this every time you exhale on a very cold day. You can also see it from cooling towers, contrails, and sea smoke.

Contrails you see all the time are simply condensation or vapor trails from aircraft.

•

You can also remove heat from an air mass. At night time, especially on clear nights over land areas, you will get radiation fog from cooling just above the ground surface. Evection fog comes from air that moved over oceans, cooling the air as it flows, forming fog. These fog types involve cloud formation due to heat removal.

•

Cooling by means of adiabatic expansion is essentially what we've been talking about as the 3rd option. In this case, you have upward movement of an air parcel that cools to the point of condensation. You can also see it along aircraft wing tips or near tornadoes when vortices form.

You already know that clouds cannot form without a place for the water droplets to collect. These places are called cloud condensation nuclei or CCN; these are of course the aerosols found everywhere in the atmosphere. You can imagine that places having carbon dust from fires, volcanic activity, or even sea salt crystals above the ocean are those with a lot of these condensation nuclei in them.

Have you ever heard of cold clouds? Clouds with this name are made from ice crystals.

These ice crystals are caused by special nuclei called ice nuclei. Dust in the atmosphere often is a nucleus for ice to form. Meteorologists use silver iodide to seed clouds in this way.

You can define a cloud by the water phase inside it. Warm clouds have only water droplets in them made from ice crystals. Cold clouds often look fuzzy around the edges and are almost always of a higher altitude. There are also mixed phase clouds that of course have both water and ice crystals as part of the cloud. High clouds such as tower clouds are often mixed phase clouds with both ice and water in them at different altitudes.

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HOW PRECIPITATION FORMS While everyone has experienced precipitation, few people understand how it forms the different names for precipitation. Let's discuss the different kinds of precipitation and how they happen.

Of course, precipitation falls often in the form of rain. Have you ever wondered why some rain is gentle with small misty raindrops, while other rain is literally a downpour with giant raindrops? Why do you see some clouds that look like rain is coming, but they don't rain at all? Actually, the average raindrop inside a cloud is only 20 micrometers in diameter. This is very small. The raindrops you feel are nowhere near that small; there are reasons for this that we will discuss.

The average raindrop you feel will be about 2 millimeters in diameter. This is literally 10,000 times the size of the average condensation nucleus. If you measure the size of a cloud droplet, a raindrop will be 100 times its size. The size of a raindrop can be as little as 0.2 millimeters or as large as 2.5 millimeters in diameter. This is why you feel such a difference when you feel drizzle as opposed to a downpour. You can imagine that a raindrop will grow in size inside the cloud until it becomes too heavy. Friction caused by the air itself will cause the raindrop to break up, with several smaller droplets falling to the earth. In other words, while cloud droplets have a negligible fall velocity, raindrops do not and they will fall.

The aerosol that causes water vapor to condense must be hygroscopic. The term hygroscopic means it loves to attach to water and absorb it. Salt particles above the ocean are very hygroscopic, so these will attract water vapor at the lowest humidity possible. Other particles are not as hygroscopic as salt.

There is an equation called the Stoke's drag law, which calculates the drag force and ultimately the velocity of any raindrop. The calculation indicates that the drag force and velocity of a raindrop is directly proportional to the diameter of the sphere, which is essentially the sphere of any raindrop. What you would see from this calculation is that it might take hours or days, if ever, for a cloud droplet to fall from the cloud to the ground. This is because the friction caused by air keeps it suspended within the cloud.

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Once the sphere becomes large enough, gravity kicks in and the raindrop has a terminal velocity, allowing it to fall. They simply need to be large enough to accommodate the air friction and the force of gravity on them.

So, how do raindrops get bigger in the first place? There are 2 theories to explain this.

The first is called the collision coalescence process. This works only for liquid rain. What happens is that smaller droplets collide and coalesce into a larger droplet. These are heavy and fall, colliding with even more raindrops. It is like a positive feedback loop, where raindrops just get bigger and bigger as they collide with one another, until they overcome the friction of the air that keeps them suspended and start to fall. It actually works best if there are cloud droplets of different sizes. Again, random collision and coalescence increases the raindrop size until it falls.

Interestingly, the very deep cumulus clouds make the biggest raindrops. This is because they have convection updrafts within them, allowing the raindrop to be suspended inside the cloud within the updrafts for a long period of time. These raindrops are the biggest when they fall. Stratus clouds are not very thick, so the droplets do not have the advantage of staying in the cloud very long. This will lead to drizzle or light rain rather than heavy rain.

If you do not live in the tropical areas of the world, you need to assume that a lot of rain clouds have ice in them. Unlike water clouds, clouds with ice in them do not just get bigger through coalescence. They must get bigger through another route.

Water freezes at zero degrees Celsius, however, there is such a thing as supercooled water which is liquid water colder than this freezing point. How can this be? It is similar to what happens with condensation and a lack of a condensation nucleus. Remember, the water must be very prevalent to coalesce without any nucleus. In the same way, cold water in liquid form can exist if there is no obvious ice nucleus to attach to. Liquid water can actually stay liquid at temperatures as low as -40 degrees Celsius. Any temperature below this level of -40 degrees Celsius means that water must be solid. In the range between zero degrees Celsius and -40 degrees Celsius, liquid water can persist as supercooled water.

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When it comes to the phase of water in a cloud, altitude is everything. At certain altitudes, water will be ice no matter what the conditions. As you get to lower altitudes, you can get what are called ice phase hydrometeors mixed with water droplets. A hydrometeors is any water droplet in any phase. An ice phase hydrometeors is basically a droplet of water in some solid form.

If you do get a situation where the temperature is below -40 degrees Celsius, you will get what is called homogenous or spontaneous freezing. It is most common above a large body of any kind of freshwater. These tiny droplets start as what are called ice embryos.

An ice embryo will by itself get large enough to be an ice nucleus. These lead to homogenous solid clumps of ice. Because it is so cold, these ice embryos do not move very much. If they would move too much, they would potentially break apart. By staying still, they can just get bigger.

Figure 18.

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Earlier, we mentioned that ice nuclei are simply cloud condensation nuclei in solid form.

They are similar to CCNs, but they need to be a certain geometry to fit into the shape of a proper solid clump of ice. Figure 18 shows you the shape of an ice crystal. It's this shape that ice crystals are more likely to attach to.

It is harder to find a good ice nucleus than it is to find a water vapor nucleus. For example, dust in the atmosphere is one of the best types of ice nuclei you can get. There are certain ice nuclei that allow water vapor to become solid as soon as they touch the nucleus. These are called deposition nuclei, because they allow the phase change to occur at the time they come in contact with the water vapor. This would involve deposition of gas into a solid without entering the liquid phase. Other nuclei attached water in the liquid phase and then freezes.

Small freezing nuclei in the clouds will take supercooled liquid droplets and turn them into solid droplets simply by colliding with them. This is known as contact freezing and the nuclei that do this are called contact nuclei. So, we have 4 different types of ice nucleation: •

Homogeneous freezing – this is freezing without any nucleus at all.

•

Deposition nucleation – this is freezing that goes from gaseous to solid without liquid water in between.

•

Immersion or condensation freezing – this is freezing on a basic ice nucleus.

•

Contact freezing – this is freezing through collision of water on an existing ice embryo.

Because of this super cooling process, you now have a lot of very cold water droplets and a few ice crystals in most clouds. None of these are very heavy by themselves, which means something must happen to allow these to become heavy enough fall to the earth.

What you need to understand is that the saturation vapor pressure for the pressure at which the air is saturated with water is different when that water is solid compared to when the water is liquid. To be fair, it isn't very much different. Figure 19 shows you the slight difference.

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Figure 19.

The effect of this difference in saturation vapor pressure between ice and liquid water means that at these cold temperatures between zero degrees and -40 degrees Celsius the tendency is for water to escape in liquid form and deposit on ice crystals. This is called the ice phase process, which means that ice crystals will grow bigger even as supersaturated water droplets will get smaller. As you can see, this allows the formation of larger particles of ice or snow in the cloud.

What happens then is that the cloud filled with supercooled liquid droplets provide a ready source for rapidly growing ice crystals. As these ice crystals become larger, they gain mass so they are more likely to fall. Just as is true for liquid water, updrafts in the clouds will cause larger ice particles to grow. Ice crystals can collide with supercooled water droplets, causing these droplets to freeze onto the ice crystal. This is called riming or accretion. The clump that is formed is called a graupel, which is a snow pellet. In

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colder clouds, ice crystals can bump into one another, destabilizing them so they break into even smaller pieces. These smaller pieces act as seeds to make more ice crystals.

Through the process of aggregation, ice crystals collide and clump together to form what we now know is a snowflake. You need at least 100,000 times to 1 million times more water droplets in a cloud than ice crystals in order to get snow.

TYPES OF PRECIPITATION Let's look at the different types of precipitation you might see: •

Rain – as you know, being can be 0.02 inches or more in diameter. You can have smaller droplets of rain then this if they are widely separated; otherwise it would be called drizzle.

•

Drizzle – these are very fine drops of rain that are fairly close together and seemed to float in the air as they fall gently to the ground. The drops are of uniform shape and size and, if any smaller, might be suspended in the air as you see in fog.

•

Ice pellets or sleet – these are small transparent ice pellets which are fairly round and hard to the touch. You can think of them as small grains of ice or frozen raindrops. It is also possible for them to be snowflakes that melted and then refroze.

•

Hail – you know these as balls or clumps of ice that are at least 5 millimeters or one fourth inch in diameter. Should hail become greater than one inch in diameter, this is relatively severe and can cause a lot of damage on the earth's surface. These large hail clumps are seen with severe thunderstorms. The largest documented hail stone was found in South Dakota to be 8 inches in diameter.

•

Snow pellets – these are also called small hail. By definition, the diameter is less than 5 millimeters or less than one fourth inch. They tend to be much more opaque than hail and can be of varying shapes, although they are usually spherical.

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•

Snow – snow is of course snow crystals that have the typical hexagonal shape in the form of a 6 pointed star. This shape is because it is the shape of microscopic ice crystals that then grow to be a crystal of snow you see as a snowflake.

•

Snow grains – this is essentially frozen drizzle. These are extremely small grains of ice that are white or opaque. They are smaller than ice pellets with a size that is approximately one millimeter in diameter or less.

•

Ice crystals – these tend to be seen only in extremely cold regions around the earth. Another name for them is diamond dust. They can be shaped like columns, plates, or even needles. They are so fine that looks like fog, except that these will fall to the ground. There is an optical illusion they create called an ice pillar, which comes from artificial light on the ground as shown in figure 20:

Figure 20.

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•

Freezing rain – this involves supercooled rain that falls to the ground, is exposed to the cold ground surface, and freezes. As you know, this is quite dangerous if you're traveling on the road when this happens.

•

Sleet – you commonly see sleet when the temperatures are near freezing. Sleet is defined as a mixture of snow and rain that can be caused by partial melting of flakes as they fall.

MEASURING PRECIPITATION The branch of meteorology associated with measuring precipitation is called watershed hydrology. The goal of these researchers is to find the best ways to measure precipitation so that it is accurate.

With respect to rain, it is often measured with a rain gauge. Most rain gauges have some type of funnel that drops water into some collection chamber. The amount of water in this chamber is measured automatically or periodically and then recorded. You need to know the size of the funnel and the size of the collection chamber to know exactly how much rainfall the rain gauge is recording.

The standard rain gauge or SRG is not your typical small glass tube you put outside your backyard. It is a large metal cylinder with a funnel to gather rain. There is a measuring tool in the middle that can take up a total of 2 inches of rain. Beyond that it must dump the rain into a larger outer cylinder. Figure 21 shows you this rain gauge:

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Figure 21.

In the wintertime, the funnel and the small inner tube are removed so that snow can collect in the metal outer tube. The snow must be melted in order to get an accurate water equivalent. The downside of this type of rain gauge is that it must be attended to at all times.

Certainly, a rain gauge that can record precipitation over a period of time and documented would be preferable. Rain gauges that do this are called recording rain gauges. They record all precipitation collected during a 15 minute period of time, weigh it, and determine what depth that weight of water would be. A punch tape records the depth. This must be attended to once a month, where the punch tape is collected and changed out each month. There are specialized ones that are heated in order to measure the amount of snow and ice in a bucket that can then tip out and start over. These tipping bucket rain gauges can record the amount of rain in a variable amount of time, because it logs rainfall or snowfall every time the bucket tips. The downside of these is that they can under determine the amount of precipitation if it is raining quite hard.

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In addition to these types of rain gauges, you can get optical sensors as well as impact sensors that can measure the size and total number of drops that strike the surface.

Larger drops contain more water, which is used to calculate the total depth of the rainfall. Doppler radar sensors can detect how fast a raindrop is falling to the earth.

None of these sensors actually collect the rain that falls on them.

Your rain gauge funnel should be one meter off the ground and should have its opening level and horizontal. Needs to be away from any tall objects, but it should also be away from widely open areas; this is because wide open areas prone to wind, which will affect rain deposition. An open space in a grove of trees would be perfect.

Rain gauges are not perfect. The word undercatch refers to the amount of rain caught compared to the actual rain that fell. Most of the undercatch occurs because of the effect of wind, but some of it occurs because of raindrops sticking to the inside of the rain gauge. This is due to the surface tension of water. Under catching because of raindrops sticking to the rain gauge is more prevalent in light rains with only a little bit of rain collection. This is why the people who make rain gauges try to use substances that water doesn't stick to very well. There are comprehensive calculations that can help determine how much the undercatch is.

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KEY POINTS FROM THIS CHAPTER •

Atmospheric stability is a complex term that tells you what will happen in the atmosphere depending on the humidity level and warmth of any given air parcel.

•

Precipitation starts in clouds with various types of nuclei that are hygroscopic, attract water molecules, and allow them to grow to various mechanisms.

•

The cloud-based water or ice particles are too light to overcome the friction of air, so they do not fall to earth.

•

When a water particle or ice particle reaches a certain size, it will overcome the friction of the earth and will fall to the ground because of gravity.

•

Precipitation varies greatly from moist rain to various types of ice particles, including supercooled water particles that fall to the earth as freezing rain.

•

Recording precipitation is not easy; however, there are several different types of rain gauges and rain sensing devices that can say a lot about how much rain or other precipitation has occurred as well as other factors, such as the speed of rainfall.

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CHAPTER FIVE: QUESTIONS 1.

When you talk about an adiabatic processes, what aspect of the process remains the same by definition? a. Volume b. Temperature c. Pressure d. Density

2.

If you have warm air parcel and lift it to higher altitudes, what would happen to it? a. It would cool and contract b. It would expand and warm up c. It would condense into clouds d. It would expand and cool

3.

What is the wet adiabatic lapse rate for any air mass that has moisture in degrees Celsius per kilometer in elevation? a. 1.5 b. 3.0 c. 4.5 d. 7.0

4.

What is the altitude called when the bottom of the cloud layer can be seen, above which the air parcel is hundred percent condensed? a. Equilibrium level b. Level of free condensation c. Level of free convection d. Lifting condensation level

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5.

Which type of cloud would you expect to be a mixed phase cloud? a. Cumulonimbus b. Stratocumulus c. Stratus d. Cumulus

6.

By what size factor will a raindrop be compared to the condensation nucleus it came from? a. 5 times bigger b. 10,000 times bigger c. 100 times bigger d. 700 times bigger

7.

Which type of ice crystallization forms without involving liquid water? a. Immersion freezing b. Contact freezing c. Deposition freezing d. Homogeneous freezing

8.

What is another name for a graupel? a. Snow pellet b. Snowflake c. Hail d. Ice nucleus

9.

Which type of frozen precipitation will you only see in the colder regions of the earth? a. Ice crystals b. Ice pellets c. Snow grains d. Snowflakes

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10.

Which type of precipitation is dangerous to drivers because it results from supercooled liquid raindrops that freeze on contact with the earth? a. Ice pellets b. Freezing rain c. Sleet d. Snow grains

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CHAPTER 6: AIR PRESSURE AND HOW WIND FORMS In this chapter, you will finally study wind and the movement of air from high-pressure to low-pressure. You will learn how wind speed and direction is measured, and how to create isobars on a surface map. With this knowledge, you will understand how to interpret surface maps as well as how meteorologists use these maps in part to predict the weather. After you finish this chapter, you may also be able to predict the weather in your neighborhood based on these maps.

ATMOSPHERIC PRESSURE CHANGES Remember that air pressure varies from place to place on earth, and that it decreases with altitude. Air pressure can be thought of as the weight of a column of air in a specific area. If you are in a high pressure system, this weight will be higher than if you are in a low-pressure system. We will talk about how air pressure changes from place to place in a minute. Meteorologists use several different ways to measure air pressure using barometers. A simple one is the atmosphere measurement, where one atmosphere is defined as the average air pressure at sea level on earth. This is equivalent to 760 millimeters of mercury or 760 torr.

If the air pressure was the same at all levels throughout the planet, we would have no wind and significantly less weather. As you probably already know, there are highpressure systems and low-pressure systems everywhere on earth. If you measure the air pressure in millibars, the average on earth would be 972 to 1050 millibars. The highest known air pressure was detected in Siberia and was 1084 millibars. The lowest reported air pressure was just 870 millibars, which was detected in the eye of a storm near Guam in 1979.

Low-pressure systems are also called depressions; these are called depressions because their air pressure is less than any surrounding air pressure. You probably know that low-pressure systems usually mean the air is warm, the winds are relatively high in the

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atmosphere is lifting. Many low-pressure systems are associated with bad or turbulent weather. The temperature in low-pressure systems does not change very much because of cloud cover that prevents loss of heat during the night. These same clouds trapped air that is warm beneath them.

High-pressure systems are sometimes known as anti-cyclones. Again, you define a high pressure system simply because the pressure is higher. Remember this fact: high pressure systems move clockwise when in the northern hemisphere and counterclockwise when in the southern hemisphere. This fits with the common knowledge that weather usually comes from the West in the northern hemisphere.

There is a phenomenon you should know about called subsidence, which means that this high-pressure air cools down becomes denser than normal and falls for the ground.

The downside of that is that it causes evaporation of the atmosphere in that area. Think about it. If the air is depleted of water vapor through evaporation, it means the weather will be clear and dry. Without clouds, there is a larger difference between the daytime and nighttime temperatures.

There are different atmospheric regions known on this earth to be relatively stable and consistent over time. The stability helps meteorologists predict the weather patterns in this area as well as weather coming from this area. Let's look at the different atmospheric regions: •

The equatorial low-pressure trough – as you can imagine, this is an area around the equator + or -10 degrees from this line. Most of the air is ascending in the atmosphere, is relatively light, and of course it is warm. This is a region of what is called converging air. What this means is that there is horizontal movement of air from outside this region. The air is warm and wet, rises easily because of its energy level, creating clouds. This convergence of wet air these to a great deal of rainfall in this area.

•

Subtropical high-pressure air – these are also called high-pressure cells; you can find them at about 30 degrees above or below the equator. The air is very hot and dry, because a great deal of the water vapor in the stair evaporates. In addition,

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any humidity in this area is removed by the heavy rain closer to the equator. The winds in this area are called westerlies.

•

Subpolar low-pressure cells – these are much further away from equator located at about 60 degrees above and below this line. The air tends to be wetter than normal and relatively cool. This is because there are cold masses closer to the North Pole and South Pole and warm masses below it, towards the equator these converge in this area, forming the polar front and a low-pressure system. This type of low-pressure cell is why we have the precipitation we do in the Pacific Northwest in many parts of Europe. In Antarctica, is the cells that produce all of the severe weather you see in this region.

•

Polar high-pressure cells – these are of course in the polar region about 90 degrees north or south of the equator. The air is very cold with winds moving from the poles, where the pressure is high, to lower latitudes. The wind here is often called the polar easterlies. Because of the coldness of the air, these winds tend not to be very strong.

What factors can you think of that might affect the air pressure? Let's look at the list: •

Height from sea level – as you know, altitude affects the air pressure so this one is easy. As you go up in elevation, the air pressure will drop simply because the column of air between the earth and outer space is not as deep.

•

Temperature – as you already know, air expands when it heats because of the kinetic energy in the air molecules. This expansion reduces the density of the air and also causes a low-pressure area. Cooler temperatures shrink an air mass and increase the pressure. A common quote in meteorology is that, if the mercury in a thermometer is rising, the mercury in a barometer will be falling.

•

Humidity – humidity means there are lots of water vapor molecules in the air.

These are relatively lightweight molecules that rise away from the earth. What this means is that the air pressure of humid air will be less than the air pressure of dry air. As humidity levels change in your region, so will the air pressure.

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•

The effects of gravity – gravity is what helps the atmosphere stick to the earth in the first place. Intensity of gravity is highest in the center of the earth. You need to realize that the Earth's rotation causes a relative flattening of the spherical Earth so that the distance between the north pole, South Pole and the core of the earth is less than the same distance at the equator. In essence, the earth is squished so that there will be higher pressures in the poles compared to the equator.

•

Earth's rotation – anything that rotates will have a centrifugal force. The earth is no exception. The effect of this centrifugal force is greater at the equator essentially pushing the atmosphere away from the earth, decreasing its density so the air pressure is less.

When you know that the barometric pressure is decreasing, it helps to figure out why it is happening. As you study forecasting, you will realize that the barometric pressure you read in a barometer may not necessarily reflect how you forecast the weather. The atmosphere is more complex than you think with a lot of processes going on at the same time; this is likely why meteorologists can only make an educated guess as to what kind of weather is expected at any given location.

While we know a lot more about the weather and barometric pressure and we did in the 1800s, an Englishman in 1848, made these observations both the weather and barometric pressure that are still true today. These were his observations: When the barometer is falling: •

There will be thunderstorms if the weather is hot

•

Frost will thaw if it is colder

•

It could be wet After the Barometer Falls

•

If the weather is fair and the barometer consistently falls, it will be wet and windy

When the barometer is rising: •

If it is winter and the barometer rises, there will be frost

•

If it is already frosty, a rise in the barometric pressure means it will snow.

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•

If the weather is fair after the barometer rises, it will not last.

•

It is wet and there is a sudden rise in the barometric pressure, it will not be nice for very long outside.

•

In England (where these rules took place) the barometer will rise the most for north and east winds.

If the barometer is unsettled or unsteady: •

If the barometer is unsteady, you can expect unsettled weather.

•

If the barometer says it is rainy and rises to the middle, you can expect a short period of good weather.

•

If the barometer says good weather and it falls to say changing weather, you can expect bad weather.

So, in most cases a rising or high barometric pressure means the weather will be without precipitation, while a low barometric pressure indicates rain.

WIND FLOW Let's try to put together a better picture of air movement around the earth. You know that warm air rises, so it makes sense that when it does this you will see a low-pressure system on the ground. The air has risen so the pressure near the ground decreases. Like any system of gases, a low-pressure system is ripe for the movement of air around it to be sucked into the low-pressure. This horizontal movement of air is called advection.

On the other hand, cool air will fall creating a high pressure zone near the ground. Air in the atmosphere will always flow from an area of high pressure to low-pressure. If you think about it on a molecular basis, it makes sense. High pressure areas mean lots of molecules or molecules with higher kinetic energy; these will naturally travel to low pressure areas with fewer molecules at a lower kinetic energy. Figure 22 shows you how complex it can get when you consider that air masses are moving all over our globe:

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Figure 22.

Around the earth, the whole thing becomes a series of circles. In any given area, you will see a circle of low-pressure with warmer air rising upward, cooling, and then sinking downward. There will be horizontal flow at all times from areas of high pressure to lowpressure. Anytime you see wind, it will be because of advection.

Convection is something you already know about. It helps to create weather too by allowing temperatures to rise and fall according to their warmth and other things, like the amount of water vapor they have in them. Warm air that ascends with humidity can no longer hold this humidity as it cools, so clouds form and it rains or snows. Cooler air falls and warms up as it reaches the earth. It can now hold a lot more moisture without raining and the warmth allows the air to accept evaporated water from the ground. You can see now how the whole thing is one big cycle. Around the globe, there are global wind belts where air is continually moving, affecting the climate in the region on a yearly basis. Within these regions are smaller air pressure systems that create local weather.

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You can also see that the wind you experience in your neighborhood is basically advection at work. There is continually moving air from areas of high-pressure to lowpressure. In a large high-pressure system, the air will hold back winds and you will see light winds and fair weather. In some low pressure systems, you will see wind because the air is moving into it. Let's look at some specific local wind patterns.

Have you ever heard of sea breezes? In any large body of water, the air is more humid and on land. Humid air holds onto its heat so it doesn't change as much over time. If there is any large temperature difference between the air on land and the air at sea, you will see a difference in the pressure of air between the two places. This is what creates breezes.

A sea breeze happens when the air is warm over land and cool over the ocean. This will happen mainly in the summertime. The cool air from the ocean then flows as a gentle breeze on to the land and about 10 to 20 kilometers per hour. Land breezes are seen in the wintertime when the air cools more over land that it does over the water. In this case, the breeze will come from the land out to the ocean. It can also be seen when air cools differentially in the daytime versus the nighttime, as seen in figure 23.

Land breezes are seen at night and sea breezes are seen in the daytime.

These local breezes are moderating to the area of land near the oceans or large bodies of water. You see this in areas like Southern California, with the breezes moderating the air up to 60 miles away from the shoreline.

Monsoon winds are much bigger than the land and sea breezes, but they are based on the same phenomenon. You see them on hot summer days from sea to the land or in the opposite direction in the wintertime. These are so strong that you will see thunderstorms and monsoon rains. You see them all the time in India; they contribute to the monsoon rains most people in the area depend on for crops and drinking water.

They used to help sailors get back home from Africa or go there when goods were trafficked between India and Africa.

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Figure 23.

You also can have valley and mountain breezes. Daytime means the air overheats on the slopes than in the valleys, drawing cool air up into the mountains, causing a valley breeze. At nighttime, the reverse happens and you get a mountain breeze that flows

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downhill. Katabatic winds are these same breezes on steroids, forming over high plateaus, where the air gets cold in the wintertime. This cold air sinks downward, causing large winds coming off of these high plateaus. In Greenland and Antarctica, these winds are both strong and cold.

Chinook winds are related to mountain ranges. Air is forced upward up and finally over a mountain range. Westerlies from the Pacific push these winds over the Sierra Nevada Mountains. This air is naturally warm and moist. Once over the mountain range, this air cools and, because of this, it cannot hold that moisture anymore. It may rain or snow; it also forms high pressure on the leeward side of the mountain. This is the side opposite where the wind is coming from. The air drops down, forming hot and dry winds on the lands near this leeward side. Chinook winds cause rapid temperature increases, melting snow on the leeward side, and what's called the "rain shadow effect", which is the formation of deserts brought on by hot dry winds. All of the precipitation has been left behind on the mountain tops.

Santa Ana winds are seen during the late fall and winter months in the same area of California. East of the Sierra Nevada, the atmosphere cools. Cooling means that a high pressure system is created. Winds travel downhill and always in a clockwise direction.

The temperature rises and there is less humidity in the air mass, creating large wind flow in the southwest from the land to the ocean. These hot and dry winds make the California landscape even drier, which is why they lead to large-scale fires in Southern California.

You often associate winds with cold days and bad weather but, in reality, winds can be hot as well. You see this with the Santa Ana winds. You can get similar winds in any desert; these can be linked to great monsoon storms. Remember that deserts have mostly sand or dirt but little vegetation. The winds pick up these particles. You will get what's called a haboob, which is a severe dust storm at the beginning of these wind fronts. Whirlwinds of dust form in these areas as hot air rises, creating pockets of low pressure that spin. They do not last long but can be damaging. The dust also provides fodder for monsoon storms over any nearby ocean. Figure 24 shows what a haboob looks like:

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Figure 24.

HOW AIR MOVES IN THE ATMOSPHERE AROUND THE GLOBE There are predictable ways that the atmosphere travels around the globe. Remember that the sun is stronger near the equator, so warm low pressure systems form. Near the top of the troposphere, some of the air moves northward while the other half moves southward. Of course, this air cools as it travels. Eventually sinks back down and gets sucked back toward the equator. You can see now that a circulatory pattern is set up.

This circulatory pattern is a convection cell.

Remember also that the earth rotates. This complicates the convection cell, so that the cooled air lands further to the right than it should. This is only because the earth has rotated. This leads to what we call the Coriolis effect. Figure 25 shows how this works:

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Figure 25.

In the northern hemisphere, the air coming from the equator meets the air coming back to the equator at about thirty degrees north latitude. Both of these batches of air descend, but for different reasons. Where this air mass descends, you have a high pressure area. You now know this as the subtropical high pressure zone. There is a tiny convection cell caused by this effect. It is called the Hadley cell, located between the equator and thirty degrees north latitude. Figure 26 shows all of these cells around the globe; it explains many of our typical wind and weather patterns:

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Figure 26.

There are other convection cells in the Northern Hemisphere. It is the Ferrell cell between thirty and fifty degrees north latitude. Above that is the Polar cell between fifty degrees latitude and on up to the North Pole. In the southern hemisphere, the Coriolis effect makes objects such as air masses at the left, giving three mirror image circulation cells, for a total of six major convection cells on our globe.

Because of these convections cells and the earth's rotation, you now have global wind belts. These are stable wind patterns moving horizontally from high to low pressure.

These are called the Northeast trade winds going in the southeast direction and linked to the Hadley cell, the westerlies in the higher latitudes going from west to northeast above 30 degrees north and linked to the Ferrell cell, and the polar easterlies from northeast to southwest. In the southern hemisphere, you now have the southeasterly trade winds below the equator heading in the northwest direction, the westerlies to the south going from northwest to southeast, and the polar easterlies.

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The polar front is created by the boundary between the Ferrell cell and the Polar cell.

Moist air from the equator mixes with high-pressure cold air. The end result is a potential for unsteady air in North America and much of Europe. The polar jet stream is very high and is where the cells meet. The temperature difference is large here so the wind is fast. You probably know that it's the jet stream that aircraft use to conserve fuel in some cases. This stream travels southward in the wintertime and northward during the summer months.

Between the Hadley cell and the Ferrell cell is the subtropical jet stream, which is less powerful than the polar jet stream, but it is based on the same principle. The air is warmer in both of these cells so the temperature variation is less.

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ISOBARIC MAPS

Figure 27.

We will soon look at some weather maps to see how the weather is predicted using these surface maps of our atmosphere. Before we do this, you need to learn what an isobar and isotherms are. An isobar is a line where you can follow on the map to see areas of the same pressure. You will see many lines, reflecting different pressures. An isotherm is the same thing except that is related to areas with the same temperature. Figure 27 shows you a storm pattern over the ocean with isobars reflecting the different air pressures.

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When you look at isobars and isotherms, it will be easy for you now to see where there are low-pressure systems. In the figure you just saw, low-pressure system was obvious as the area in the center of isobars that decreased in air pressure as you moved toward the center. In fact, whether maps often show two letters indicating high-pressure or lowpressure. If you see the H, is a high pressure air mass. If you see the letter L, it is a lowpressure air mass. Any elongated sections of low-pressure are known as troughs. Any elongated section of high-pressure is known as a rich When you study isotherms on a map, you can often predict where the wind is blowing. If a series of isotherms are very close together, there is a large temperature difference over a short space on the map. Of course, this will be an area where wind will travel across a shorter temperature gradient. The same is true for isobars; if these are close together, winds will be high. We will study surface maps in a minute. You can see however, that these isobars and isotherms provide a good pictorial representation of a lot of the data collected in different parts of the world.

SURFACE AND UPPER AIR CHARTS Now we can study real weather maps. While these are interesting, the real goal of them is to predict what type of weather you can expect in the next hours, days, or perhaps a week or more in length. Meteorologists often show these maps on the news; now you will be able to read them too.

What you can now imagine is that people collect information about the current temperature and pressure in their area. This data is put together to create isobars and isotherms. In addition, we have radar to show there are current storms in areas of precipitation. All of this information is put together to make predictions. Many of these weather maps are color-coded so you can see that red areas indicate warmer temperatures while green and blue areas on the map indicate cooler temperatures.

You've probably heard of cold fronts and warm fronts. A front is the edge of any moving air mass. Symbols on the surface map will tell you not only if it is a cold front or a warm front, they will tell you the direction the air mass happens to be moving. A stationary front will also be marked in a way that makes it easy to see that the front is not moving.

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Figure 28 shows you clearly what the symbols mean on the surface map. Warm fronts are labeled red with half circles on the line with the front is coming. Cold fronts of blue triangles marked at the edge of the cold front. Stationary fronts have both types of symbols on them. Cold fronts often mean bad weather and storms, while warm fronts often mean that warm and sunny weather is coming.

Figure 28.

Often, you can look briefly at the surface map and be able to say where there is precipitation expected. Precipitation most likely comes when the front is advancing; the precipitation is seen at the edge of the front as it enters a certain area. You might also see special symbols on the map indicating thunderstorms, rain prediction, or coming snowfall. In the northern hemisphere, many fronts operate from a westerly direction to an easterly direction, although you will see some North or southward tendency. Figure 29 demonstrates a simple map of the United States with warm and cold fronts easily depicted:

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Figure 29.

By looking at the weather map and because you now understand the flow of air, you can predict the direction of airflow. In the northern hemisphere, a low-pressure system will rotate in a counterclockwise direction. In reality, you need to remember that because of the Coriolis effect, it will flow in a rightward or easterly direction; because of the low pressure in the center, this will cause a spin in the counterclockwise direction as shown in figure 30: High-pressure systems always rotate clockwise, because the air is expanding outward and not moving inward as you would see in a low-pressure system. This is only true in the northern hemisphere. The rotation of high-pressure and low-pressure systems will be the reverse in the southern hemisphere. You will need to look at isobars to predict just how fast the wind is blowing and in what direction. While there are upper-level maps and surface level maps, your weather is mostly determined by surface level maps, which indicate where the air is flowing near the ground.

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Figure 30.

TYPES OF WIND INSTRUMENTS In order to get the information you need for a weather map, you will need many people to collect the data on the ground. One piece of data that is collected is the wind speed and direction. As you can imagine, these things are important when it comes to predicting the weather and what to expect.

The most basic tool for measuring wind speed and direction is the anemometer. A weathervane is a simple example of this. These devices have cups on the ends of blades that catch the wind and spin. Certainly, if the wind is blowing rapidly, the propellers will spin more swiftly. When these are calibrated, you could actually predict the wind speed.

Meteorologists often use hot wire anemometers, which are very capable of detecting small changes in the wind. Essentially, they use wind power to heat a small wire. A hotter wire means more wind speed. Figure 31 is a simple anemometer: 57

Figure 31.

As of the 1960s, we can now use Doppler radar to measure wind speed and the direction of the wind during storms. You can imagine how much more accurate these can be and how they are able to detect very specific things within a storm in order to protect people on the ground. These devices use radar, which essentially tell the flow of air anywhere the radar is projected toward. The waves set into the storm are deflected back to the device. Depending on the wind speed and direction, the waves deflected back and detected by the device will vary in wavelength. The device then color codes the information it receives and displays it on a nice map for you see the wind speed. Genius, isn't it?

You can also use laser-based radar called LIDAR and sound based radar called SODAR to detect wind; these are often used in calibrating things like wind turbines and not for weather determination.

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MEASURING WIND DIRECTION AND WIND SPEED As mentioned, you should be able to predict both the wind speed and direction. When you report wind direction, you need to report the direction the wind is coming from. If you say there is northerly wind, for example, you need to say the wind is coming from the north and that it is going to the south. You can also use one of the cardinal directions (north, south, east, or west) and then give an angle. This will be different from your typical angles you write on paper. When you report wind direction as coming from the north, you will report that as zero degrees. Wind coming from the east to the west has an angle of ninety degrees. Wind coming from the south to the north has an angle of one hundred eighty degrees. You get the idea.

People also want to know the wind speed, so you will say that the wind is coming from the east at twenty miles per hour or perhaps fifteen kilometers per hour, depending on where you live. This way, people know to expect where the coming from and how strong it will be.

If you happen to use a windsock or a weathervane, you can still get the wind direction. A windsock has an opening that will face where the wind is coming from the tail that faces where the wind is going to. A weathervane also points in the direction the wind is coming from. This doesn't make a lot of sense, because you would think the arrow would tell you where the wind is going to. Just remember that is actually pointing toward where the wind is coming from. Obviously, you can also use your index finger after you wet it. The pad of your finger will feel the coolest if it is pointed toward where the wind is coming from.

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KEY POINTS FROM THIS CHAPTER •

Air masses flow through convection in a vertical direction up or down. Warm air is not very dense, so it rises and cold air is dense, so it falls

•

If the earth did not rotate, they would only be flow of air from the poles to the equator and back again. Because of the Coriolis effect, you have six different convection belts around the earth.

•

Because of the Coriolis effect, air masses will be deflected to the right or eastward in the northern hemisphere and to the left or westward in the southern hemisphere.

•

There are predictable patterns of weather on earth based on the movement of air masses. There is a polar jet stream and a subtropical jet stream, formed where two stable air masses meet one another.

•

Isobars and isotherms are used to tell you areas of equal temperature and equal pressure on a weather map. You can predict where low or high pressure systems are located based on the isobars.

•

You should familiarize yourself with the different symbols you see on a weather map or surface map.

•

Wind speed and direction can be detected in several ways; however, an anemometer is usually sufficient unless you have a Doppler radar system to detect wind speed and direction in severe weather systems.

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CHAPTER SIX: QUESTIONS 1.

What conditions will you least likely see in a high pressure system? a. Clear skies b. Dry air c. Windy conditions d. Large variations in diurnal temperatures

2.

What stable air system is most responsible for the precipitation received in the Pacific Northwest? a. Equatorial low-pressure trough b. Sub polar low-pressure cells c. Subtropical high-pressure air d. Polar high-pressure cells

3.

Which situation does not promote a sea breeze? a. The wintertime months b. A large body of seawater or ocean c. Warmer air over land d. High humidity over the ocean

4.

Which of these two conditions is most conducive to having a land breeze? a. Winter and nighttime b. Winter and daytime c. Summer and nighttime d. Summer and daytime

5.

What would you find in the atmosphere near or in a haboob? a. Ice crystals b. Rain droplets c. Sand particles d. Still air

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6.

Which upper level winds dominate the area above the United States? a. Westerlies b. Northeast trade winds c. Equatorial doldrums d. Polar easterlies

7.

Which statement is true in the Northern Hemisphere about air cell spinning? a. High-pressure systems and low-pressure systems both spin clockwise b. High-pressure systems spin clockwise and low-pressure systems spin counterclockwise c. Low-pressure systems spin clockwise and high-pressure systems spin counterclockwise d. Both low and high pressure systems spin counterclockwise

8.

You see a weather map with a line showing red half-circles and blue triangles about 200 miles to the east of you. How would you interpret that line? a. A warm front and good weather is ahead b. A cold front and good weather is ahead c. A stationary front exists so it would be hard to predict the weather. d. A cold front has just come through your area

9.

You are a new meteorologist to your vicinity and you want to be able to tell people when to take cover during a storm because of high winds. What device will you buy? a. Several anemometers placed strategically in your area b. A new visual satellite system c. A new Doppler radar system d. Several barometers placed strategically in your area

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10.

You are reporting the wind direction and say that the wind is coming at an angle of ninety degrees. From which direction on land do you expect the wind to be coming from? a. North b. East c. South d. West

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CHAPTER 7: CIRCULATION IN THE ATMOSPHERE In this chapter, we dive deeper into the complex circulatory patterns seen in the atmosphere. There are the global patterns discussed earlier and many others that affect local weather conditions all over the world. The oceans and large lakes exert their own effect on the earth's weather systems beyond what we've already discussed, which will be covered in this chapter. By the time you finish the chapter, you should be able to demonstrate how and why the atmosphere behaves as it does.

GENERAL CIRCULATION The term general circulation is the term used to describe Global wind patterns. We've already talked about many of these. The reason we have general circulation is because of differential heating around the earth. As you know, differential heating is the driver for changes in air density. Air will naturally go from an area where it is more dense to an area where it is less dense. Each of the phenomena associated with this provide reasons why we have prevailing winds. Prevailing winds are basically a general term to describe the general direction of wind flow. In the United States, it is westerly or from west to east, except in Hawaii, where it is a north easterly wind.

You already know that differential heating mainly comes from the fact that solar radiation is much stronger at the equator than it is at the poles. The reason for this is because the earth is a sphere with the generally facing the sun. As the sun reaches us, rays of light must fit in a smaller surface area, however, the surface area for the same intensity of light is much greater at the poles. As the surface area increases, the density of light rays is decreased.

You need to remember that the amount of heat on earth at any given point in time is equal to incoming radiation minus outgoing infrared waves from the earth itself.

Emission of these waves is happening all the time—day and night. This Infrared radiation is dependent on the temperature of earth itself. The average input and output

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is the same but only when you do an average across the earth. Because input is less at the poles, the net heat there is a loss of heat. The opposite is true at the equator. It's because of this differential that general circulation occurs.

You can imagine all of this heat surplus at the poles spreading upward and downward toward each pole, where there is a heat deficit. Because the earth is spherical, the greatest deficit is not at the poles but at around 60 degrees latitude. You get this general circulation then, which is the earth's attempt to redistribute heat from high heat to low heat areas. Because this isn't an instant process, you will have obvious changes across the globe.

You already know that there is not a single cell from the poles to the earth. You would have to assume that there were no land masses on earth, that no seasons existed, and that the earth was not turning. This would mean that the Coriolis effect was not present.

We would only have the Hadley cell, which would be one giant convection belt from the equator to the poles and back again. Surface air in the northern hemisphere would always head southward.

So, if temperature was the only factor, you would see low-pressure at the equator and high-pressure at the poles. You know this is true because warmer air has a lower pressure associated with it. It is also true that warm air rises, so the warm air at the equator rises and then is shifted toward the poles as an upper level air mass. Together these factors account for the convection belt you would see.

You also know that because of the Coriolis effect, we have three cells per hemisphere: the Hadley cell, the Ferrell cell, and the Polar cell. What we didn't talk about yet was what happens at the Polar cell because the most heat deficit on earth is at the bottom of the cell and not at the poles. Because of this, there is a relatively steady cold front pushing air downward from the poles. Above each pole is what you call a polar high.

Around the equator, the boundary between the two Hadley cells (North and South) is called the doldrums. Between the Ferrell cell and the Hadley cell is an area we call the horse latitudes.

In the doldrums, the weather is exactly what you would expect. It is monotonous and warm with rising humid air and frequent rains or thunderstorms. All rising air stops at

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the tropopause. The massive clouds and rain in this area give off even more heat because of condensation, which heats up the area even further. Near the tropopause, the air has no place to go except northward.

The subtropical high region at approximately thirty degrees latitude is also called the horse latitudes. This area experiences little rain and usually has sunny skies. Over the ocean the winds are light with north easterly winds in the northern hemisphere or south easterly winds in the southern hemisphere. These are exactly where the trade winds are located. In the United States, only Hawaii largely affected by this area. The inter-tropical convergence zone is where the trade winds from the north and south come together.

The polar front exists partly because the two air masses between the polar and Ferrell air cells do not mix very well. There is a low-pressure system in that area called the subpolar low. As you already know, low-pressure systems usually mean storms. This means that between approximately 50 to 60 degrees latitude, you can expect this front and the increase in storms. Below this area, you get the Ferrell cell, in which you can also expect cool air to rise and warm air to sink. This is called thermally indirect circulation.

You should know that there are some areas of the world where it seems to be a high pressure system most of the time. These are called semipermanent highs. You also see some areas called semipermanent lows. The two major high areas are the Bermuda Azores high as well as the Pacific high. The two low areas are the Aleutian low and the Icelandic low. The Pacific high is also known as the Hawaiian high. There are also areas near Tibet and just above the Antarctica continent where there is low-pressure or troughs. The equator is also where you would say that a trough existed.

Remember the jet streams? There are two of them and they are not the same. The subtropical jet stream at thirty degrees latitude lies about thirteen kilometers high in the sky. The polar jet stream at approximately sixty degrees latitude is only about ten kilometers high. This is because the tropopause is higher near the equator. The air being dense more toward the poles squishes down the polar air so the jet stream is not as high in the sky. As you know, the jet streams involve very strong wind going roughly from

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west to east. In the middle of the jet stream, you'll see the jet streak where wind speeds are as high as two hundred knots.

LOCAL WIND SYSTEMS We have already talked about many local wind systems, such as sea breezes, land breezes and katabatic breezes. Most of these have a diurnal pattern passing just a few hours a day and many affect a small area on the earth's surface. We have not, however, talked about all of these kinds of local wind systems. Let's review them: •

Anabatic winds – these come from slopes that are heated by the sun, expanding the air upward. Cool air is down below in the valleys. This causes a slight breeze up a slope. These of course happened in the daytime.

•

Katabatic winds – these are downslope winds that occur when the air on the slopes cools. This air becomes dense and slides down the slopes, leading to nighttime winds that head down the mountainside. Neither of these winds is very strong, usually only 3 to 4 meters per second.

•

Sea breezes – these are cool winds that come in from the sea after the lowpressure system develops just inland over warmer air. This brings in cool and moist air from the ocean. The speed of these breezes depends on the temperature differential exerted by the sun and other forces. These breezes occur during the daytime.

•

Land breezes – these of course come from the land and spread out to the sea, occurring mainly at nighttime or in the early morning hours before the sun warms. They occur at night because the air cools more over land that it does over the sea.

There are many of these breezes that are named according to the region. Here are some examples: •

The Bise – this is seen in the mountains of France and Switzerland in the wintertime.

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•

The Bora – this is a strong and cold wind located in the mountains along the coastline of Croatia.

•

The Foehn - these are warm and dry winds seen on the lee side of mountaintops.

They can be very strong and can occur suddenly. These are the same thing as Chinook winds except they are located elsewhere, such as in New Zealand or in the Alps.

•

The Khamsin winds – these are dusty winds seen in Egypt in the springtime.

•

The mistral winds – these are extremely strong winds in the Rhône Valley of southern France, usually seen in the wintertime.

You do not need to memorize all of these winds unless they exist in your area. You can expect them to occur at various times of the year and cause a varying degree of damage to property.

AIR POCKETS AND EDDIES If you've ever traveled by air, you know about air pockets. These can be scary times for airline travelers and represent situations where to bodies of air moving and greatly different speeds and meet together. Airline pilots and meteorologists call this CAT, which stands for clear air turbulence. What this means is that you cannot see anything in the air itself to let you know is coming.

Air pockets tend to be seen at about 7000 to 12,000 meters above the earth's surface and upper troposphere area. You might also see them at the tops of certain mountain ranges. If you see cirrus clouds, it could indicate a higher probability of having an air pocket. Most air pockets are just uncomfortable, but a few can be dangerous.

It is very difficult to detect where an actual air pocket is located, even if you have conventional radar equipment. The best ways to detect these are remotely, using a scintillometer, Doppler radar, laser-based radar, and what is called an N slit inferometer. These techniques will all measure turbulence.

There are certain areas where you can predict a higher chance of having an air pocket.

These include near the jet streams, especially if there is horizontal wind shear in the 68

area. Anytime there is a large temperature gradient between two air masses, you may also see air pockets. Remember that you can have vertical temperature gradients as well as horizontal temperature gradients in the upper atmosphere.

What is wind shear? Windshear is when there is a strong difference in the speed of two air masses next to one another. These will produce circular vortices, where the wind is not moving in a predictable direction. Air density and viscosity will change dramatically in a short period of time, leading to areas of slow and rapid air movement that just cannot be predicted.

Another feature associated with air pockets or CAT is a mountain wave. As you can imagine, mountain waves are undulating waves of air that go up the mountain and back down the other side. Air pockets are seen when there are long mountain ranges, strong winds running perpendicular with respect to the mountain range. There should also be a temperature inversion near the top of the range and the maintenance of wind direction across the altitudes. If you meet these requirements, you have a higher wind shear chance.

Wind shear and clear air turbulence can also be affected by gravity wave windshear. This occurs at the tropopause, where the wind beneath it is cold and moves faster. The wind above it is warmer and move slower. You can imagine this rapid change in wind speed could cause turbulence in this area.

It will not affect the weather on earth, but it will affect aircraft travel because airplanes do not work as well when the air density is not consistent or stable. You will see instability and turbulence as an airplane leaves the jet stream, which is unavoidable.

Any changes in course will also affect the chances of being exposed turbulence.

Airplanes also fly at constant altitude to avoid turbulence.

On several occasions, clear air turbulence has been dangerous. There have been situations where passengers have been injured because of this. In nineteen sixty-six a Boeing 707 broke up because of turbulence, with all lives lost on board.

The phenomenon of thermals in the air results from areas of local heating. There will be vertical convection and currents of air caused by this. You will see these usually over areas of sand or bare rock, such as over sand dunes. You can imagine that these are very 69

turbulent areas, however, they usually are fairly close to the ground and do not affect aircraft.

When you see dust devils or dirt devils, this represents swirling air that can extend as high as four thousand feet above the earth, often looking like tornadoes of dust.

Waterspouts over areas of water involve the same phenomenon. Warm air and turbulence sucks water up into the atmosphere, leading to waterspouts.

Dynamic or induced tertiary circulations results in things like eddies in the atmosphere, turbulence, and Foehn winds. Eddies are areas of circulation or turbulence when the wind happens to be flowing over rough terrain, which can include mountains, buildings, or man-made obstructions. An Eddie will form on the lee side of these areas. You can also see eddies in the ocean, found over cold deeper ocean waters. These are actually good for fish near the surface of the ocean. This is because they essentially suck up nutrients from deep inside the ocean and bring them to the surface. The National Ocean service names some of the larger eddies they can see. In the atmosphere, most eddies are set up as circular motion straight winds that suddenly encounter rough terrain of any kind.

LAKE EFFECTS You have probably heard about Lake effect snow. This is common in North America in the Great Lakes region. It happens when there is very cold air below the freezing temperature of water over the warmer lake waters. Some of this Lake water evaporates, leaving behind warmer air that is more saturated with water vapor. As the air cools over land, it dumps this precipitation over the ground. Quite often this means a great deal of wet snow.

Lake effect snow tends to affect weather within twenty-five miles from the shoreline, although you can see dumping of snow as far away as a hundred miles from the shoreline. Places like Buffalo New York are fairly close to a large body of water, so you often see this type of snow entering the wintertime. You will not see it after February, however, largely because the lake has frozen over and it is impossible to steal water from it.

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ATMOSPHERIC OCEAN INTERACTIONS You know that the ocean greatly affects our atmosphere. It's safe to say that the oceans determine much of the weather we experience, even if we do not live near any ocean.

Let's look at how the ocean has such an impact on the weather in all parts of the world.

We will talk a lot more about hurricanes, cyclones, and typhoons. These all originate over the ocean but affect the weather inland. The terms essentially mean the same thing, depending on where they're located on the globe. These are giant rotating air masses with extremely low pressure inside of them. The winds they create are very great, mostly because there is a high differential of pressure from the inside of the air mass to the outside of the air mass.

Hurricanes often begin as low pressure air cells in the Equatorial region. They essentially break off of the low pressure belt located around the equator and travel northward. Because of the Coriolis effect, they will spin in the counterclockwise direction. Like a waterspout but much bigger, they suck water up from the ocean bringing water vapor and a great deal of heat energy into the system. The longer they spend over the warm tropical waters, the more water they collect and the stronger their winds will be. We will talk more about the difference between a tropical storm and hurricane, but of course you know these are the same systems but with different intensities.

SOUTHERN OSCILLATION This section is about what is called the southern oscillation. It actually goes by many different names, such as El Niño and La Niña. Meteorologists call this ENSO, which stands for El Niño Southern oscillation. This is essentially a periodic variation we see in the winds and in the surface temperatures over the Pacific Ocean in the eastern part of the ocean near the tropics. Depending on this irregularity, the weather in the subtropical regions and in the tropics will vary.

You need to understand that when these waters are warm, we call this the El Niño effect, and when these waters are cooler, we call this the La Niña effect. It involves a change in

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both the ocean temperature and the atmospheric temperature and behavior. With El Niño, the surface pressure in the Western Pacific area is high, but with La Niña conditions, this area has low air pressure. Between these two extremes, we say that the effect is neutral. Both of these phenomena last for several months with varying intensities and periodicity that is approximately every few years.

In South America along its western coast, there is the Humboldt current that brings cooler water up from the south toward the tropical regions around the equator. Near Peru, the oceans have an upwelling of water from the deeper areas that contribute to this phenomenon. The trade winds affect this cooling phenomenon as well, by bringing up water from the deeper regions of the ocean to the surface in the Eastern Pacific. This deeper water is also cooler than surface water so it cools the surface water. During an El Niño year, there is less surface water cooling or no cooling at all. The water in the area of the Eastern Pacific is just as warm as the water in the Western Pacific. Figure 32 shows the warmer waters in red in the area near the Panama Canal during an El Nino year:

Figure 32.

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There is the Walker circulation to consider as well. It is a surface water phenomenon that takes water in an east to west direction, where warm air from the sun's rays travels westward toward the Western Pacific area. This sets up a convection circuit whereby surface air that is considered a cool dry high in the east near Peru drops down and becomes warmed by the sun; it then travels along the surface toward Australia where it becomes humidified and even warmer. This air then rises forming clouds and rain in the Pacific Southwest. This risen air then travels along the upper part of the atmosphere back to Peru. It is again a high pressure area and the entire thing start over again. In essence, the Walker cycle occurs because of a pressure gradient between the East and the West Pacific.

Because of the Walker circulation the Pacific Ocean is actually twenty-four inches higher in the western Pacific Ocean. In an El Niño year, the air near Peru is warmer than it should be so that the air in the Pacific near Peru is wetter as well. The entire thing breaks down the Walker cycle.

In summary, the Walker circulation is a pressure gradient that takes cooler and drier air under high pressure in a westerly direction toward areas like Indonesia. This results in a temperature gradient and a humidity gradient above the ocean. Beneath the ocean, there is also a gradient and a flow of water, which results in a change in the depth of the thermocline underneath the water. A thermocline is an area beneath the water with a sharp temperature difference above and below the line.

The reasons for the fluctuations we see in the Walker circulation are complex. There are a number of factors both above and below the equator that can change all the Walker circulation works. When we have an El Niño year, the easterly trade winds are warmer.

The fishermen in Peru and along the coast of Ecuador have good fishing because nutrients are brought up from the depths of the ocean. On the other hand, it creates a situation of warmer and wetter air in the western Pacific. This results in more thunderstorms and typhoons during those years.

We call the phenomena of changing atmospheres throughout the different years the southern oscillation. Is the same thing as El Niño, relates to the atmosphere itself and

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the changes in pressure we see between the Eastern and Western Pacific oceans in different years.

In a La Niña year, the Walker circulation is actually much stronger. This results in cooler temperatures in the eastern Pacific. The impact of a La Niña year is that there is a drop in surface temperature in areas of Southeast Asia. This means there are more heavy rains in areas like the Philippines, Indonesia, and Malaysia. Much further north in Alaska, a La Niña year means drier conditions.

In terms of storm tracks, the storm track will be southerly in an El Niño year. This means more rain in Southern California. The storm track moves more northward in a La Niña year, resulting in more rain in the Pacific Northwest. In the Midwest, a La Niña year means more snow in those areas along with hotter and drier summers. In the Gulf states, El Niño translates to more precipitation. In Hawaii El Niño means there will be a dry season. So, you can see that these southern oscillations can lead to wide differences in the temperature and precipitation from year-to-year in all parts of the Pacific and in the United States itself.

In recent years, meteorologists have recorded far more El Niño events and fewer La Niña events. While there are not enough years to make a decent prediction about this, it is expected this phenomenon will increase further as a result of global warming. In addition to the frequency of the El Niño events, it has also been observed at the amplitude if the variability is also increased. You can expect than that the difference between an El Niño year and a La Niña year will be greater as global warming worsens.

EL NIÑO AND LA NIÑA While it is believed that phenomena like La Niña and El Niño have existed for a very long time, meteorologist not record these until fairly recently. They noted that there was a recurring cycle resulting in weather extremes that fluctuated from dry conditions to very wet conditions in any given area that would be affected by the Pacific Ocean. The Pacific Ocean is one of the main drivers of weather in the United States because weather comes from the West in general. As you can see, weather affects everything from the

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amount of fish gotten in Peru to the number of storms you see in the Gulf states. Figure 33 more clearly shows how a normal year compares to an El Niño year:

Figure 33.

While La Niña years have been present as long as El Niño years, we understand less about them. Because these are also extreme weather conditions, La Niña years and have devastating outcomes in different parts of the world. As you can imagine, the trade winds are very strong and the surface waters near the equator are colder. There is more bad weather in La Niña years, including more tornadoes and other cold weather conditions in the Midwest and in other parts of the world.

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What we have discovered is that there is a cyclical variation from La Niña to neutral and to El Niño again. We know there is a ten year cycle but there are also shorter cycles of 3 to 4 years. Meteorologists have studied the cyclical variations since approximately 1960.

As mentioned, the frequency of El Niño is now greater than is to be and the intensity of El Niño but not La Niña is greater. In the most severe cases, the El Niño effect can be felt throughout the world.

IMPORTANT POINTS IN THIS CHAPTER •

General circulation describes the specific pattern of winds throughout the world.

•

Winds are complex and involve interactions around the earth.

•

Local winds are named according to where they come from. All of them are one of 4 types of winds, including anabatic, katabatic, sea, or land breezes.

•

The term lake effect usually involves being in a location near a large body of water and area where snow is possible.

•

The Southern oscillation essentially means that there are times when the circulation of the atmosphere between of South America and the western Pacific varies.

•

El Niño and La Niña years are warm and cold extremes in temperature in North and South America due to variations in the Walker circulation pattern.

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CHAPTER SEVEN: QUESTIONS 1.

What is the main reason it is hotter at the equator than it is at the poles? a. The earth exhibits a centrifugal force on the equator more than the poles b. The sun's rays have a greater density at the equator c. The equator is much closer to the sun than the poles d. There is more vegetation around the equator than at the poles

2.

What is the net effect of the input of the sun's energy and the output of IR radiation across the entire earth? a. The input and output are equal b. The input is always greater than the output c. The input is always less than the output d. The net effect depends on the length of the solar day

3.

Which two cells around the earth account for the doldrums where they come together? a. Hadley and Ferrell cells b. Farrell and polar cells c. Two Hadley cells d. Polar and Hadley cells

4.

You are sailing across the Atlantic Ocean and want to make the most out of the trade winds in the northern hemisphere. Which direction will you travel if you start out in Spain and set sail? a. North East b. Due south c. Northwest d. Southwest

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5.

Which device will not likely help you detect an air pocket in the skies? a. Doppler radar b. Conventional radar c. Laser-based radar d. Scintillometer

6.

What least likely increases the chance of air pockets when flying? a. Mountains b. Jet stream c. High temperature gradients d. Rain clouds

7.

What is considered not necessary to have lake effect snows? a. A large body of water b. Balmy temperatures c. Cold air blowing over a large lake d. Warmer waters over the lake compared to the air blowing over it

8.

Why do you not see the effect snows late in the wintertime? a. The lake has already frozen over b. The temperatures are beginning to warm c. The air is very dry d. The pattern of wind flow changes late in the wintertime

9.

What can you expect in Peru during an El Niño year? a. Monsoon rains b. Drought c. The cold and dry weather d. More fish to eat

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10.

What will not be seen in an El Niño year? a. Rising in the thermocline along western South America b. Increased rains and monsoon weather in Indonesia c. Weakening or reversal of the Walker circulation d. Warmer weather in the United States

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CHAPTER 8: AIR MASSES, FRONTS, AND MIDDLELATITUDE CYCLONES This chapter will bring you further toward being able to predict the weather. We have talked about things like air cell and convection cycles but not about large air masses that affect our weather patterns. You know about fronts from surface maps but will talk about them from the perspective of the way air masses collide with one another. In some cases, these air masses lead to mid-latitude cyclones, which are different from hurricanes and tornadoes.

AIR MASSES Air masses are not the same thing as air cells. Air masses are generally large collections of air uniform characteristics, including temperature and humidity. If you can imagine these bodies of air as being giant blobs in the troposphere you can see where they would have edges. These edges are known as fronts; they represent areas where one air mass collides with another air mass. There is no such thing as an air mass that is not on all sides connected with some other air mass. You probably already know that most of the weather we experience happens along these weather fronts.

Air masses must come from somewhere. In this case, the origin of an air mass is called a source region. Source regions are areas where the winds are relatively stagnant so that the temperature and humidity can form and remain roughly the same throughout the entire air mass. Air masses are not something that stayed steady. They must form over region and then move to other regions. It takes several days for any given air mass to form and be stable. Most air masses represent areas of relatively high pressure and most have uniform humidity at the time they are formed. They essentially stay over a region long enough to acquire the characteristics seen on the surface of that region.

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In meteorological terms, there are ways we specifically describe air masses. An air mass that starts with a lowercase C indicates one that has developed over a continental landmass. Because there developing over a landmass, these are almost always dry. An air mass that starts with a lowercase M indicates a maritime air mass. This means that it forms over water. You can think of the letter M as meaning moist.

Figure 34.

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Now it is just a matter of defining where the air mass comes from. There are 4 letters choose from. If the code for the air mass answer with the letter a, that means it is from the Arctic. This can mean the North Pole or the South Pole. If you see the air mass ending with a P, it means it comes from the polar region. This is not the same as in Arctic region, but it still represents a colder area. The letter E means the airmass comes from an equatorial region. Finally, the capital letter T means the air mass is from a tropical region. You can now put these letters together to represent a typical air mass.

Figure 34 shows the different airmass types: Air masses, once formed, do not remain the same. As they travel, they can begin to change. For example, a colder air mass traveling over an area of warmth or more radiation of heat from the earth will now be warmer than it was in the beginning. The same is true of the humidity level of any air mass. If this happens, you would change the designation of the air mass.

The movement of an air mass depends on the upper level winds and not on any surface winds. They are of course bound by edges cold fronts. You already know that when a cold front passes through, cold air replaces warm air. The opposite is true when a warm front passes through. Air masses themselves are high pressure areas with little wind. At the edge of a front, it is windier as the air is being replaced. Stationary fronts are called stationary because the forces between two colliding air masses is so similar that the front is not moving much or at all.

Even though you see these fronts on a two dimensional surface map, you need to consider them to be in three dimensions. As always, warm air rises above cold air. When a warm front is passing through, there is a gradual slope from colder to warmer. When a cold front is passing through the slope the steeper, leading to stronger winds and more precipitation than you might see when a warm front passes through.

You will see precipitation in a warm front generally to the north of it, with layered cloudiness and milder precipitation compared to a cold front. Cold fronts have such a steep slope in temperature and precipitation levels between the two fronts usually thunderstorms, narrow bands of showers and windiness. Figure 35 shows three dimensional images of warm and cold fronts:

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Figure 35.

In the United States, there is a phenomenon called the dry line. This is a line that separates moist golf air from dryer air coming from the Pacific desert. It is a north-south line that often starts to travel eastward in the afternoon, which is when you will see storms developing in the southern Plains region. At night, it travels westward again only to repeat itself the next day. There is not going to be precipitation every day; it all depends on the characteristics of the air on either side of the dry line.

SOURCE REGIONS Source regions must be large enough to allow for big air masses to form. They also need to hang onto the air over them for a long enough period of time to have an effect on the entire mass. It takes a week for a 10 degree Celsius change to be distributed throughout an airmass from top to bottom. So, in a sense, the air needs to stagnate long enough to acquire stable characteristics.

There are six main categories of source regions around the earth. Two are warm and four are cooler. These include these areas: •

Sahara Desert—the air is hot and dry

•

Tropical oceans of any place on earth—the air is hot and wet

•

Arctic Ocean—the air is cold and wet

•

Siberia—the air is cold and dry

•

Upper Canadian territories—the air is cold and dry

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•

Southern oceans—the air is cold and wet

You should note that some of these areas are generalized rather than specific, such as the southern oceans and the tropical oceans.

WEATHER FRONTS There are four main types of weather fronts. We've talked so far about the warm front and the cold front. These are named according to the characteristics of the leading edge.

Warm fronts mean the leading edge of air is warm. These fronts are characterized more locally as the collision between two air masses that need to have differing temperatures and humidity levels. By definition, the warm one will be lifted above the cold one, regardless of which one is advancing.

A low pressure area develops where the two air masses meet. You will get the most precipitation if the lifted air mass is very humid. The lifted air should have condensation in the higher altitudes, giving rise to a great deal of precipitation. It is hard to get any storms without some type of front associated with them.

Stationary fronts can be due to some type of terrain issue, such as some sort of mountain range. It often rains in these areas, but it isn't usually very strong. You may see lighter rains, fog, or just drizzle. The front might break up as the air mixes together.

An alternative is that the front may become a warm or cold front if the power of one air mass exceeds the other.

Along a cold front, you will see a squall line, which is a line of severe thunderstorms, almost always associated with a cold front moving in. Once the cold air moves in, the high will develop and the air will be drier. It doesn't dry out but the airmass itself is simply drier to begin with. Winds die down but still blow somewhat toward the low region at the front.

Cold front weather depends strongly on your region and the time of year. In springtime, the winds tend to be stronger. During this time and into summer, you will get tornadoes or thunderstorms. You won't see such strong storms in the fall but you might get heavy

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rains without tornadoes. Extremely cold air masses in winter give rise to Artic air often preceded by snowstorms.

The warm fronts are gentler in nature when they occur as the warm air simply slides over the cooler and denser air that has less power overall. You can feel the transition more gradually with cirrostratus clouds seen rather than cumulonimbus clouds.

Snowflakes and gray skies are seen in the wintertime as the front approaches. A low pressure system is still generated with cold air initially beneath warm air. You will still feel coldness between the two air masses until the warm air overtakes the colder air. The worst weather is when the front goes through. Snow will become freezing rain and then rain will occur. It might be foggy until the front passes.

Occluded fronts are those where a cold front finally catches up to a warmer front. You might see airmasses to be cold, warm, and finally colder again. These are seen as purple line with triangles and half circles along the line. Because of the Coriolis effect, the front lines will curve with a low in the middle. Figure 36 shows these fronts. Remember that there is a low pressure system behind these fronts and not a high pressure system. There is very bad weather behind this front. Look for these along the Pacific coastline.

MID-LATITUDE CYCLONE STORMS Mid-latitude cyclones are of course seen in the middle latitudes, between 30 and 55 degrees North in the northern latitudes. Like all storm systems, these circle around low pressure systems but, in no way are these same thing tropical storm or hurricane. The differences are twofold. First, they are found in the mid-latitudes and not in the tropical areas of the world. Second, they are much larger than hurricanes and tropical storms.

How do these mid-latitude cyclones form? They seem to occur whenever there is much colder and drier air to the north and moisture warmer air and the South. Using the initials for air masses, you would label these a joining of CP and MT air masses. Due to the Coriolis effect, this boundary will begin to circulate in a counterclockwise direction.

Warm air is drawn further up and cold air is pulled down from the north. This is called the process of cyclogenesis.

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Because this is a circulating low-pressure system, you can imagine that all of the air is sucked inward similar to making a whirlpool in a bathtub or pool. While water will circulate going down a drain, air cannot do this so instead it rises upward. The upperlevel winds then take this cyclone and move it eastward. Ultimately, if the upper-level winds cannot cooperate, the cyclone will decay.

However, if the upper-level winds are more favorable, these cyclones will suck up warm air and bring down cold air. As the warm and humid air rises, a low-pressure system becomes deeper ahead of the cyclone. Behind the cyclone, the cold air will just fill in as it drops down for toward the south. As this air fills in, the cyclone simply gets pushed along to the east.

When a mid-latitude cyclone is completely formed, you will see small mini fronts radiating out from it. A mature cyclone has a deep low-pressure system in the middle and an occluded front developing whenever a cold front catches up to a warm front.

These occluded fronts are usually assigned that the cyclone is about to decay. They lose their strength and break up.

There are a few locations in North America where you will see these mid-latitude cyclones. They are commonly seen, for example, just east of the Rockies which would be the lee side. You probably know them by the names Alberta clippers or Colorado lows.

Alberta clippers move rapidly but have little precipitation, largely because they are dry.

Colorado lows have a large differential between the warm air mass and the cold air mass, commonly bringing air up from the Gulf of Mexico. These are associated with very bad weather such as sleet, heavy snows, strong thunderstorms, and blizzards.

You may also see these on the East Coast of the United States. Gulf Lows are seen in the south east and are associated with a great deal of rain or snow. This is because they are so close to a large body of water. The most severe storms of all are called Nor'easter's or bomb cyclones. These are so strong because they are formed with waters from the Gulf Coast as well as the colder waters of the Atlantic Ocean. These are extremely wet and have very strong low-pressure systems associated with them. The wind is intense, with these types of cyclones starting fairly quickly.

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In terms of storm tracks, Alberta clippers start out as low-pressure systems in the Gulf of Alaska and move along the border between Canada and United States. Colorado lows will develop near Colorado and travel up toward the Great Lakes. Gulf Lows begin in Louisiana and travel to the Northeast but do not spend much time over the Gulf of Mexico. Hatteras lows or nor'easter's begin in the Gulf of Mexico, picking up more moisture in the Atlantic Ocean, and then travel along the eastern seaboard of the United States.

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KEY POINTS FROM THIS CHAPTER •

Air masses form over source regions that may be wet, dry, warm, or cold.

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Air masses have relatively constant immunity and pressure throughout.

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It takes about one week or source regions to affect the air mass coming from it.

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Air masses can come from maritime or continental regions and can come from the equator to either pole.

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There are four different kinds of fronts that can form when two air masses collide in some way.

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Mid-latitude cyclones form in higher latitudes than regular hurricanes and are much larger.

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There are several known and named types of mid-latitude cyclones in the United States and North America.

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CHAPTER EIGHT: QUESTIONS 1.

From where would you expect an air mass labeled mT to come from as an example? a. Antarctica b. The Arctic Sea c. The Pacific Ocean d. Africa

2.

From where might you expect an air mass labeled CP to come from? a. Siberia b. Northern South America c. The mid-Atlantic region d. Africa

3.

What will you least likely see when a cold front is passing through? a. Thunderstorms b. Narrow precipitation band c. Layered, stratiform clouds d. Windy conditions

4.

What feature will you not see associate with the dryline in the United States? a. Moist air to the West b. Traveling eastward in the afternoon c. Retreat westward in the nighttime d. Narrow band of showers with progression

5.

Where on earth will you see the main hot and dry source region? a. Midwest America b. Sahara Desert c. Pacific Southwest d. Russia

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6.

Which area or source region on earth is most likely to lead to cold and moist airmasses? a. Arctic Ocean b. Antarctica c. Western Pacific d. Siberia

7.

In which type of front will the cold air mass be lifted above the warm air mass? a. When a warm front is advancing only b. When a cold front is advancing only c. When a cold or warm air front is advancing d. In no situation

8.

In the springtime when a cold front is approaching, which characteristic of the weather will you most expect to see? a. Drizzle with fog b. Strong windy thunderstorm c. Blizzard followed by arctic air d. Long stretches of heavy rains

9.

Using the initial naming convention for air masses, name which two air masses form mid-latitude cyclones? a. CA and CT b. CP and CT c. CA and MT d. CP and MT

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10.

If you look at the air patterns in a mid-latitude cyclone, you will see what particular pattern? a. Moist warm air extending upward to the right on the weather map with cold dry air extending downward to the left. b. Moist cold air extending downward to the left of the cyclone on the weather map with warm moist air upward on the right. c. Cold dry air extending downward on the right-hand side of the cyclone with warm moist air extending upward on the left-hand side of the cyclone. d. Warm moist air drawn upward on either side of the cyclone.

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CHAPTER 9: WEATHER FORECASTING Are you ready to predict the weather? In this chapter, you will study how weather information is gathered in order to ultimately predict it. You will learn how large organizations like the National Weather Service use supercomputers to forecast your weather. We will look again at surface maps in order to see how these can be used for weather prediction. Finally, we will study the different weather terms you need to know and the types of watches and warnings sent out every day across the world when there is severe weather.

GETTING WEATHER INFORMATION The National Oceanic and Atmospheric Association or NOAA has the National Weather Service under it. These are the people who monitor the entire atmosphere around the earth and study how this impacts the weather. At one time, information could be gotten from all sorts of weather stations around the world, however, making accurate predictions was very difficult. Now, using numerical forecasting and supercomputers, it is possible to predict the weather far out in advance. Let's look at the different tools used by major meteorological agencies to forecast everyone's weather.

Doppler radar is one of the best tools for both predicting and following severe weather systems. The term Doppler means flow so when you hear any talk of a Doppler system, you know that what it is measuring is the flow rate of something. In this case, meteorologists are measuring the flow rate of the air patterns around the earth. This becomes very important in studying tornadoes, hurricanes, and thunderstorms. These types of radar systems can predict both the flow rate and direction of wind systems.

Satellites are also used throughout the world to monitor the weather. You have probably seen these images, which show things like clouds, the oceans, and squall lines. There are several kinds of satellite systems. There are orbiting satellites called polar satellites that take about seven images per day near the earth's surface. Geostationary satellites move

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according to the earth's own orbit in order to stay essentially in the same place all the time. They are much higher in the sky images about thirty seconds apart and there are enough of them to capture the whole globe. There are also deep space satellites that face the sun. We need them to capture solar storms as well as other space weather phenomena. There are miscellaneous satellites operated outside of the National Weather Service sometimes used to gather more information.

The geostationary satellites are not really stationary but hover high above the earth at approximately twenty-two thousand miles above the earth's surface. These are the ones you tend to see on the news showing the cloud pattern in a given area. As mentioned, they take very frequent pictures of the same place on earth. Figure 36 shows the kind image these satellites create:

Figure 36.

The polar satellites travel in what can be called the spiral direction from pole, able to capture images of the entire planet just once in a day. There are four images taken of the daylight taken at night. Because they are much closer to our earth, just five hundred

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miles above the earth's surface, they can show things like wildfires, volcanoes, and even mudslides.

We have already talked about radiosondes. You need to know that these are still important to weather forecasting, because they can capture information from many levels of the atmosphere in a short period of time. In the United States alone, there are about ninety-two locations where radiosondes are released in weather balloons twice daily. It takes two hours for these weather balloons to reach the upper stratosphere.

While these are functional, they gather information on the temperature, humidity, air pressure, wind speed, and wind direction. Certainly, they are sent out more frequently during storm systems.

Another tool is called the ASOS or automated surface observing system. These monitor weather continuously with more than nine hundred stations throughout the United States. While these are automated, they can check precipitation, surface temperature, wind speed and direction, sky conditions, and surface visibility up to twelve times per hour. These are manned by nearly 10,000 volunteer workers that collect data on things we need to know about, such as snowfall and rainfall information. They do not necessarily forecast the weather but they do give us information for improving forecasting in the future.

We could not get anywhere with such accurate forecasting without the supercomputers they have at NOAA. As you can imagine, they need to pick up data from all over the world, including surface stations, radiosondes, satellites, and buoys. There are roomfuls of supercomputers that together collate the information in order to make accurate predictions. They use the numerical weather forecasting model, which essentially means they crunch the numbers from the data they are given.

One particular system of computers is called the advanced weather information processing system or AWIPS. The system takes all of the known data and formatted into a graphical interface. This allows the forecasters to look at the information on maps, to read the forecast, and issue watches and warnings for severe weather. Weather maps are complex and are best generated with this kind of efficiency.

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COMPUTERIZED WEATHER FORECASTING As mentioned, we now use the numerical weather prediction system or NWP. Historically, forecasters would take information from past years and try to make predictions in the weather in the current year. This is not terribly accurate. Nowadays, current daily data is fed into computers, analyzed, and organized in a way that allows for the best weather predictions. You need computers to be able to access the surface data as well as the data gotten from high in the sky using radiosonde information.

The GDAS is also called The Global Data Assimilation System. This takes from twentyone separate weather forecasts to get global weather coverage and a forecast that is now able to be gotten for sixteen days in the future. Without the ability to collect information from the different parts of the world, we would not be able to make this kind of forecast so far in advance.

There are many other forecasting systems in use. The Global Forecast System uses different models to give an accurate assessment of current weather systems and conditions on all parts of the globe. The Climate Forecast System can help determine the seasonal forecast nine months in advance. The North American Mesoscale is regional to North America and can get very specific about the weather to a resolution of about eight kilometers. The Rapid Refresh is able to get very specific about a forecast in a given area hour by hour for up to eighteen hours in advance. Finally, the Navy operational global atmospheric prediction system is able to get vertical resolution of the air pressure above and below the sea level.

USING SURFACE CHARTS A synoptic surface chart is the surface chart used to detect the weather at any given point in time. We use these charts to be able to see what the weather might look like in advance. A synoptic surface chart is created and sent to the states every three hours. As you know, it shows the areas of high and low pressures, temperature ranges, fronts, wind speed and direction, dewpoints, and local weather conditions. For pilots, visual obstructions are noted.

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If you were a pilot, for example, you did a map showing all of these things and an interpretation of them using a surface analysis chart. Figure 37 shows part of this chart.

As you can see, it is simple numbers and figures to describe the local conditions:

Figure 37.

Figure 38 shows a good weather depiction chart:

Figure 38.

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A good chart will show the highs, lows, fronts, and isobars so you can see the strength of the prevailing winds in a certain area of the world. These charts can be gotten every three hours for meteorologists and aviators to use in order to be able to safely fly. They should also indicate where snow and rain are located and areas where you might see a mixture of snow and ice or freezing rain. They do not show temperature.

Weather prognostic charts will show the weather for an area from the surface to an area above it up to 24,000 feet for low-level events and up to 63,000 feet for high-level events. Low level charts are used for aviators in order to detect hazards when flying.

These are released for aviators 4 times daily. They can forecast the weather into 12 and 24-hour intervals so you can look ahead to see what you can expect. Newer maps can predict the weather for aviators up to 48 hours in advance.

SENDING OUT WATCHES AND WARNINGS If every single day was sunny and warm, the job of a meteorologist wouldn't be terribly interesting. Fortunately, few places in the world are like this. There is always something fun to talk about in most regions when it comes to meteorology. Before you can be good at this part, you need to learn some storm lingo. After this, we will talk about the types of storm watches and warnings you may encounter as well as what they mean:

REPORTING ON THUNDERSTORMS We will talk more about thunderstorms in an upcoming chapter. Until then, let's learn some important thunderstorm terms to get you going: •

Anvil cloud – you may have seen these before. They are tall thunderstorm clouds ravaged by upper winds. The top gets sheared off so it looks like an anvil on top.

Anvil clouds spread out this way often spread further than 100 miles downwind from where they started. Figure 38A shows these clouds:

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Figure 38A. •

Downburst – this is a sudden downward burst of cold air often reaching the ground at 70 miles per hour at their peak. These are damaging straight-line winds often associated with heavy downpours. You need airplane surveillance to see that these aren't tornadic winds.

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Downdrafts – these are columns of sinking cold air, usually with rain near the beginning of a cold front.

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Flanking line – These are cumulus clouds in a line that extend out from a stormy cumulonimbus cloud, often on the southwestern side of the storm. If you see these, they predict strong thunderstorms as part of the incoming front.

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Funnel cloud – this is any funnel-shaped cloud that comes down from a thunderstorm cloud; they are due to rotating air columns containing condensed droplets of water. They are not usually dangerous.

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•

Gust front – this is the leading edge of the downdraft coming down from the thunderstorm. You will feel a sudden gust of cold air just before the rain begins.

These are not as dangerous as downdrafts or downbursts.

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Hook echo – this is a pattern seen on Doppler radar on the southwest side of a storm. If you see this echo, there is a strong chance of tornadic activity within it.

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Macroburst – this is a very large downburst extending as far out as 2.5 kilometers in diameter. These can be extremely damaging to whole towns and cities.

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Microburst – This is a small downburst that only ranges from 0 to 2.5 kilometers in length.

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Mammatus clouds – These look like hanging breasts from a cloud. It is often seen under anvil clouds. They do not cause thunderstorms but accompany them instead.

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Precipitation shaft – this is a visible column of hail or rain that you can actually see falling out of a cloud.

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Rain-free base – this is the underside of a storm cloud that has no rain coming out of it. This is because there is an updraft in the area.

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Roll cloud – these are rare clouds that come out of shelf clouds, caused by warm air moving up and over cool air and back under again. The cloud takes on the shape of a horizontal tube that detaches from the leading edge of the main thunderstorm.

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Scud clouds – these are low level clouds seen behind gust fronts that are not tornadoes but are so low as to be worrisome to some viewers. They are not dangerous to people or property.

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Shelf cloud – these are low clouds that are shaped like wedges and attached to thunderstorm clouds. They are seen above gust fronts and represent warm air riding over cool air but not completely over, as is seen with roll clouds.

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Updraft – this is a column of warm and moist air that rises in association with thunderstorms. This warm air condenses as part of cumulonimbus clouds and

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helps to fuel the thunderstorm. This updraft ranges from approximately forty kilometers per hour to up to one hundred kilometers per hour, depending on the thunderstorm strength.

•

Wall cloud – this is a sudden lowering of the thunderstorm cloud along the line between rain free air and the thunderstorm. This cloud is attached to the thunderstorm cloud and may rotate, causing a tornado.

TERMS RELATED TO FLOODS if you live in an area where there is flooding, you will need to understand several terms if you are to report the weather. Here are some common flood related terms: •

Bankfull - this is the tallest height a river can reach before it overflows along its banks. A person who lives in this type of area may experience damage to the property if the Bankfull is exceeded; however, some rivers can accommodate this overflow.

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Coastal flooding – you will see this along ocean coastlines. They can be associated with high or persistent winds offshore, high tide areas, or a storm surge prior to a hurricane.

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Flash flooding – this is a sudden flood that you often see after a dam breaks or after heavy and sudden rainfall. These especially affect the smaller creeks that can easily overflow their banks and flood the land large distances away from their shores.

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Flood stage – the flood stage is different from the Bankfull. A river can overflow its banks but not cause anything near the flood stage. The flood stage depicts the height of water necessary to cause some type of property damage in the area.

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Urban flooding – this is flooding after a heavy rainfall in urban areas, largely because there is a lot of pavement that cannot absorb so much water in such a short period of time. These can become dangerous to pedestrians and automobiles.

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TERMS RELATED TO WINTER WEATHER If you live in an area where there are winter weather phenomena, you will need to know how to describe these and what they mean. Here are some terms to know: •

Blizzard – this is found at any winter weather with strong winds and heavy snow.

The winds must be greater than thirty-five miles per hour be called a blizzard.

There used to be a temperature criterion for blizzards that is not used anymore.

•

Blowing or drifting snow – blowing snow may or may not be due to snow that is actually falling at the time. It is called drifting snow if the winds are strong enough to cause the snow to build up certain areas.

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Freeze – this involves temperatures near the ground that are about thirty-two degrees Fahrenheit or colder. Agriculturists often use the term hard freeze or killing freeze to indicate severe crop loss.

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Frost – this involves scaly ice crystals, although they may be needle shaped or fan-shaped. They are similar to dew drops except that the temperature has fallen to approximately thirty-two degrees at ground level.

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Heavy snows – you call it heavy snows by the amount of snow accumulation per hour. If there is snow that falls at least six inches over twelve hours or 0.5 inches per hour, this will be a heavy snow. It does somewhat depend on where you live, however. If you get just six inches in twenty-four hours in the southern United States, it could be called heavy snow.

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Ice storm – you would call the storm an Ice storm if ice accumulates in the form of freezing rain on the ground or on vegetation. It is called significant if at least one half inches of rain and ice attach to vegetation and roadways.

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Snow flurries – you would call a storm system a snow flurry if there was a brief period of snow without any significant accumulation. In a snow shower, the snow is brief but a bit more intense; there may or may not be accumulation.

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Snow squalls – this is an intense dumping of snow with strong winds and potentially a high level of accumulation in a short period of time.

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•

Wind chill – this is called the wind chill factor or wind chill index. This is a number gotten by the absolute temperature outside plus the amount of wind in the area. It gives you a better example of how much faster your skin would freeze compared to low temperatures without wind.

SEVERE WEATHER WATCHES AND WARNINGS Now that you know something about bad weather, let's look at the types of watches and warnings you would issue when bad weather threatened others. We will talk much more about some of these weather issues in a later chapter. As you know, many storm related events are posted in the media as advisories, watches, or warnings. You will need to know the difference between these different designations.

There are several broad categories of watches and warnings according to the National Weather Service. These include the following: •

Severe local storms – these can be any local storm, such as a tornado or thunderstorm

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Winter weather – these would be any alerts related to winter weather phenomena, such as sleet, snow, or ice.

•

Fire related weather – these include giving warnings when it is likely that fire could develop.

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Flood related weather – these can be related to coastal flooding or river flooding.

You can also include urban flooding as part of this.

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Coastal or Lakeshore hazards – these are things related to living near a shore line and can also include riptides and high surf warnings.

•

Marine hazards – this could include freezing spray or any type of hazardous sea travel experience.

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Tropical cyclone hazards – these can include storm surges, marine-related tornadoes, or any marine related winds that could cause property damage.

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•

Hazards unrelated to precipitation – these include extremes in temperature, fog related events, high winds, or localized flooding unrelated to rain.

WINTER-RELATED ADVISORIES Here are some watches and warnings related to winter weather.

Winter weather advisory – this means that some type of winter weather event is either occurring, about to occur, or probable. This is what used to be called a Travelers advisory. It indicates any type of winter precipitation that could impact travel or cause a major inconvenience. This advisory has largely replaced the blowing snow advisory and snow advisory.

Winter storm watch – this means you can expect the possibility of winter weather within two days. It is not guaranteed there will be a snowstorm.

How do you define hazardous winter weather? It is defined in one of several ways: 1. At least five inches of snow or sleet in twelve hours 2. At least seven inches of snow or sleet in twenty-four hours 3. Accumulation of ice that could damage powerlines or trees 4. Any combination of damaging winds, snow, and or ice that is life-threatening There will be some variation in the characteristics of snowfall or sleet conditions that qualify as an advisory, watch, or warning depending on where a person lives.

Winter storm warning – this indicates winter weather that is either occurring or imminent within the next 12 to 48 hours. Note that it could just as likely to be imminent as it is to be already present. You can expect freezing rain, strong winds, sleet, and or snow. The exact amount varies from place to place throughout the country. This has replaced the sleet warning and the heavy snow warning that used to be commonplace.

Ice storm warning – this is released whenever it is expected that ice will accumulate cost travel and utility disruptions. Ice is heavy and will frequently down power lines and trees. Accumulations vary from ¼ to ½ inch of freezing rain.

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Blizzard warning – a blizzard warning means that there will be gusts of wind greater than thirty-five miles per hour, along with heavy snowfall and reduced visibility. The length of time for a blizzard is at least three hours. As mentioned, there are no temperature criteria. You can issue a Winter storm watch for blizzard conditions if you expect such a storm to happen within 12 to 48 hours.

Lake effect snow warning – this is usually a warning used for regions where lake effect snows are possible. The expectation is of at least six inches of snow in twelve hours or less. Alternatively, it could mean eight inches of snow in twenty-four hours or less. The warning is given when this precipitation is imminent or highly likely.

Snow squalls warning – this is an intense winter storm of limited duration with the expectation of at least moderate snowfall according to radar. Expect reduce visibility of less than one fourth mile, white out conditions, lightning, extreme temperature drops, and strong surface winds.

The National Weather Service no longer uses sleet warnings, sleet advisories, snow advisories, blowing snow advisories, blowing and drifting snow advisories, or extreme cold watches or warnings. They have also deprecated lake effect advisories and watches as well as blizzard watches and freezing rain advisories. These have largely simplified the winter storm advisories.

TORNADO AND THUNDERSTORM ADVISORIES These are watches and warnings related to spring through fall weather and related to severe storms in the continental regions.

Tornado watch – this means there are favorable conditions for the development of either severe thunderstorms or tornadoes. They are often valid for between five and eight hours.

Particularly dangerous tornado watch – this indicates favorable chances for very destructive storms or tornadoes. They are commonly issued when a major tornado outbreak could happen or when there is the potential for violent category tornadoes.

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These are valid for longer periods of time than regular watches and often involve a wider swatch of the country.

Tornado warning – this indicates Doppler radar detection of rotation or the siting of a tornado by special spotters or by law enforcement. These are often issued for thirty minutes that can extend for as long as an hour. You do not need to have a tornado watch in order to have a tornado warning.

Particularly dangerous tornado warning – this indicates a large and severe tornado has been confirmed and is moving through an area that has already been warned. It is often a reissuance of a prior tornado warning and can be a situation where a severe tornado has already damaged property and is expected to do similar damage as it moves along.

Tornado emergency – this is an unofficial warning issued to heavily populated areas when severe F5 tornadoes are headed toward these areas. They have been issued in the past when severe tornadoes have damaged areas like Oklahoma City, Greensburg Kansas, and Tuscaloosa, Alabama. This is the highest level of tornado warning alerts possible. It indicates the greatest potential for loss of human life because major metropolitan areas are involved.

Severe thunderstorm watch - what this means is that the conditions are right for a severe thunderstorm to develop. This means the potential for high winds, hail, and significant rain as well as tornadic activity. They are valid for up to eight hours in the future.

Particularly dangerous situation severe thunderstorm watch – these are issued for a longer period of time and severe thunderstorm watches and usually involve a larger area. It also means that conditions are right for severe thunderstorm activity and isolated tornadoes. It is reserved for thunderstorm activity over a larger area as well.

Severe thunderstorm warning – this indicates a known thunderstorm on Doppler radar or one that has been sighted by spotters. You can expect hail that is one inch in diameter or larger, damaging winds in excess of fifty-eight miles per hour, and heavy rains. The total duration of these warnings is thirty minutes to an hour. You do not need 105

a watch in order to have a warning. These can be upgraded to tornado warnings, depending on the situation. Lightning is possible but is not a requirement to have this type of warning.

Particularly dangerous situation severe thunderstorm warning – this is similar to other particularly dangerous situation warnings in that it usually indicates a larger area is involved and also indicates the possibility of fatalities and significant property damage to a larger swath of a state or part of the country. You might expect winds greater than eighty miles per hour or hail greater than three inches in diameter.

Severe thunderstorm emergency – this is a high end thunderstorm warning sometimes issued when a severe storm is bearing down on a large metropolitan area or other heavily populated area. A warning of this type was first issued in 2019 when a thunderstorm approached Cheyenne, Wyoming. Clear criteria for this emergency have not yet been established.

Significant weather advisory – this is issued when a severe storm is expected that is not as strong as one would issue in a severe thunderstorm warning. It usually means that you have detected a storm on Doppler radar or that one has been spotted; however, the hail is not as large and the winds are not as strong as you would see in a severe thunderstorm warning.

Severe weather statement – this is simply a revision warning to help the public understand the storm in greater detail. It could indicate that you are canceling a prior warning or that you have heard of specific damage in a certain area. It could also mean that you are allowing a warning to lapse.

Flash flood watch – this indicates favorable conditions for other urban flooding or flash flooding within the next thirty-six hours, although it is often issued about twentyfour hours in advance of any expected flood.

Particularly dangerous flash flood watch – this indicates extremely high levels of flooding and often span multiple counties or an entire state. As you have noted, when a watch or warning indicates that it is particularly dangerous, it often means that a larger area is involved, although it could mean that a more severe situation is pending.

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Flash flood warning – this indicates that a flood is imminent, highly likely in the short term, or ongoing. Remember that a flash flood occurs within six hours of any excessive rainfall event and that it poses a threat property or life. It can also occur because of dam failures or because of an ice jam.

Particularly dangerous situation flash flood warning – this is similar to other particularly dangerous situations in that a larger population is affected by this flash flood.

Flash flood emergency – this is similar to other emergencies in that it is widespread and involves a heavily populated area. One example of this was during hurricane Harvey in 2017.

You may also issue one of several warnings and watches associated only with flooding.

These include area flood warnings, watches, or advisories. These types of statements apply to streets, streams, rivers, or urban storm drains. River flood warnings and advisories apply to rivers or large streams and are related to the flood stage. You could also issue an urban and small stream flood advisory after a large rainfall. Any flood statement simply means you're trying to warn the public of an ongoing threat or even a cancellation of a previous watch or warning.

FIRE-RELATED WEATHER EMERGENCIES While fires and weather are not the same, the system in place for weather fits well for these types of emergencies as well. These are the watches and warnings you might expect to issue: Fire warning – this indicates you have determined that there is a major uncontrolled fire in a populated area or near major roadways.

Red flag warning – this indicates a situation extremely favorable for this rapid spread of wildfires within the next twenty-four hours. They issue this when there has been limited precipitation, low relative humidity, and higher winds above twenty miles per hour expected.

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Extreme red flag warning – you would issue this in situations where conditions were the same as a red flag warning but to indicate a much more serious condition. This was first introduced in October of 2019.

Fire weather watch - this is issued when you expect the conditions to be favorable due to dry vegetation in the future. You can issue this up to seventy-two hours in advance of this expectation. The idea is usually to warn those responsible for controlling the spread of fire.

COASTAL OR LAKESHORE HAZARD WARNINGS There are specific watches or warnings associated with coastal areas and the people who live near them. Here are some of these: Coastal flood warning – this indicates water coming inland from any major storm near the coastline. It indicates an ongoing problem or one you expect to occur within the next twenty-four hours.

Coastal flood watch – you would issue a watch if you expected flooding in a coastal area within forty-eight hours.

Coastal flood advisory – this is issued for minor flooding or tidal overflow in a coastal area within twelve hours. It is not expected to cause any threat to property or lives but will be a nuisance.

Storm surge warning - this is usually issued because of a hurricane or other tropical cyclone. As you will learn there will be storm surge waves ahead of this type of serious weather phenomena. A warning is issued at a maximum of thirty-six hours ahead of the expected event. You would also issue a storm surge watch if this type of event might happen within forty-eight hours.

There are several similar watches and warnings you would issue related to living on the coastline of a lake. These include Lakeshore flood watches, advisories, and warnings.

There is a special warning given to those living in the Great Lakes region. This is called a Seiche warning. This indicates wide fluctuations in the water level in your area, similar

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to what you would see with a bit of sloshing back and forth. The water might be extremely low at one point and very high shortly thereafter.

There are specialized warnings related to windiness near a lake. These are lake wind advisories, watches, and warnings. The cut off for watches and warnings is sustained speeds of forty miles an hour, while the cutoff with lake wind advisories is between twenty and twenty-nine miles per hour.

If you live in an area where there is surfing, you might issue a surf warning. There are high surf advisories, watches, and warnings. Each of these indicate some type of surfing danger. When a warning is issued, it means the surf will be destructive, while a watch indicates the potential for breaking waves in the next several days. You might also issue a statement for rip currents in the area or simply a beach hazard statement, which could indicate any life-threatening event at a beach including riptides, water related chemicals near the beach or other life-threatening conditions.

MARINE HAZARD WATCHES AND WARNINGS If you lived in an area where there was an ocean or sea, you might release some type of Marine hazard statement. These could include heavy freezing spray watches and warnings or freezing spray advisories. These are related to the deposition of frozen water on ships, which can be hazardous with these types of vessels. There are also hazardous seas watches and warnings that can indicate rough surf or high waves in a given area.

Low water advisories are sent out in the Great Lakes or other areas where waterways might be too low for vessels to travel through.

Marine weather statements and special Marine warnings indicate some type of serious weather or an ocean or sea. It could mean an offshore waterspout, thunderstorm, or other serious but short-term Marine event. There are special advisories for small crafts.

You would issue a small craft advisory with or without special circumstances such as winds, hazardous seas, or rough bars. These are specifically designed for small craft operating in large bodies of water.

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ADVISORIES RELATED TO TEMPERATURE You might want to release a weather statement related to excessively high or low temperatures in a given area. We will talk about the heat index at a later time, however, this index and the wind chill index are important factors to consider when you make a weather statement. Let's look at some common temperature related watches and warnings.

Excessive heat warning – this indicates that the maximum indices are expected to be exceeded, according to locally defined criteria. Meteorologists release this warning any time they expect more than three hours of high heat in the next forty-eight hours and would try to be reset within twelve hours of onset of the high heat. In most cases, it means temperatures above 105 degrees Fahrenheit and nighttime temperatures above seventy-five degrees Fahrenheit.

Excessive heat watch – this is released when you expect conditions to be favorable for the development of high heat conditions within the next seventy-two hours.

Extreme cold watches and warnings – you would release this type of warning if the temperatures in the air are less than forty degrees Fahrenheit for three or more consecutive days. This type of watch and warning are only issued currently in Alaska.

Freeze watches and warnings – these are released when the shelter temperatures are expected to be thirty-two degrees or lower. You issue a watch when conditions are favorable for this type of event within forty-eight hours and a warning when this type of event is expected within the next 12 to 36 hours. These are issued primarily in agricultural regions to help farmers know that the potential for crop loss is there during a growing season. Hard freeze watches and warnings indicate temperatures below twenty-eight degrees Fahrenheit or when a large area is involved.

Frost advisory – this is advisory issued during a growing season when the minimum sheltered temperatures are expected to be between thirty-three and thirty-six degrees Fahrenheit over a large area. You would not issue this type of warning or advisory outside of the growing season.

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Wind chill watches and warnings – windchill advisories are related to the perception of cold on the skin and to the damage the combination of wind and cold can do on individuals. A wind chill warning means you expect to see severe frostbite or hypothermia from this combination. The criteria for windchill advisories vary from place to place. In 2021, the wind chill warning has been replaced by what is called the Extreme Cold Warning Product. This advisory will include the combination of cold and windchill rather than just the windchill. In general, a particularly dangerous situation windchill warning means that the windchill is less than forty degrees Fahrenheit.

TROPICAL WATCHES AND WARNINGS We will talk more about hurricanes in the next chapter. For now, we will talk only about the watches and warnings you might send out.

Tropical Storm Watch or Warning – this type of watch or warning means you expect a tropical storm. By definition, a tropical storm as conditions where the wind is as high as seventy-two miles per hour and as low as thirty-nine miles per hour. It could also mean you expect a storm surge and/or coastal flooding. A watch is issued only when the conditions are right and such a storm is possible.

Hurricane watches and warnings – this type of watch or warning is issued when you expect winds greater than seventy-four miles per hour. A warning is issued when you expect this type of storm within thirty-six hours. In areas like Guam, a typhoon warning is issued instead. A hurricane local statement is given when you are trying to tell the public specifics about a hurricane, such as evacuation measures and special precautions. You would indicate an extreme wind warning if you expected winds in excess of 120 miles per hour, usually seen in the eye wall of a significant hurricane.

These need to be issued within two hours of the expected event.

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KEY POINTS IN THIS CHAPTER •

There are many ways to gather the weather the information necessary to make weather predictions. Most of these involve gathering information from numerous areas around the world.

•

Computerized equipment is used to collate all of the information gathered into some type of cohesive unit.

•

Surface maps are used to show the current conditions, but you can also use them to make predictions in advance.

•

It is possible to predict the weather as far in advance as fifteen days.

•

Memorize the statements related to the different types of inclement weather.

•

Watches, warnings, advisories, and statements indicate different levels of concern related to the weather forecast. Weather emergencies are particularly severe as they involve areas that are heavily populated.

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CHAPTER NINE: QUESTIONS 1.

In what area of the weather would you least likely make use of a Doppler radar system? a. Studying hurricanes b. Studying thunderstorms c. Studying the climate d. Studying tornadoes

2.

Which satellites do we use to monitor incoming solar storms? a. Geostationary satellites b. Surface satellites c. Polar satellites d. Deep space satellites

3.

What will you likely not see on a synoptic weather chart or map? a. Temperatures b. High and low pressure systems c. Dewpoints d. Seven day weather forecast

4.

You have gotten a surface analysis chart of local weather in your area. What kind of information will you not get out of this chart? a. Temperature b. Rainfall amounts c. Cloud cover d. Barometric pressure

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5.

You are forecasting the weather and you note a blizzard is coming. How would you define this winter weather phenomena? a. By the amount of wind generated only b. By the amount of snowfall gotten in the storm c. By the wind chill factor associated with the storm d. By the degree of low-pressure you get in the eye of the storm

6.

You are outside and are concerned about severe weather in the wintertime.

Which type of severe weather phenomenon would you be most concerned about? a. Snow flurry b. Snow squall c. Heavy snow d. Snow shower

7.

You decided to issue a red flag warning with regard to the fire risk. What criterion is not likely to be a part of this? a. Ongoing wildfire b. Winds expected to be higher than twenty miles per hour c. Low relative humidity d. Limited recent precipitation

8.

Which type of weather advice would you issue when you are canceling a previously issued storm watch or warning? a. Advisory b. Statement c. Cancellation d. Emergency

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9.

What is the cutoff above which you decide to issue a hurricane warning versus a tropical storm warning? a. Sixty-five miles per hour b. Seventy-four miles per hour c. Eighty-seven miles per hour d. Ninety-six miles per hour

10.

In which part of the United States and its territories would you not issue a hurricane warning in the event of the cyclone? a. Guam b. Puerto Rico c. The US Virgin Islands d. South Carolina

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CHAPTER 10: THUNDERSTORMS AND TORNADOES In some parts of the world, phenomena like thunderstorms, floods, and tornadoes are commonplace. In this chapter, we define these weather issues and talk about how they develop. While thunderstorms and tornadoes are generally interconnected, floods can have many causes unrelated to some type of storm. These are all devastating weather occurrences that damage property and cost many lives as they rip through an area.

THUNDERSTORMS Thunderstorms are also called lightning storms or electrical storms. They are associated with the combination of lightning and thunder. As you know, they come from cumulonimbus clouds, which are high enough to have these effects. Thunderstorms are associated with high winds, heavy rains, and or hail, snow or sleet. You may see no precipitation at all in a few cases. They often line up to produce a squall line or rainband. Supercells are particularly severe and have rotational qualities.

You may see thunderstorms anywhere on earth but most commonly in areas where warm and moist tropical air travels away from these areas toward cooler parts of the world. Where cold and warm are meet are exactly where you see these storms. As you will see, damage can occur for many reasons from thunderstorm activity, causing property loss and sometimes loss of life.

LIFE CYCLE OF A THUNDERSTORM Thunderstorms have a certain life cycle or pattern of development. They tend to occur the most when there is a sharp updraft of warm air that rises into and above air coming from the polar regions. The warm air is moisture-laden and because it cools, the water vapor condenses. The cumulonimbus clouds are tall so the updrafts have a place to drop as much moisture as possible into the cloud. Lightning and thunder happen because the air is unstable.

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There are three main conditions to consider in order to have a thunderstorm. These are adequate moisture, an unstable mass, and the lifting force of heat. Let's look first at the initial developing stage of a thunderstorm.

The first step is to have an uplifting of moist airmasses into the higher levels of the atmosphere. These masses require input from the sun onto the ground. The ground radiates heat that is lifted up to higher elevations and toward a mass of cooler air.

Cumulus clouds are in this first stage, showing up because of condensation of water vapor. Remember that condensation gives off heat by itself so that the air is lifted further through convective processes. When the warmed air leaves the lower aspect of the clouds, low air pressure is left behind. Huge amounts of moisture enter the atmosphere.

After this, the thunderstorm is considered mature. Anvil clouds can be seen and warm air rises until it reaches the tropopause. Cumulus clouds become cumulonimbus clouds and air is forced to spread below the tropopause out from the center. The raindrops get much heavier and often freeze into ice particles. These will fall and melt to become rain.

Prolonged updrafts will lead to ice so large that hail results. The coexistence of updrafts and rain-drenched downdrafts mean the thunderstorm is mature. Inside the clouds is turbulence and the chance for wind, lightning, and tornadoes.

The storm may simply rain out as long as there is little wind shear. The dissipation starts when the downdrafts exceed the updrafts. This can happen quickly unless there is a supercell. The downdraft will push through the clouds and often hit the ground. With nowhere to go, the air spreads out. You will call this a downburst. Such a strong cold downburst blocks any updraft from occurring. The thunderstorm can't sustain itself.

These downbursts are potentially damaging to aircraft flying within them. The craft can lose their lift or can be damaged in windshear.

CLASSIFICATION OF THUNDERSTORMS Thunderstorms come in four varieties. These are called single-cell storms, multi-cell storms, squall lines, and supercells. The simplest among these are single-cell storms,

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having very little vertical windshear associated with them. These last less than 30 minutes.

The other types of storms are more organized and last longer, with a great deal of windshear in excess of 13 meters per second. There are strong updrafts and severe weather phenomena like hail and extreme winds. Supercells are particularly strong and linked to hail, wind, and tornadoes. There is a great deal of energy in these types of storms.

Single-celled storms have one major updraft. These are called air-mass thunderstorms, typically seen on summer days. They can come after a cold front has come in from the ocean in wintertime. By definition, a cell is defined as a single updraft. Some of these are called pulse severe storms if they have severe weather and short durations associated with them.

Multi-cell clusters involve more than one updraft; there is a mature thunderstorm in the middle with dissipating storms downwind of the main storm. Clusters can organize into squall lines. Each cell may last only 20 minutes, but the clusters altogether last several hours at a time. Strong cold fronts and mountain ranges may help form these larger clusters, capable of moderate hail, flooding, and minor tornadoes.

Squall lines are linear and consist of multiple cells that have lined up along or ahead of a cold front. Expect heavy precipitation, lightning, hail, straight-line winds, waterspouts, and tornadoes. Where you see a bow echo on Doppler radar is where the straight-line winds emerge. Bow echoes known as derechos can move very quickly.

Supercells are very large storms associated with windshear. Windshear is associated with changes in windspeed and direction with the height of the storm. There will be many different updrafts and downdrafts with these storms. These create the strongest storms where the winds can break through the tropopause to enter the stratosphere. The storms may be up to 15 miles in width. Surprisingly, up to 10 percent of these do not have severe weather as part of them, although most do. There can be rotating updrafts in them, called mesocyclones. Most tornadoes come from these kinds of thunderstorms.

You would designate a thunderstorm as severe if there are winds greater than 58 miles per hour or hail up to one inch in diameter. If you see tornadoes, you would upgrade the 118

storm to a tornado warning rather than a severe thunderstorm warning. In Canada, you would add a criterion of more than 2 inches of rain in one hour as indicating severity.

MESOSCALE CONVECTIVE SYSTEMS Thunderstorms become very complex when they form mesoscale convective systems.

These are organized complexes of thunderstorms that have some power behind them, although less than mid-latitude cyclones. These weather systems can last for many hours. They are responsible for things like squall lines, polar lows, lake effect snows, and full-blown mesoscale convection complexes. You will see these more commonly when there is a large difference between daytime and nighttime temperatures. This is what causes them to develop overnight.

There are similar systems in the tropics, near the Intertropical Convergence Zone, usually when it is the warmest. They tend to be more powerful over land, except for those that cause lake effect snows. Polar flows happen from these systems in the higher latitudes when it is cold. There can be one parent thunderstorm and many secondary storms that can develop as the initial one dissipates.

HOW DO THUNDERSTORMS MOVE? There are two ways that thunderstorms move. One is through advection, where wind travels outward from the storm, often finding more areas of heat and wetness to draw upon. The other is simply being moved along with the prevailing winds. If two thunderstorms merge, they often take on the movement patterns of the larger storm. If the mean wind in the troposphere is strong, this will be the predominant way that thunderstorms move along.

FLOODING Flooding happens when water flows over usually dry land. This is a natural phenomenon made worse by human influence, such as deforestation and poor land management.

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Levees and dams can contribute to this problem and climate change is not helping. Sea levels are rising, which will contribute to coastal flooding.

There are several types of floods. Let's look at what these are: •

Areal floods – these are floods occurring in low-lying areas after a strong rain or snowmelt. Depending on the mismatch between input of water and runoff, the amount of water can be significant. These are unassociated with any major body of water and come from an excess of water in an area that cannot handle it.

•

Riverine or channel floods – these are linked to rivers and streams. It can happen after snowmelt in the spring or from ice dams, beaver dams, or landslides.

Flooding can be gradual and rather predictable; others are rapid and unpredictable. Drier climates can have more rapid overflow after a strong rain.

Flash floods happen on smaller rivers and in those where the basins are impermeable to a great deal of water. A lot of this type of flooding depends on a combination of the amount of water in and the permeability of the banks and river basins.

•

Estuarine and coastal floods – this is flooding that happens in coastal regions after storm surges or tsunamis, accompanied by either high tides, low barometric pressures, and large waves in the ocean. The water moves inland and can rise severely to up to 20 feet or more above the flood stage.

•

Urban flooding – this is most common in densely populated areas when rain falls excessively, overcoming the ability of drainage systems to accommodate the excess water. There does not have to be any major river or floodplain nearby. You can get this type of flooding for obscure reasons as well, such as backed up sewers or broken pipes. Paved streets certainly worsen this problem.

•

Catastrophic flooding – this happens when something significant happens, such as a major dam breaking, an earthquake or a major landslide. Tsunamis can cause coastal flooding so catastrophic that many lives are lost.

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UNDERLYING CAUSES OF FLOODS You need to consider all factors that can contribute to flooding. Upslope factors are those that add water to the system. The main factors include natural precipitation and manmade issues, such as reservoir releases. Precipitation can evaporate or may percolate into the soil. There might be rapid runoff in rocky or paved areas or colder temperatures that lock the precipitation in frozen form. The ground may be frozen as well.

If the land upstream is a good watershed area, there will not be as much flooding.

Another factor is the intensity of the precipitation. The slope of the channel in a river or stream, for example, will also contribute to an increased intake of water into the system.

There are downslope factors to consider as well. These include anything that impedes outflow in a river or stream. In coastal areas, if natural bars form near the ocean during a flood, these will impede flow back into the seas, leading to flooding. Storm surges and tsunamis can reposition lakes near the shore or can create lakes that trap water in them.

Bridges or canyons can limit outflow of a river because of flow channel restriction. In reality, it is often a combination of factors that contribute to this problem.

FLOOD EFFECTS In general, floods are harmful. They can cause damage to property, infrastructure damage to bridges and roadways, and loss of life. Power lines and power generators can be damaged as well. Drinking water can be impacted and sewage disposal may be impeded. These issues can combine to increase the risk of many waterborne illnesses, such as cholera, typhoid, and giardia. Farmland can be so affected that crops won't grow or can't be planted. In some parts of the world, this can be extremely devastating.

The long-term effects of flooding are significant, including economic difficulties, food shortages, and psychological injuries. Damaged homes in urban areas can grow mold, which can affect the respiratory system and lower property values. Small business owners often lose business and close after floods. Damage to infrastructure can be significant as well and long-lasting.

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There are a few benefits of smaller floods. They can make the soil more fertile by recharging the groundwater and turning up the soil. In drier areas, floodwaters can bring in moisture that is badly needed. Floods can also improve the biodiversity in a floodplain area and can improve the fish population in a river or other body of water.

Birds and other animals can benefit.

FLOOD FORECASTING The goal in meteorology is to be able to forecast floods in advance. This can allow people to get out of the way and farmers to get their livestock to safety. The thing that helps the most is to have good historical data on past rainfall and flood events. When this is coupled with real-time information on grounds saturation levels and reservoir capacity, an accurate flood forecast can be gotten. You also need radar to help you estimate rainfall. There are statistical models you can use to help urban areas protect themselves against what is called a one hundred year flood. This is a flood that has a probability of about two thirds of occurring within one hundred years.

Around the world, people can use what is called the Global Flood Monitoring System, which is an online tool to help users determine if floods are likely in their area. The system uses satellites and precipitation data along with land surface models to help indicate the risk of flooding.

TORNADOES Tornadoes are violent storms you see as rotating column of air extending down from a cumulonimbus cloud to the ground during a thunderstorm. These create a windstorm that can cause serious damage to property as well as loss of life. Many have speeds of one hundred and ten miles per hour or less and are about eighty meters across. Most traveled just a few miles before dissipating entirely. Extreme tornadoes, however, can be much larger and more dangerous.

There are several rating scales for tornadoes that helps meteorologists describe their severity. The Fujita scale was the traditional scale used, although now a number of

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places in the world use an enhanced Fujita scale. Figure 39 shows the enhanced Fujita scale:

Figure 39.

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There is also a TORRO scale, which ranges from zero to 11, which is used in some parts of the world to assess tornado strength. These are assessed using photogrammetry, Doppler radar information, and ground swirl patterns after the fact. Together, these help assign severity levels and ratings to a given tornado.

Tornadoes do not have to be visible to the naked eye but they often are anyway. There are two reasons for this, including the development of debris in the tornado and the formation of water droplets. These droplets occur because of condensation occurring as the tornado cools. The rapid rotation will cause a significant negative pressure situation within them. The Bernoulli principle indicates why this low pressure develops inside the spinning vortex.

Funnel clouds are not necessarily tornadoes but most tornadoes are funnel clouds.

Funnel clouds are rotating clouds of any type. They do not necessarily mean there are strong winds linked with them. The term "condensation cloud" is a rotational cloud found below a cumulonimbus or cumulus cloud. Most tornadoes start as funnel clouds that do not have strong ground winds. Once these winds become evident, they are called tornadoes.

You may see tornadoes occurring as families or in outbreaks. One storm can have more than one tornado associated with it. These are called tornado families. If there is no break in tornado activities, you will call this a tornado outbreak. You call the situation a tornado outbreak sequence if several days in a row are linked to the development of tornadoes. These are also called extended tornado outbreaks.

TORNADO CHARACTERISTICS Most tornadoes have a characteristic funnel shape up to few hundred yards across. You may not see a tornado because of the dust or rain in the area. These become dangerous because they are so hidden. If there is some wind on the surface because of the vortex, it is called a tornado. You need surface winds of at least 40 miles per hour to call it a tornado.

There are several tornado sizes and shapes to consider. Short, cylindrical tornadoes are called stovepipe tornadoes, while wide, short tornadoes are known as wedge tornadoes.

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These can even be wider than they are tall, looking like a band of dark clouds rather than a funnel. Rope tornadoes are usually narrow, curly tornadoes that are dissipating. Their ropiness is what eventually dissipates their energy. Families of tornadoes can form with a common center.

Waterspouts are tornadoes that form over water. Those you see in good weather are not usually tornadic. They are a lot like dust devils on land with relatively weak wind and smoother walls. They do not move quickly and are usually seen in warmer waters, such as in Florida or other subtropical areas. There are tornadic waterspouts, however, that do have stronger winds. These are generally formed in bad weather and not in fair weather conditions. Most are not counted officially as tornadoes unless land is affected in some way.

Landspouts are also called dust tube tornadoes. These also form in fair weather rather than bad weather and are similar to waterspouts in many ways. The winds are weak and they do not last long. They actually have different basic mechanics than real tornadoes do.

A tornado's path width of damage can be as little as a few feet across or as wide as 2.5 miles. The record width so far is about 2.6 miles, while the record path length was 219 miles. Most longer paths are due to multiple tornadoes breaking out in a row.

LIFE CYCLE OF A TORNADO Tornadoes have a certain life cycle. They occur because of thunderstorms and usually from supercell thunderstorms. These thunderstorms contain mesocyclones, which are organized areas of rotation up in the atmosphere. The tornado life cycle begins as these mesocyclones. They lower from the base of the cloud, sucking cold and wet air leaving the cloud as a downdraft. The mixing of cold and warm air leads to rotation and low pressure formation. Low pressure sucks the mesocyclone downward toward the ground.

Tornadoes have a great deal of heat and moisture in the beginning; these things power a tornado and make it grow. Eventually, it fully matures, where it causes the most damage to the ground structures. The essential part of a tornado necessary for its endurance is

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its low pressure system. Eventually however, cooler winds wrap around the tornado that cannot get any of the heat it needs for power.

The tornado has no energy being added to it, so the vortex weakens and the tornado becomes a rope tornado. A rope tornado cannot sustain itself and it eventually dissipates completely. Rope tornadoes can still be damaging until they get so wrapped up and entangled that they dissipate. The mesocyclone weakens and there is no power coming down from the cloud either. On occasion, this does not happen completely and another tornado grows out of the same mesocyclone.

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KEY POINTS IN THIS CHAPTER •

Thunderstorms can have strong winds, heavy rains, and hail.

•

A thunderstorm will have certain cells, with a super cell thunderstorm having multiple cells.

•

Thunderstorms are what produce things like tornadoes, although most tornadoes come from super cells.

•

Flooding depends on how rapid water enters the system and how quickly it can be absorbed into the ground or fed into the ocean.

•

There can be upslope factors or downslope factors leading to the development of a flood.

•

Tornadoes come from mesocyclones and draw in moisture from the downdraft you see in a major thunderstorm.

•

A tornado is not considered a tornado unless it extends from the cloud to the ground and has winds in excess of forty miles per hour along the ground.

•

Tornadoes have a certain lifecycle in which they draw in energy in the form of heat and moisture. When this energy is cut off from them, they become ropey and lose their intensity, finally dissipating.

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CHAPTER TEN: QUESTIONS 1.

What phenomena is least likely to be associated with a thunderstorm? a. Strong winds b. Sleet c. Hail d. Fog

2.

What process happens first as a thunderstorm is developing? a. Ground or water surface radiation of heat b. Convection in the clouds c. Cumulus cloud formation d. Updrafts in the atmosphere

3.

The type of thunderstorm that spawns the most tornadoes is called what? a. Squall lines b. Multi-cell storms c. Single-cell storms d. Supercell storms

4.

What criterion does not go into calling a thunderstorm a severe thunderstorm? a. Hail greater than 1 inch in diameter b. Tornadoes c. Winds greater than 58 miles per hour d. Rainfall of greater than 2 inches per hour

5.

Which is a downslope contributor to flooding? a. Intense rainfall b. Poor drainage fields above the flooding area c. River debris d. Extreme slope of the river

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6.

What aspect of flooding will you least likely see as a primary adverse effect? a. Loss of infrastructure in a region b. Risk of disease in the community c. Crop losses d. Turbulence of soil

7.

What is the main difference between a funnel cloud and a tornado? a. A tornado has strong ground winds but funnel clouds do not b. A tornado is seen with thunderstorms but funnel clouds are not c. A tornado spins faster than a funnel cloud d. There is no difference between these two phenomena.

8.

You notice that a single thunderstorm has given rise to more than one tornado. What will you call this phenomenon? a. Tornado outbreak b. Extended tornado outbreak c. Tornado family d. Tornado outbreak sequence

9.

Which weather phenomenon indicates that a tornado is in the process of dissipating? a. A mesocyclone forms b. The tornado develops multiple vortices c. A rope tornado forms d. A land spout forms

10.

What aspect of a tornado most indicates its longevity on the ground? a. The surface air temperature at the base of the tornado b. The degree of low-pressure within a tornado c. The amount of moisture within the tornado d. The amount of surface winds you see in the tornado

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CHAPTER 11: HURRICANES AND OTHER TROPICAL WEATHER PHENOMENA This chapter delves into the topic of tropical weather phenomena, such as cyclones, tropical storms, and hurricanes. These can be powerful and damaging because of the heat that drives them coming up from the equator and other warm areas of the world.

We will talk about forecasting, naming, and tracking hurricanes as well as some of the more severe named hurricanes in North America. Tropical cyclones and how they evolve are discussed at the end of this chapter.

TROPICAL CYCLONES As you will soon learn, tropical cyclones go by many names. They are extremely destructive storms that develop in tropical areas above five degrees latitude, killing many people and destroying major sections of homes and other buildings, especially if severe. Their damage comes from the storm surge that comes onto land, rain, hail, and strong winds associated with these storms. Tornadoes can also pop up as result of these devastating storms. Coastal areas are particularly vulnerable to the destructive effects of these tropical storms.

The strong winds include squall lines, where the wind speed intensifies by any factor about 1.5 times and sustains itself for several minutes. This wind increase can be sudden and will cause severe damage if it happens on land.

Cyclones of this type can also spawn serious tornadoes, especially in the right upper quadrant of the storm if you look at it on the map. About half of all tropical cyclones will have these tornadoes associated with them. Rainfall and flooding are also very common with these types of cyclones.

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The storm surge itself can cause major coastal flooding. It is defined as a significant rise in ocean water ahead of the storm. It can cause riverine flooding and will flood low-lying areas, sometimes for a long time. It often affects hundreds of miles of coastline.

These storms get their energy from the heat and moisture given off by ocean water that has itself been heated by the sun. Water must be higher than 26 degrees Celsius or 78.8 degrees Fahrenheit to allow tropical cyclones to form. As they move over water, they gain energy but, as soon as they reach land, this energy does not come and the storm weakens.

PROPER TOOLS FOR A TROPICAL CYCLONE What do you need in order to have a proper tropical cyclone? Let's look at the necessary requirements: •

A large enough surface area on the ocean.

•

A surface temperature of greater than twenty-six degrees Celsius

•

Expansion of the atmosphere adiabatically with the surrounding air warmer in the periphery.

•

A location within five degrees of the equator at the time of the disturbance.

•

A pre-existing low level disturbance somewhere in ocean water that is warm.

•

Some type of vertical wind shear at the base or the storm first originates.

Remember that warm and moist air lifts. As this air lifts, it will circulate due to the Coriolis effect. The spin it generates creates the central low pressure system in a developing tropical depression. There will be centrifugal force involved as well, which will draw higher pressure outward, leaving lower pressure inward. As the spin intensifies, a hurricane is born. They get their energy or heat from the ocean and also because of condensation, which you already know generates heat.

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STAGES OF A CYCLONE'S LIFE SPAN There are four main stages that define the life of a tropical cyclone. These are the following: •

The formative stage – preexisting disturbances with shear lines allow an early cyclone to develop as mentioned above. They are not yet hurricanes at all.

•

The immature stage – the low pressure system deepens and wind velocity reaches its maximum. Some will die down during the stage, while others will intensify.

•

Mature stage – this involves expansion of the area of circulation. The low pressure system is at its maximum and the windspeeds have passed their maximum and will not intensify any further.

•

Decaying stage – this is also called the dissipating stage. The surface pressure increases in the cyclones size diminishes. There are three reasons why these diminish. These are friction, lack of moisture over land, and colder temperatures.

The most important thing to remember about tropical cyclones is how they get their energy. They begin by getting the energy from the ocean, which is warm near the equator. As this air rises rapidly, it begins to rotate and heat is generated by both convection and condensation of the water vapor. This upwelling of air and vertical mixing will decrease the ocean surface temperature at times, slowing the progress of the storm. This low-pressure system literally sucks water up from the ocean so that it is risen higher than it would be without the hurricane over it. This high ocean level is what creates the storm surge you see in hurricanes.

TROPICAL STORM TERMINOLOGY Tropical storms are all of the same type of weather phenomena but you'll see how they are named differently according to their characteristics and location. All are rotational storms linked to low pressure systems and severe winds, typical of other types of storms.

A cyclone is what a system like this is called in the South Pacific and Indian Ocean. The same system is called a hurricane in the Eastern Pacific and Western Atlantic Oceans.

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The people in the Western Pacific call these storms typhoons. The terms "hurricane" and "cyclone" are identical and both are tropical cyclones. Tropical cyclones are the beginning of these storms; these are spiral, low-pressure storms unassociated with any fronts. These gain strength from the fuel they get from tropical atmosphere.

Some of these ultimately become extratropical. You would use this term to describe a storm that as lost its tropicality by moving toward the poles and losing energy. Those that become extratropical get their energy from the contrast between warm and cold air and not from the heat of condensation. Any cyclone in the Northern Hemisphere east of the International Dateline and up to the Greenwich Meridian with winds of at least 74 miles per hour is a hurricane. Those west of the International dateline are called typhoons.

There are certain times of the year when the incidence of hurricanes is higher than others. Hurricane season depends on where you live. In the US along the Atlantic and Caribbean Sea, this season runs from June first through November 30th. In the Central Pacific, the season is also from June 1st through November 30th. In the Eastern Pacific, the season starts earlier on May 15th.

HURRICANE LIFE CYCLE Hurricane life cycles may last one day all the way up to one month in total length. No tropical cyclone has lasted longer than 31 days and a few have lasted as little as 12 hours.

Each of these start as an area of low pressure called a tropical disturbance. Surface winds come together as a depression, which is defined as a disturbance with circulation.

Once the winds reach 39 miles per hour, the depression is a tropical storm. As you know, it becomes a hurricane at 74 miles per hour.

TROPICAL DISTURBANCE (TROPICAL WAVE) Tropical disturbances are not terribly organized and appear like thunderstorms over water. They start off the west coast of Africa and move in an easterly direction toward the west along with the trade winds. Not all of these get much farther than this and dissipate on their own.

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Tropical depressions are more organized and have circulating winds. They do not look round like hurricanes but rather like grouped thunderstorms. There is defined low pressure in the middle but it is not particularly deep yet. Winds, however, are converging in the middle and energy is gained from the ocean itself. A storm is considered tropical because this is how it gets its energy and not from the atmosphere.

When this tropical transition occurs, the winds may or may not be above the 39 mile per hour threshold in terms of its maximum surface winds. You define this number by getting the maximum wind speed averaged over ten minutes of time in all parts of the world except for the US, where a one-minute average is gotten.

TROPICAL STORM You now know that a tropical storm has wind speeds between 39 and 73 miles per hour.

A few storms come directly from subtropical or extratropical cyclones rather than from tropical depressions. Once the storm becomes a tropical storm, it is given its name.

There are about a hundred of these cyclones created every year. Only half of these become mature typhoons or hurricanes.

HURRICANE AND ITS CLASSIFICATION Once a storm reaches the 74 mile per hour threshold, it becomes a hurricane or typhoon, severe cyclonic storm, tropical cyclone, or severe tropical cyclone, depending on where it is on earth. It will have a cloud-free eye easily seen. You would then use the SaffirSimpson Hurricane Wind Scale. You should memorize the different features for each hurricane category: •

Category 1 – winds of 74 to 95 miles per hour. Expect some damage to things like shutters and siding on structures and tree damage to branches or shallowly rooted trees. Power outages will be likely.

•

Category 2 – winds of 96 to 110 miles per hour. Expect damage to roofs, trees, and most power lines for weeks afterward.

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•

Category 3 – winds of 111-129 miles per hour. This is a major hurricane with much damage to homes and roof decks, trees, and power lines with power losses for many weeks afterward.

•

Category 4 – winds of 130-156 miles per hour. Expect catastrophic damage with wall and roof damage to homes, most trees lost, and downed power lines so that power outages could last up to many months.

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Category 5 – winds of 157 or more miles per hour. Expect catastrophic damage with most homes destroyed or collapsed. The area will be uninhabitable for up to several months.

With each category level, the risk of damage increases by fourfold. Even the mildest category one storms can cause significant damage, depending on where the hurricane lands and how fast it strikes. Damage comes from the storm surge, wind, hail, and rain.

Larger storms will have greater degrees of storm surging. More winds also mean a greater storm surge too.

TRACKING HURRICANES Hurricane models are used to track hurricanes. We now use supercomputers that get fed information and that also use historical records on prior hurricane behavior to determine the movement of a hurricane. In general, the longer a hurricane spends over water, the stronger it gets. Over land, however, and they lose strength, beginning to dissipate.

There are some things you want to track about a hurricane as you follow its progress over time. The path you predict will not be perfect but will be a "best guess" based on the information you receive from dynamical and statistical information. You would use these terms to describe a hurricane's behavior: •

Best track – this is your subjective best guess as to the hurricane's lifetime as indicated by where you expect it to be every six hours as it travels. It doesn’t reflect the fact that a storm can be erratic and unpredictable.

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•

Center – this is not the same as the eye but is the area where the air pressure and wind speeds are at their lowest levels. It will not be the same along a vertical axis so you would list its center where it exists on the earth's surface. You can get the center by using radar, satellite images, and reconnaissance aircraft entering the hurricane.

•

Central dense overcast – this is the thick cloud mass covering the eyewall of the cyclone.

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Direct hit – this is the when the hurricane hits at its maximum wind speeds upon land.

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Indirect hit – this is where the hurricane did not strike with a direct hit but still sustained high winds and tides that are at least four feet above what is normal.

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Eye – this is the area in the center with light winds and few clouds. The eye wall cloud is a ring of cumulonimbus clouds at the outer edge of the eye. This area can be called the eye wall or the wall cloud.

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Landfall – this is where the hurricane first reaches the coastline. It is not necessarily where the strongest winds will be and strong winds can still hit land when there is no true landfall.

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Maximum sustained surface winds – this is how we determine a hurricane's strength. As mentioned, it is averaged over 1 minute in the US and 10 minutes elsewhere at an elevation of 10 meters above the earth.

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Radius of maximum winds – this is often found along the inner edge of the eyewall; it is the distance from the storm's center to where its maximum winds are located.

NAMING HURRICANES Hurricanes are named in order to keep track of the many hurricanes that can be occurring at one time. The names can be used for others besides meteorologists so they can communicate with one another more clearly about the storms. Names are assigned

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in alphabetical order as they are discovered. Names may be repeated after six years unless they are retired permanently.

Atlantic names have been used for several hundred years. The Caribbean people named storms after the saint of the day in Roman Catholicism, but prior to that in the US, storms were named by their original longitude and latitude. This was cumbersome so names in the Pacific were given to storms originating after World War II. This plan was adopted in the US in 1953 for Atlantic storms. Men's names were added in 1979.

Twenty-one names are allotted every year in alphabetical order. Destructive hurricanes have their names retired. After 21 storms, the Greek alphabet is then used.

FAMOUS HURRICANES We've all heard about some of the worst hurricanes we've had in recent years, but you might be surprised that some of the worst storms happened beyond recent memory.

Let's look briefly at some of the worst hurricanes we've ever had in the US: •

Hurricane Camille – this hit the Mississippi gulf coast area in 1969 as a category 5 storm. It was the hurricane that resulted in the category ratings we use today. It would cost 21 billion dollars in damages if it occurred today.

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Hurricane Donna – this was a storm in 1960 in the Florida Keys area but remained a hurricane for a total of 17 days.

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Lake Okeechobee Hurricane – this happened in 1928, killing more than 4000 people in Florida because it destroyed a major dike on the lake.

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Cuba-Florida Hurricane – this happened in 1944 and killed 300 people in Cuba, damaging the Havana Harbor quite badly.

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The Great New England Hurricane – this happened in 1938 in Connecticut and Long Island at high tide. The storm surge was severe and killed up to 800 people, doing about $39 billion of today's dollars in damage at the time.

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Hurricane Andrew – this struck parts of Florida in 1992, being one of the more costly hurricanes we've had.

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•

1915 Galveston Hurricane – this killed nearly 8000 people in Texas, prompting officials to build a seawall in the area.

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1900 Galveston Hurricane – this is the worst natural disaster we've had in the US, killing as many as 12,000 people, destroying about 3600 homes and buildings.

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Hurricane Katrina – this struck Louisiana and Mississippi in 2005 and, while very destructive, it isn't the most destructive we've had. It killed more than 1800 people.

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The Great Miami Hurricane – this destroyed Miami as a category 4 storm in 1926 and would have cost more than $178 billion USD had it struck today. This is the costliest storm we've had in terms of dollars lost.

IMPORTANT POINTS IN THIS CHAPTER •

Tropical storms go by many different names depending on their intensity where they begin on earth.

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Almost all tropical storms originate within five degrees latitude of the equator.

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Most tropical storms move away from the equator region with the trade winds.

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Tropical storms must begin in an area where there is warm ocean water to draw energy from.

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Hurricanes are destructive for many reasons. There are storm surges, heavy rain, strong winds, and tornadoes to consider as damaging factors.

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Hurricanes are rated according to their windspeed.

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Up to 12,000 lives have been lost in a single hurricane event.

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Hurricanes lose their source of energy over land, which is why they dissipate soon after landfall in many cases.

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CHAPTER ELEVEN: QUESTIONS 1.

If you lived in the Western Atlantic area and had a severe low-pressure storm in the area, what would you most likely call this system? a. Typhoon b. Cyclone c. Tropical storm d. Hurricane

2.

What marker most predicts whether a tropical storm is a hurricane or typhoon? a. Greenwich meridian b. West Coast of US c. International Dateline d. East Coast of US

3.

In the lifespan of a hurricane, what defines the beginning, where there has not yet been any circulation of the low-pressure area? a. Tropical low b. Tropical disturbance c. Tropical depression d. Tropical storm

4.

What wind level will you look for, above which you would call a storm a tropical storm rather than a tropical depression? a. 21 miles per hour b. 30 miles per hour c. 39 miles per hour d. 48 miles per hour

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5.

Which category of hurricane indicates it is a major hurricane? a. Category 2 or more b. Category 3 or more c. Category 4 or more d. Category 5 only

6.

You are tracking a hurricane and decide it has become a category 5 hurricane.

What windspeeds will you look for to mark this kind of hurricane? a. Above 122 miles per hour b. Above 143 miles per hour c. Above 157 miles per hour d. Above 172 miles per hour

7.

How were hurricanes named in the Caribbean originally? a. By longitude and latitude of their origin b. Women's names only c. Men's and women's names d. Names of saints of the day

8.

Which hurricane in history was our costliest when factoring in today's estimated costs? a. Katrina b. Lake Okeechobee c. Great Miami Hurricane d. Galveston 1915 hurricane

9.

At what latitude do you most expect a tropical cyclone to have originated from? a. Directly at the equator b. At about five degrees latitude c. At about twenty degrees latitude d. At about forty degrees latitude

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10.

What condition is not necessary to build or create a tropical cyclone? a. Temperatures above the ocean at least 26 degrees Celsius b. A tropical disturbance over the ocean c. Large area of ocean d. Cold front over the ocean

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CHAPTER 12: OUR GLOBAL CLIMATE In this chapter, we talk about the global climate, including what it looks like now, what it might look like during climate extremes, natural climate change, and the effects on climate brought on by human activities. Climate and weather are not the same thing, but you will see how they are interconnected. There is a lot out there on global warming and predictions for our future; in this chapter we talk about what these predictions mean for the everyday weather in the coming years.

GLOBAL CLIMATE AND WEATHER As you know, the earth is large and constantly changing, with climates that are different throughout the planet. There are internal and external forces that participate in this ongoing change of scenery from place to place. From the beginning of our planet's existence, some of the internal changes have included magma coming up from deep inside the earth below the crust to create mountains and valleys. Some of these valleys have formed lakes or streams, while the vast areas between continents have become filled with oceans and seas. The sun has been ever present, continually participating in the weather and climate we have. Let's look at the different weather features that help to determine the climate from place to place on this planet.

As you know, the atmosphere circulates continually due to differential temperatures the different regions have. The sun's rays reach the earth differently, depending on where they hit. The earth also spins, adding to the Coriolis effect, which means we have an interesting pattern of circulation from the equator to the poles. There are also seasonal variations because of the tilt of the planet on its axis.

As you also know, there is a pattern or cycle of evaporation, condensation, and finally precipitation of the water on this planet. Water and air are both moved from the poles to the equator and vice versa. Remember that Hadley cells, the polar cells, and the Ferrell

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cells, which drive the winds throughout the planet. These have a huge effect on the precipitation patterns we see throughout our planet.

It is no accident that there are dry and warm areas at about thirty degrees north and thirty degrees south at the equator. This is because there is descending air in these areas that suck the moisture out of the soil. The trade winds happened in the subtropical areas because of the flow of warm tropical air and cool polar air over the oceans. This is just one example of how our atmosphere contributes greatly to our climate.

We haven't talked much about ocean currents, but these also affect the climate. Earth's rotation contributes to the flow of water in our oceans. Currents exist because of surface winds, differences in the salinity or salt content of the water in the oceans, and the rotation of the earth. The Western Pacific is far warmer than the Eastern Pacific by about 8 degrees Celsius. This is a huge temperature gradient that helps to form clouds and rain in parts of Africa, Indonesia, and Australia. You now know that this gradient can be disrupted in an El Nino year.

Colder water undergoes upwelling near land masses in South America, rising to the surface before becoming warmer. The line between cold and warm weather in the ocean is called the thermocline. Winds and cool water then rotate back toward the Western Pacific area.

The trade winds happen because of the earth's rotation, which then affect the surface temperature in the ocean, helping surface water flow near the equator from the east to the west in both great oceans. Water travels away from the equator in both directions and because of the Coriolis effect, rotation of currents happens in the oceans as well.

Currents tend to flow clockwise in the Northern Hemisphere and counter-clockwise in the Southern Hemisphere.

Frozen water in the north increases the salinity of these waters by removing pure water from the ocean liquid as ice. This leaves behind denser water that sinks. Water becomes densest also at 4 degrees Celsius. Now you may be able to see how this dense water drops to the ocean floor, travels southward, rises near the equator, and starts back up again in a large conveyor belt. Figure 40 shows this thermohaline conveyor belt:

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Figure 40.

The ocean currents are more complex than you would see just because of the thermohaline circulation. Figure 41 shows the currents you see because of each of the factors we talked about. Notice how the climate would be affected by these currents, especially near the oceans: This combination of currents and atmospheric changes help to determine what the climate pattern looks like. Climate involves a stable pattern of heat, moisture, and weather over a prolonged period of time. There are many climate forcing factors to consider, such as the effect of greenhouse gases, changes in solar radiation throughout the year, and manmade factors.

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Figure 41.

MILANKOVITCH CYCLES A Serbian mathematician developed a theory that helps explain changes in global climate based on several astronomical factors. He was Milutin Milankovitch and he developed a long-term strategy for why we have had ice ages, etcetera. His cycles are only part of the cycles we currently live with and that determine our climates all the time.

What he looked at were three variations in our orbit that affect the sunlight we get in the amount of warmth the sun gives us in any given year. Out of these variations he created what are called the Milankovitch cycles that can change the incoming energy we received particularly in the middle latitudes. These three variations are related to the following:

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1. The eccentricity of the earth's orbit.

2. The angle of the earth's tilt, called the obliquity.

3. The direction the earth's rotational axis is pointed, called precession.

Let's look at each one of these in turn.

You probably know that the earth rotates around the sun in an elliptical orbit. This orbit is not always the same ellipse. In fact, it changes slightly in a pattern that follows a one hundred thousand year cycle. The reason for the eccentricity of our orbit is that we occasionally come too close to Jupiter and Saturn, causing the earth to pull toward these planets and changing our elliptical orbit slightly.

The eccentricity of our orbit is why we do not have seasons of the same length. In the northern hemisphere summers are about 4.5 days longer than the winters and springs are three days longer than the autumns. When this eccentricity is less, the length of the seasons are more even. Overall, the difference in the length of the perihelion (where we are closest to the sun) and the aphelion (where we are furthest from the sun) is about 3.2 million miles. This is just 3.4 percent variation. Because we are closest to the sun on January 3, we get about 6.8 percent more sun rays than we do on July 4, when we are furthest from the sun.

Now, when we have our more elliptical orbits, we get almost 25 percent more of the sun's rays when we are close to the sun than we would when we are further from the sun. This would greatly affect the differences between summer and winter. Right now, the earth's orbit around the sun is quite circular so we would not see this pattern this is a cycle that spans nearly 100,000 years.

Next, we get to the changes in the tilt of the earth's axis relative to the orbital plane. The earth's axis is tilted, giving us our seasons. It turns out that this tilt ranges from 22.1 to 24.5 degrees. While this is slight, it can affect seasonal variations in our climate. The cycle created by this tilt change lasts forty-one thousand years. The greater the tilt of the axis, the more extreme the seasons will be.

Larger tilts mean that the glaciers will melt and retreat decreasing the chance of having an ice age. It makes sense then that smaller tilts would favor the development of an ice

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age. The further away you go from the equator, the greater the effect of the tilt will be.

Currently the earth's axis is 23.4 degrees. It is slowly decreasing, so that it will reach its minimum in about 9800 years. Theoretically, it would mean we would have warmer winters and cooler summers, favoring ice formation and cooling at the poles. Remember also that ice reflects the sun, so when we get more ice at the poles, the cooling effect is greater.

The final phenomenon affecting our climate in a cyclical fashion is called the axial precession. You can also call this a wobble of the earth's tilt. This cycle is approximately 28,000 years long. The wobbling is partly due to the tidal forces between the sun and the moon. These forces collectively make the earth bulge near the equator. It affects this phenomenon.

Axial precession tends to make the seasons more extreme in one of our hemispheres and less extreme in the other hemisphere. In our current time, our perihelion lies when we have winter in the northern hemisphere. What this means then is that the southern hemisphere will have more extremes and will have hotter summers, while the northern hemisphere does not have such extremes. This will change in about 13,000 years.

This wobbling our seasons so that they begin earlier over the course of time. Right now the two North stars are known as Polaris and Polaris australis. If you extended a line from the north pole out to the universe, it would run into the stars. Surprisingly, these were not are North stars a few thousand years ago.

Remember the effects of Jupiter and Saturn? These planets also affect the wobble of the earth on its axis. It makes the wobble slightly less predictable. This precession is called apsidal precession. The cycle of this is 112,000 years. When you combine the two types of precession, you get recessional cycles that are approximately 23,000 years, however, this is just an average.

When you put each of these cycles together and other cycles, you can see that there can be long fluctuations in our climate that have nothing to do with modern day activities.

Because these are cyclical, you can factor them in to past climate events and possible future climate events. Milankovitch was able to predict that ice ages occur every 41,000 years. This was only partially true and valid between one and 3 million years ago.

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Approximately 800,000 years ago, however, the ice ages became every 100,000 years.

This is probably due other cyclical changes we do not completely understand yet.

Milankovitch published his work in 1941; however, it was not taken seriously until years after his death. In 1976, deep-sea seven cores were obtained that proved his theories.

BIOGEOGRAPHY We can understand some of our climate differences by looking at the biodiversity of species of animals in the different regions or climates. During time periods long ago, when the earth was covered with a great deal of snow and ice, there was little livable land of plants and animals to thrive on. This made competition much more fierce. As the ice ages dissipated, you would not have seen as much competition among the species because they were more spread out.

You also need to remember that the continents themselves change over time. Some pushed together, while others spread further apart. There were areas where mountain ridges formed, and other areas where seas developed. Currently, there are about six different bio geographic areas on earth. They do not necessarily mean different climates altogether. These are called the Ethiopian, neotropical, palearctic, Australian, Nearctic, and Australian realms. The animals you find in these regions are distinct from one another.

CLIMATE EXTREMES You have probably heard of extremes in our climate, such as the ice ages. There are other types of extremes besides these. In terms of weather, there are many that affect our everyday life. Let's look at some of these.

DRY SPELLS AND DROUGHTS The term dry spell in meteorology essentially means a longer period without moisture than expected. When it begins to affect the climate in a serious way, we call it a drought.

A drought has no defined time period; it must simply be long enough to seriously affect

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water supply and cause crop damage from lack of water. In many parts of the world, this also means that food supplies are also short.

Droughts are variable in their intensity, with some being more severe than others.

Severity is dependent on how dry the environment is, how long it lasts, and how great an area is involved. You can define four different types of droughts. These are: •

Meteorological drought – you measure these by differences in the expected precipitation from the actual precipitation. It means that drought somewhere on earth might not be a drought elsewhere.

•

Agricultural drought – this is a drought when the amount of moisture the ground receives is not sufficient to support the normal crops grown in the area.

•

Hydrological drought – this is when there is insufficient amounts of water in the soil in a given area.

•

Socioeconomic drought – this involves any drought situation where the lives of the people in the area are affected.

Drought will affect everyone in a given area; in some parts of the world, a lack of rain can have devastating impact if even a few weeks of rain are missing from the weather pattern. In desert communities, however, long stretches of weeks without rain are not worrisome. It's only when many months go by that it is problematic.

These are the major effects on a community or part of the world affected by drought: •

Crop losses due to lack of adequate moisture

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Livestock losses, leading to food insecurity

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Disruption of transportation on major rivers, affecting commerce

•

Increased wildfires

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Diminished energy production from hydroelectric power sources and nuclear power sources

Dry winters are a particular problem because they affect snowmelt and drinking water for a region. One dry winter is usually okay, but more than one can have a serious

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impact on drinking water supplies. Fire dangers are more severe after dry winters.

Monsoon season and summer rain spells can help some of this problem.

The Dust Bowl time in the US in the 1930s was particularly severe with 50 million acres of land affected. Some difficulties were also had in the 1950s, when rainfall levels dropped in the Great Plains area. In both cases, crops were ruined and water supplies were greatly diminished. There were many cases since then where fires have broken out, causing forest fires and wildfires simply because of insufficient rain.

Drought can be predicted somewhat by monitoring precipitation, the flow of streams, and the amount of moisture in the soil. These together can predict when water deficits might be imminent in a certain area of the world.

WET SEASONS Wet seasons or "rainy seasons" are commonplace in many parts of the world. These are times when it is wetter for at least one month at a time. The tropical and subtropical areas are where you see these rainy seasons for the most part. Expect average precipitation to be more than 60 millimeters or about 2.4 inches. In some parts of the world, these seasons are in winter, while others are in summer. Interestingly, tropical rainforests don’t have rainy seasons as they have consistent rainfall.

While flooding can happen in wet seasons, they have the benefit of improving the amount of fresh, high-quality water, maximizing crop yields, and improving air quality.

Erosion worsens, however, and there will be worsened soil nutrients in some cases.

Higher levels of malaria and dengue fever are seen during wet seasons. If the winds shift in direction, we call these seasons monsoon seasons. The shift in winds goes from coming from the northeast to coming from the Southwest during monsoon seasons.

Rainfall in a wet season often happens in the afternoon and is due largely to the heating of the atmosphere by the sun. There will be thunderstorms and rain in an area where the airmass is already moist. There are periods of downpour, followed by a steady rain. One wet season is common in some parts of the world with two wet seasons in other parts.

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TEMPERATURE EXTREMES You can certainly have extremes in temperature with times of high heat and times of extremely low heat or what we call "cold snaps. Heat waves come when the heat index and surface temperatures are too high. The heat index factors and the humidity levels are used together when determining how uncomfortable and unhealthy the conditions will be.

We don't often think of heat waves as being extreme weather because we don't see them.

The truth is that they can be very severe and damaging to crops, humans, and the economy. Hyperthermia can kill many people who can’t protect themselves and who are physically vulnerable. Drier soils are more likely to erode and ruin the potential to grow crops in a certain area. Wildfires are more common during heat waves as well. Lakes and streams can dry up, killing marine wildlife. Livestock can be killed.

An interesting secondary effect occurs when plants essentially close up shop during a heat wave. In order to conserve water, they close their pores and quit many essential functions. This tends to increase the percentage of ozone in the air and the amount of pollution in the air. High pollution levels have been known to cause illness and deaths in humans. High electricity use is common in heat waves as well, so you can expect an increased risk of power outages.

Cold waves are also common in all parts of the world. A cold wave in the United States means that the temperature will drop over a short period of time, such as within a twenty-four hour period. This can be dangerous to industries, agriculture, and other parts of our economy. A cold wave is determined by the amount of temperature reduction and not by the absolute temperature.

Cold waves can happen anywhere, causing mostly death to wildlife and livestock.

Humans can die if they cannot find shelter. Animals need to take in more food when it is cold, so if food is unavailable because of ice and snow, this becomes hard to do. Farmers may not be able to support their livestock's food needs either. These are some things that make death from cold more likely.

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Cold waves occurring at the wrong time of the year can cause significant crop losses, which can affect humans a great deal. Famines can be associated with cold waves when food becomes unavailable. Frozen croplands have been linked to lack of crops and severe loss of food sources for an entire year.

PAST CLIMATE TRENDS While we have data collected for the past few hundred years, many scientists want to know what the weather and climate were like way before that – throughout the history of the world. In order to do this, researchers in the field of paleoclimatology aim to study the climate over millions of years ago. They use indirect measurements to get this information.

Tree ring data can often help determine what the climate was like in a certain part of the world. Each year, a tree grows its "annual ring". If this ring is wide, the year was favorable for growth. A narrow ring is less favorable. Glacier rocks also help determine climate. There are glacier rock patterns indicating where the leading edge of a glacier might be. Ice cores, ocean sediments, coral reefs, and fossils also help with early weather and climate information.

Another piece of data is collected when researchers drill holes into rocks inside the earth's crust. When taking temperatures of the rock at different levels, researchers can say a lot about what the Earth's crust was like at the different levels. Rocks do not change very much over time because of temperature changes. In addition, deeper rocks respond more slowly than shallower rocks to temperature variations. With this temperature information, researchers can determine the surface temperature of the earth at different times throughout the millennia. The idea behind all of this is to look for trends and cycles we can use to predict future climate change.

NATURAL CLIMATE CHANGE Our climate has always changed, even without human interference. Orbital changes, variations in solar energy output, ocean currents and volcanic activity have all contributed to climate change. Let's look at some of these:

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•

Volcanic activity – if volcanoes erupt in major ways, the entire globe will experience a cooling effect because of these eruptions. This is because of the clouds of ash and volcanic dust that block the sun's rays for months. Ash alone affects the climate for three months but, because it is heavy and falls to the ground, its effect does not last. Other volcanic output, such as sulfur dioxide gas, have a longer effect. This gas plus volcanic dust forms aerosols made of sulfur that will block the sunlight for more than a year. This greatly outweighs the warming effect that the greenhouse gases emitted from the same volcanoes.

•

Ocean currents – as we've mentioned, ocean currents are a major part of why we have different climates. All of our oceans are interconnected by a great current system, driven by winds, water density differences, and our earth's rotation.

Remember when we talked about the density of water, driven by its salinity, depth, and temperature. These are the issues that help to drive the oceanic conveyor belt; it's from this that you get a significant influence on the climates of the world. Just remember that warm water tends to flow toward the poles along the surface and cold water tends to flow towards the equator in the deeper part of the ocean.

•

Orbital changes – we have talked about these. The orbital eccentricities and rotational axis wobbles will set up specific cyclical changes in the pattern of our climate. These changes slowly affect the climate over tens of thousands of years.

•

Solar variations – the sun gives us all of our heat and energy. It actually has slight changes in its output over time; this can lead to major climate changes over time.

This is less predictable and less understood. It is believed that the Little Ice Ages in 1650 and again in 1850 were from changes in solar activity. This does not, however, seem to be a factor in our current global warming situation. Scientists know this because the sun's activities would affect all of the layers of the atmosphere at once, which is not currently seen.

•

Internal variability on our planet – these are changes we see unrelated to external factors. Examples include the Southern Oscillation, which you know already affects great parts of the world's climate in a cyclic fashion. There is also an Arctic

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Oscillation as part of the northern hemisphere. There are factors that bring warm weather to North America and some of Europe, taking it away from the Arctic.

This cycle is reversed in other years. It will influence the temperatures in a certain area but won't affect global weather greatly.

HUMAN-INFLUENCED CLIMATE CHANGES The effect humans have on the climate is called our anthropogenic influences on climate. We have a significant impact on ecosystems, the biophysical environment, natural resources, and biodiversity throughout the world. Our impact has led to global warming, loss of environmental resources, mass extinction of some species, crises in our ecological systems, acidification of our oceans, and loss of biodiversity overall.

There is much talk about how we have impacted or will continue to impact the environment and our climate. Let's look at the different factors related to anthropogenic influences on the earth and its inhabitants: •

Overconsumption – this involves our use of resources beyond the capacity of the earth to provide them. There are things we over-consume that cannot be easily replaced, such as petroleum products. Lifestyle issues and the overpopulation of parts of the earth both impact the problem of overconsumption. This is why we talk about reducing the carbon footprint. Carbon is the basis of petroleum products. We also overuse metals at too high a rate.

•

Overpopulation – human population growth has been significant in the past three hundred years compared to the millennia prior to this. So many people need to be fed and taken care of; this takes a toll on the world's resources. When we add the use of synthetic materials and items to be thrown away and not recycled to the problem, there is a big strain on the ecosystem. Resources are strained already and are expected to get more strained over time.

•

Farming and fishing issues – these involve poor agricultural practices that worsen the amount of emissions into the environment. Fishing will worsen the sustainable resources by overfishing or by damaging or destroying other species in the quest for getting the desired fish species. It is estimated that we will run 154

out of wild-caught fish in 2048 if nothing changes. The entire marine ecosystem is affected by these practices.

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Irrigation – this affects the ecosystem overall in direct and indirect ways. It can affect the water going through streams and rivers because it takes this water for irrigation instead. It will also affect the soil in ways that can be disruptive to the ecosystems of the world.

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Loss of land for agriculture – land has been lost due to degradation of the soil for many reasons. Soil can become too salty to be usable and erosion can damage cropland. Nutrients are lost, while other areas become too waterlogged or dry to use for crops. It is estimated that we’ve lost about 9 percent of our arable land since 1961 because of these issues. Others say that human activity has resulted in a 40 percent loss of usable land for crops.

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Meat production – you wouldn't think this is a big problem for the environment or our earth climate, but it can be. We get 18 percent of our calories from meat but use up 83 percent of our agricultural land to raise them; they also cause 58 percent of our greenhouse gas problem. Livestock involve 60 percent of the mammalian biomass on earth. Livestock raising causes use of fossil fuels, usage of land and water resources, greenhouse gas emission, and excessive use of our forests and rainforests. Ruminants themselves give off 27 percent of the methane released into the atmosphere. In reality, however, methane gas doesn't contribute to global warming as much as other factors. On the other hand, meat production uses up a great deal of water and feed, while polluting the water with manure in the water runoff.

•

Mass extinction of species – could humans be the cause of major species extinction? This seems to be true; it has been given a name – the Holocene extinction. This involves the extinction of species directly or indirectly as a result of human activities. We have hunted some species to extinction and have destroyed habitats or exhibited other activities that have caused the extinction rates to be 100 to 1000 times what would otherwise be normal. Many things we have done since the rise of mankind have contributed to such loss of biodiversity.

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What effects of these things do we see in the world's climate? We will talk about the major one in a minute, which is global warming. There are other effects we need to think about and work on in order to reduce our adverse impact on the environment. Global warming has been caused by overuse of petroleum fuels, carbon dioxide and other greenhouse gas emissions, disruption of the water resources, loss of the rainforests, and wasting the land to be used instead for livestock raising.

We have also contributed to environmental and climate changes by adding acid to our soil and water. This comes from the burning of fossil fuels, which return to earth as acid rain. We also disrupt the nitrogen cycle by producing too much nitrogen oxides in our industries and adding ammonia to the soil through fertilization practices. These can have long-term implications for our climate.

GLOBAL WARMING AND FUTURE EXPECTATIONS These are the main things humans have done to contribute to global warming: •

Increased the number of greenhouse gases in the atmosphere, adding a warming effect to the environment. Carbon dioxide is the greatest contributor to global warming as a greenhouse gas.

•

Deforestation and other land surface changes adding a warming effect.

•

Increased aerosols into the atmosphere, which could have a cooling effect.

Efforts have been made to predict the future of the earth and its weather as a result of warming temperatures. This is done by looking at what has been done so far to our climate and moving this forward several decades. Let's look at what these predictions indicate.

We have talked about what the different effects are of human activities on our climate, but there are other things we need to consider from the perspective of meteorology, such as whether or not there really has been an increase in extreme weather events. There has definitely been an increase in the incidence of hot summers in recent years. This might translate to an increase in extreme weather events overall. Expect stronger hurricanes and prolonged droughts.

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It is predicted that nearly the entire globe will be warmer than it is now by 2100 and that there will be more extreme heat events. The actual end result depends mainly on the number of fossil fuel sources we use. Even if we do a great deal, the temperature will increase by 1.8 degrees Fahrenheit and the sea level will rise by 17 inches. If we do not do anything, the global temperatures will increase by 7.4 degrees Fahrenheit and sea levels will rise by 29 inches.

Rain and snow predictions can also be made. Some areas will be rainier or snowier, while others will be drier. Storms in general will become more intense, leading to more erosion and flood conditions. Alaska and the Northeastern parts of the US will be wetter and so will areas near the equator. India, Canada, Northern China, and Russia will also be noticeably wetter. The countries in the Mediterranean and areas in Australia and Africa will be drier, on the other hand. The belief is that wet areas will be wetter and dry areas will be drier.

Sea level rise will occur all over the world but will impact different parts of the world in various ways. Areas near low-lying shorelines risk severe damage and loss of land as the ocean reclaims these areas. Other areas will have a loss of infrastructure, such as railways, highways, and sewage processing areas. The problem is that a warmer earth will melt the ice caps and glaciers, sending this water into the oceans of the world. A warmer ocean will also take up more physical space. Estimates vary but you might see up to 3 feet of extra seawater in coastal areas.

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KEY POINTS IN THIS CHAPTER •

Climate involves sustained changes in environmental and weather-related conditions in an area around the world.

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There are many factors affecting climate, including orbital factors, oceanic factors, internal factors, and human factors.

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There are cyclical changes in the climate predicted by aberrations in the earth's orbit.

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Natural factors affect the climate, such as volcanic eruptions.

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Humans change the climate through many behaviors ranging from livestock management to carbon emissions to our usage of the soil and water for our own purposes.

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Some global warming is going to keep occurring, even if we limit fossil fuel consumption.

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Weather extremes due to global warming include increased storm intensities, more droughts, and more heat waves.

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CHAPTER TWELVE: QUESTIONS 1.

What factor least affects the ocean currents? a. Salinity of the ocean b. Earth's rotation c. Precipitation patterns d. Surface winds

2.

According to the thermohaline conveyor belt, what causes water to mix in the way it does near the poles? a. The surface winds draw cold water away from the poles, churning up the water. b. The warm water from the equator rises near the poles from deep inside the ocean. c. Water doesn't mix much in the polar regions. d. Ice is formed, which increases the salinity and density of colder water, so it falls.

3.

What tends to happen when the earth's tilt is less pronounced? a. The equator's become very hot b. The poles become warmer c. The seasons become more extreme d. The earth gradually cools

4.

What makes the wobble of the earth somewhat less predictable? a. Gravitational pull from the gas giant planets b. Gravitational pull from the sun c. Tidal forces due to the effects of the sun and moon on earth d. Sun spots affecting the Earth's climate

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5.

What is not a positive effect of having a rainy season in a given area? a. Better water quality b. Reduced incidence of disease c. Improved crop yields d. Better air quality

6.

What defines a monsoon season rather than just a rainy season? a. The rains are more severe in a monsoon season. b. There are hurricanes in monsoon season. c. There is a marked shift in winds in monsoon season. d. There is no difference between a rainy season and a monsoon season.

7.

Which factor in the ocean does not directly drive the water density? a. Surface winds b. Temperature c. Salinity d. Depth

8.

When you study the global ocean currents, which trend do you see being accurate? a. Cold water toward the poles on the surface b. Cold water away from the poles on the surface c. Warm water away from the poles in the deeper waters d. Cold water away from the poles in the deeper waters

9.

Which greenhouse gas is most contributory to global warming right now? a. Methane gas b. Aerosols c. Sulfur dioxide d. Carbon dioxide

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10.

If we limit fossil fuel usage very quickly in the next few years, what is expected to happen to the temperatures and sea levels on earth by 2100? a. The temperatures and sea levels will both increase b. The temperature will increase but the sea levels will stay the same c. The temperature and sea levels will stay the same d. The temperatures and sea levels will both decrease

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CHAPTER 13: AIR POLLUTION This chapter covers air pollution as it applies to meteorology. There are many reasons for air pollution, not all of which are related to human activity. Air pollution has major consequences for human health; it is made worse by certain weather phenomena, like thermal inversions. There is a lot of talk about ozone and the ozone layer. This is a gas that also affects human health and our planet's weather and climate. As you'll see, urban areas are more affected by pollution than rural areas.

TYPES AND CAUSES OF AIR POLLUTION The kinds of air pollution that most affect our atmosphere and the air we breathe include the following:

PARTICULATE MATTER These can be anything from organic material, mineral dust, carbon particles, and any combination of solids and liquids. Smoke and soot are particulate matter. There are some of these that you can see by their larger size but so many more you can't see, called fine and ultrafine particles. These smaller particles are actually more dangerous than larger ones.

Particulate matter comes from building and industry, diesel engines, tire and brake friction, and road service dust. Natural sources of this matter can be sea spray, pollen from vegetation, volcanic activity, and soil/wind interactions. Gases can react in air to make solid particles.

The danger is mainly to lungs, because these particles get trapped in the airways, often leaching toxic chemicals into your bloodstream, getting directly into the bloodstream themselves, damaging lung tissue, and contributing to asthma. Other diseases like lung cancer are caused in part by particulate matter.

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NITROGEN DIOXIDE Nitrogen dioxide is a gaseous substance often causing urban air pollution. It mainly comes from heating units, power stations, and vehicles, especially diesel vehicles. You see it in peak levels along roadsides in particular. Nitrogen dioxide is inflammatory to your lungs and all the respiratory linings. It can cause a flareup of preexisting lung diseases, such as COPD and asthma. It may also trigger allergies, similar to those you see in allergic asthma.

OZONE Ozone is a gaseous substance made from three molecules of oxygen, as opposed to oxygen gas itself, which has two molecules of oxygen in it. It is emitted near the earth's surface when sunlight mixes with organic carbon-based gases and nitrogen dioxide emitted from a variety of sources, including automobiles, chemical plants, trucks, and power plants. Ozone levels will be greatest in warmer weather and in rural areas. It is seen most often in air pollution you find in summertime.

The lungs can be easily damaged from the inhalation of ozone. You will feel more short of breath from airway irritation and you might have asthma-like symptoms. People with lung disease have more problems inhaling ozone. Expect hospitalizations for lung diseases to increase when the ozone levels are highest.

SULFUR DIOXIDE This is also gaseous and smells like rotten eggs. It is made anytime you burn something with sulfur in it. This includes oil and coal products. All vehicles, heating sources, and power generators will produce sulfur dioxide as a byproduct of burning fuel. In most places, it comes from cement manufacturing companies and industries that burn petrol to make electricity. As it travels in the atmosphere, it helps to make ozone.

Sulfur dioxide can irritate all of the airway linings from the nose to the lungs. Some people will have worsening of their preexisting asthma or COPD. Those who have asthma are particularly sensitive to the inhalational effects of sulfur dioxide.

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SOURCES OF AIR POLLUTION IN THE ATMOSPHERE There are many sources of air pollution you need to consider if it is high in your area.

Remember that there is air pollution all over the world and that not all countries have enforceable laws related to reducing this health and environmental problem. The major sources of all types of air pollution include these: •

Burning fossil fuels – this is a major cause of air pollution in all parts of the world. Gasoline, coal, and oil are all fossil fuels used to make energy or to drive vehicles. Carbon monoxide in the air can be a good indicator of how much fossil fuel burning is going on.

•

Industries – we don't often see sooty black smoke from factories anymore but there are still emissions to worry about. Factories can emit particulate matter, carbon monoxide, sulfur dioxide, and nitrogen dioxide. Most of these use wood or coal as an energy source, with effects on the respiratory system and eyes.

•

Volatile organic compounds – these are called VOCs and are a major source of indoor air pollution. It often comes from the use of certain sprays and aerosols.

You will see VOCs in fragrances, cleaning products, and other personal care sprays. Their adverse effects are made worse by poor ventilation in homes, schools, and offices.

•

Wildfires – these are much worse due to the effects of air pollution; they are major contributors to air pollution throughout the world. Particulate matter is released along with toxic gases to affect air quality.

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Microbial decay – Bacteria and fungi both release gases, such as methane, as part of their metabolic processes. This is a large global issue because it's these bacteria that are found in the GI tracts of livestock, given off as intestinal gas.

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Transportation – vehicles of all sorts contribute to air pollution. It is more prevalent in urban areas. Areas of high traffic, such as urban areas, will be associated with more problems from this type of air pollution. Vehicles contribute to a hole in our ozone layer, contributing to smog and other health issues.

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•

Garbage waste burning – this is a problem mainly in parts of the world where this is how garbage is disposed of, such as India. About 9500 tons of waste in just one city in India is burned each day, causing major health problems for the people living there. Expect to see nervous system developmental impairment, cancers, liver disease, immune impairment, and disturbances in reproductive function from garbage burning.

•

Construction and/or demolition activities – this is true in all parts of the world where buildings are torn down and built up. Much of this gives rise to particulate matter and haziness from bricks and cement demolition.

•

Agriculture – this also decreases air quality, largely through the use of fertilizers and pesticides. Besides their damage to air quality, you will get mixing of these substances with groundwater, which also affects health of the community and region.

OZONE AND ITS EFFECTS Before we talk about ozone as a form of air pollution, we should talk a bit about the other aspects of ozone as it relates to our ozone layer around the earth. Human activities have led to depletion of this ozone layer, which largely protects us from excess UV ray exposure. This depletion does not cause global warming, however, as this is largely due to CO2 emissions.

Ozone absorbs UV radiation, while CO2 absorbs infrared or "heat" radiation, trapping it near our planet and preventing its cooling; it means that the earth's surface cannot release its stored energy as effectively. Ozone on the other hand is layered high above the earth but can easily be depleted by the halons and CFCs (chlorofluorocarbons) we release when we use refrigerants or utilize aerosol spray cans. The types of rays ozone collects and absorbs are those that can damage plants, animals, and humans.

As you can imagine, different molecules in the atmosphere have varying abilities to capture certain wavelengths of energy in the electromagnetic spectrum. Figure 42 shows this electromagnetic spectrum and where sunlight falls on this spectrum:

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Figure 42.

We will talk more about ground level ozone in a minute. The ozone in our atmosphere is considered "good" ozone because of its health benefits. As you know, this good ozone exists in the stratosphere around earth. The ozone hole in our atmosphere means that ozone is depleted there from the use of these CFCs and related airborne chemicals.

Without this ozone, we risk things like increased cataracts and sunburn-related skin cancer.

Ozone itself is made mostly knew the equator when sunlight interacts with oxygen molecules. When it is made, it flows naturally toward the poles and builds up in those locations. Cloudiness near the poles, however, tends to reduce the ozone that has concentrated there. CFC molecules become attached to ice particles near the poles. In the springtime, these CFCs are released and damage the ozone layer because most of their destructive power is in gaseous form.

In the early 1980s, researchers found that the ozone layer in the Antarctic area was becoming depleted. It was soon found that these CFCs, which contain chlorine or fluorine, were responsible for this depletion. One of the downsides is that these

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chemicals remain in the atmosphere for approximately one hundred years, although it depends on the type of CFC. Once it was determined that CFCs were a problem, the Montréal protocol was developed, which helped to reduce the numbers of CFCs we release into the atmosphere.

Because of this protocol, we no longer have aerosol spray cans but instead use aerosol pumps, which do not have CFCs in them. One problem, however, is that we may not be able to completely recover from the ozone losses we have already achieved.

Now, getting back to air pollution and ozone, you need to talk about ground-level ozone or what we call bad ozone. Ozone near the earth at its surface can be a strong irritant to the lungs. Children, elderly persons, and those with lung diseases are particularly susceptible to the effects of ozone near the ground. Ozone is the main chemical you will see in smog.

How to get all of this ozone? As mentioned, it is primarily caused by chemical reactions we see between two types of molecules. These are nitrogen oxides and VOCs or volatile organic compounds. In other words, when you mix emissions from cars, large boilers, power plants, chemical plants, and refineries, you will get ozone but only if it reacts with sunlight. Once made, ozone can travel for very long distances.

The effects of ozone are largely related to the lungs. It is a chemical irritant that can cause irritation of the respiratory passages, inflammation of the same, coughing, chest pain, and worsening of pre-existing lung diseases. High levels of ozone will also affect ecosystems of all types, particularly those with a lot of vegetation and wildlife.

ROLE OF WIND AND INVERSIONS ON AIR POLLUTION We have talked briefly about thermal or temperature inversions. Where they become more important is when talking about air pollution in urban areas. Let's first talk about these thermal inversions and why we get them. We need to understand this because air quality and our weather are tightly connected in many ways.

A temperature inversion involves the situation where cool air is trapped beneath warm air. You know by now that this is not it normally works. When this happens, the cool air

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has no place to go and it sits stagnant over an area on the earth's surface. Fog is actually a situation of a thermal inversion when it sits above the grass. It is humid air that is trapped along the earth's surface. Most thermal inversions will eventually disperse along with the wind or whenever the sun warms up the cool air above the inversion layer. The most common type of thermal inversion is called radiation inversion.

There are many reasons you can get a thermal inversion. Let's look at these: •

Ground Topography - if there are low-lying areas, such as valleys or ponds, cool air can settle into them below a layer of warm air. This will intensify any inversion you get.

•

Time factors – thermal inversions often occur in the evening hours. The surface begins to cool so it doesn't make it as much heat. Cool air begins to develop near the surface, largely because it cools faster than the air above it.

•

Seasonal factors – you will see inversions in the wintertime because the nighttime hours last longer. The land does not absorb as much heat so that the surface is cooler to begin with.

•

Wind factors – you need fairly strong winds to mix cool and warm air together. If the winds are fairly light, however, you have a tendency toward getting more thermal inversions.

•

Precipitation - rain also mixes layers of the atmosphere, which blocks the formation of a thermal inversion. Snow will also keep the land cool, worsening the inversion.

Thermal inversions tend to trap air pollution near the earth's surface. Under normal conditions, air pollution will travel away from an area because of the wind, rainy conditions, or natural dispersion into the higher atmosphere. If you see pollution gathering in a certain area that cannot escape to these mechanisms, it will build up further.

The three things that will determine how bad the pollution event is likely to be are these: the strength of the immersion, its duration, and the height of the area trapped beneath the inverted area. Certainly, the amount of pollution produced also plays a role. A strong

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inversion basically means there is a high thermal difference between the inversion layers and the mixing layers beneath it. If the inversion area is low to the ground, air pollution will be worse because there is a smaller volume in which to have the pollution collect.

When it comes to air pollution, there are four layers of the atmosphere to consider.

Closest to the ground is the smog area or the mixing layer. Above this is air that is cooler. Above this is what's called the inversion layer, which is the same thing as the warm temperature layer trapping the cooler area below it. Finally, there is the top layer we call the cold air layer. This is the normal cold air you would see in the higher atmosphere.

There are two types of smog that you can see in thermal inversion mixing layers. The first is a mixture of smoke and fog, which comes wherever factories burn coal. We call this industrial smog or London smog. We don't see much of this in developed countries anymore. The second type is called photochemical smog, seen mostly in Los Angeles, which gives it its name. This comes from automobile emissions and from power plants that burn fossil fuels. The smog is much different and contains other chemicals altogether. We will talk about the composition of smog in a minute.

London smog contains high amounts of sulfur dioxide. It was quite common in London during the beginning of the industrial age and cause a great many health problems throughout primarily the nineteenth century. The high amounts of sulfur dioxide come from the fact this is a major combustion byproduct of coal. When it mixes with air on foggy days, it creates a substance that is both acidic and corrosive and has added particulate matter within it.

Beginning in the early 1940s, people in Los Angeles started noticing a different type of smog that appeared like a yellow haze in the sky. It increased the risk of cancers and cause a great deal of respiratory irritation. We call this photochemical smog because it needs sunlight in order to develop. The components of this smog are the OCs, nitrogen oxides, ozone, and organic acids called PANs, which stands for peroxyacyl nitrates.

Is it possible to have a permanent inversion? Yes, there are relatively permanent inversions in the stratosphere between seven and thirty-one miles above the earth. The stratosphere essentially traps the troposphere layer and while it doesn't cause short-

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term pollution issues, it does impact our potential for long-term pollution around the globe.

URBAN AIR POLLUTION ISSUES Urban areas are particularly prone to air pollution. Many people in urban areas have some type of chronic health condition simply because of where they live. The biggest source of this type of air pollution is traffic. Particulate matter comes into important types. When we record particulate matter, we measure its diameter. The two types recorded are called PM 2.5 and PM10. Both of these are indicators of urban air quality.

PM2.5 is the smaller particulate matter. This small diameter particulate matter is more dangerous to our lungs than larger particulate matter. The sources of this particular matter varies greatly from place to place. In Beijing, for example, most is said to be coming from overseas, while the rest is due to vehicles, coal combustion, road dust, industries, and biomass burning.

PM 10, on the other hand, comes mainly from motor vehicles, with the rest coming from industrial processes, industrial boilers, power plants, and road construction or road dust. Other possible sources include construction and agricultural processes. In certain parts of the world, you might see particulate matter being caused by domestic fuel burning or by using coal for heating. In the Middle East and in areas of north Africa, PM 10 dust actually comes mostly from natural dust in the environment.

ACID RAIN Acid rain is essentially the deposition of acid onto the surface of the earth. Most of this will be sulfuric or nitric acid. They can be dry or wet when they fall to the earth, so the name acid rain is actually incorrect. You can have acid deposition through dust, hail, snow, rain, or even fog that happens to be acidic. Figure 43 shows the process by which we get acid rain:

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Figure 43.

In looking at this more carefully, you can see where these acid particles come from. They start out as nitrous oxide and sulfur dioxide released from emissions. They become transformed into acidic particles, where they can be transported far from the site they were first created. They combine with the elements just discussed to then fall to the earth. This then will cause the harmful effects we see on our soil, water supply, and vegetation.

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You can get these gaseous substances from volcanoes, but this is not common. It is more common to see them in industries that burn fossil fuels in order to generate electricity.

This is the most common source of acid rain. Vehicles like trucks and cars. Other industries, such as oil refineries and manufacturing companies, also add these emissions to the environment.

When we talk about wet deposition of acid, we usually mean acid rain. It can also mean other forms of precipitation. Dry deposition of acid usually means that the acid has attached to dust particles in the air. Because dry deposition can involve larger particles, these may be harmful to human health. Acid rain, on the other hand, mainly affects the health of insects, fish, vegetation, and smaller species of animals.

Normal rainwater has a pH of approximately 5.6. This means it is slightly acidic. The reason for this is that it has dissolved carbon dioxide in it and carbon dioxide itself is slightly acidic. Acid rain on the other hand has a pH between 4.2 and 4.4, which is more acidic. The amount of acid rain is measured in many parts of the world and is fairly easy to measure because it involves measuring the pH of rain and other precipitation. Dry deposition of acid, however, is more difficult because it is expensive to measure.

Nevertheless, we tried to measure all forms of acid on the surface of the earth because of its long-term impact on aquatic life throughout the world.

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KEY POINTS IN THIS CHAPTER •

Air pollution can involve particulate matter and a variety of gaseous substances.

•

Some air pollution comes from natural sources that cannot be controlled.

•

Much air pollution comes from emissions we see from cars, trucks, power plants, construction, garbage burning, and other industries.

•

The amount of air pollution on our planet varies greatly from place to place, with urban areas in developing countries and in places like India and China having the most air pollution.

•

Thermal or temperature inversions contribute to trapped air pollution that cannot be dispersed because of air trapping.

•

There is a big difference between London fog and Los Angeles fog, although both are hazardous to human health.

•

Small particulate matter is worse for your lungs than larger particulate matter.

•

Ozone helps to protect us when it is high in the stratosphere but when it is on the ground, it is a respiratory irritant.

•

Acid rain comes from many industrial processes; it can fall to the earth as wet or dry deposition of sulfuric acid or nitric acid.

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CHAPTER THIRTEEN: QUESTIONS 1.

What is not a health effect commonly due to air pollution that is mainly particulate matter? a. Cancer b. COPD c. Asthma d. Eczema

2.

You are checking the air quality in an area and find that there are high levels of nitrogen dioxide. What major source would you look for to see where this is coming from? a. Diesel trucks b. Clusters of homes and apartments c. Agricultural activities d. Volcanoes

3.

Which type of air pollution source most contributes to indoor air pollution? a. Motor vehicles b. Nearby industries c. Heating sources d. Volatile organic compounds

4.

Why do you find methane gas increasing because of livestock? a. The farms they reside on give off the gas in heating sources. b. The bacteria in the livestock's GI tracts give off this gas. c. The feed the livestock eat gives off this gas. d. The animals give off this gas as part of their metabolism.

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5.

What is not one of the three things you need in the recipe to make ozone on the ground? a. Sunlight b. Coal dust c. VOCs d. Nitrogen oxides

6.

What is not an ill effect from ground-level ozone? a. Damage to vegetation b. Increased risk of airway irritation c. Increased risk of sunburn d. Worsening of chronic lung diseases

7.

What is the main component of London smog but not of Los Angeles smog? a. Ozone b. VOCs c. Sulfur dioxide d. Nitrogen oxides

8.

What is not a major component of Los Angeles smog? a. Carbon dioxide b. Ozone c. VOCs d. Nitrogen dioxide

9.

What is not a major source of acid deposition on the earth surface? a. Wind b. Dust c. Snow d. Hail

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10.

What is the major source of acid rain in our environment? a. Volcanoes b. Manufacturing industries c. Transportation d. Fuel burning factories that make electricity

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CHAPTER 14: ATMOSPHERIC OPTICS AND HOW THEY AFFECT THE SKY This chapter will help you answer some of the more fun questions you might get asked as a student of meteorology. These involve the optical illusions and interesting aspects of the sky you see as the atmosphere interacts with sunlight and moonlight. There are many things to cover here, including why the sky is blue, why we have rainbows, and what the different types of moons and moon colors really mean. There are many other sun-related phenomena you may not understand yet that are covered in this chapter.

SKY COLOR AND ITS MEANING Under almost all conditions, the sky is blue to the naked eye. This is in spite of the fact that the color of light rays coming from the sun is white. What does this really mean that the sun color is white? There is no such thing as a white color in terms of light energy.

What white means is that it contains all of the colors of the rainbow at once. Sunlight is a collection of rays of the electromagnetic spectrum, which ranges from 750 nm - 400 nm in total wavelength.

Sunlight is a wave of charged particles that oscillate like any wave. Some waves are naturally longer than others. As these waves bounce from molecule to molecule in the atmosphere, they will be scattered all around the upper air levels. When you look more carefully at this spectrum, you will see that blue light has a shorter wavelength than red light. As these light energy waves come from the sun and get scattered, the blue light, being shorter in wavelength, gets scattered to a greater degree. In fact, it is scattered 10 times more significantly compared to red light.

This effect is called the Rayleigh scattering of light. When we look at the sky away from the sun itself, we see mostly light that has become scattered. This is why it appears blue.

Now, you might wonder why the sky isn't violet, because violet light is the shortest

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wavelength of light. The reason we see blue as the color of the sky and not violet, is because our eyes are not particularly sensitive to seeing the violet color.

At the horizon, however, we actually see some of the least scattered light coming from the dimming sun. We now see sunlight that is redder in color. As you go up from the horizon, you will see an increasingly bluish sky. Things that make the sunset so dramatic in coloration are pollution particles, which scatter lots of light to make a spectacular sunset.

Clouds have many water molecules in droplet form inside them. These droplets of water are large enough to scatter light differently. They scatter all light roughly the same so you will see a whitish coloration of light through clouds and no particular color as light passes through them.

Figure 42A

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The sun will emit the different colors of the visible spectrum roughly with the same intensity. Without this fact, our world will be rather dull in coloration. Sunlight that was more red would mean most things on earth would be red. Plants are green because they absorb reddish pigments to a greater degree, giving rise to green as the color they give off or scatter themselves. Figure 42A shows the light spectrum. You can expect that the color of an item will be the opposite to the color they absorb, and can determine this color by looking opposite to the color of the item: In actuality, the sun emits every wavelength of electromagnetic radiation waves, except for gamma rays. X-rays, UVA, UVB, radio waves, microwaves, and infrared waves are all waves emitted by the sun. It's the infrared rays that help us get warmth from the sun.

There are some peak energy frequencies in the color spectrum from the sun, but these are meaningless and do not show up in what we see or perceive from it.

The sun also has to has its rays travel through a greater slice of atmosphere during sunrise and sunset, largely because of the curvature of the earth. This means that blue light essentially gets scattered out of being able to pass much through the atmosphere, leaving behind mostly red light. The sunset on the moon would instead be white as there is no atmosphere to scatter the sun's rays.

MOON PHENOMENA AND THEIR MEANING Most people find the moon to be very interesting and will talk often about what phase the moon is in. For example, a full moon indicates that the moon is on the opposite side of the earth from the sun. You know of course that the moon has none of its own radiation so it does not give off light. It only reflects light from the sun. When we see the entire face of the moon with the earth in the moon and the sun, see this as a full moon.

When the moon is between the earth and the sun, there is no possible way you can see any light from the sun reflected off from its surface. This is called the new moon. Figure 43 shows the different moon phases:

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Figure 43A. What about some of the more unusual types of moon you have heard of? What is a blood Moon, for example? A blood moon is reddish in color, this is based on its color which is nearly the color of blood. This can only happen during a full or total lunar eclipse so that the moon is hidden completely behind the earth. You would not expect any light showing up on the moon surface. What you are seeing in a blood is the light that has reached essentially around the earth to reflect on the moon's surface. At this point, most of the blue light has been filtered out, leaving only red light from the periphery of the earth to reach the surface of the moon, reflecting off of it.

You may also call a moon a "blood moon" simply because it appears reddish in the sky.

The reddish color is seen because of smoke or haziness in the sky affecting the amount and quality of light we get from the moon. This situation is not a true blood moon.

A super moon exists when we see the moon quite large in the sky. Astronomically it means that the moon is closer to the earth than normal. Astronomers will call this a perigean full moon. This term means that the moon is at its closest point in its own elliptical orbit around our earth.

The term blue moon has several meanings. Most of the time it means that we are experiencing the 2nd full moon in a calendar month. Remember that calendar months are generally 30 to 31 days in total length and the moon has an orbit of just 29.5 days.

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This means that it is probable at some time to have 2 moons in a calendar month. It happens about once every 2.5 years.

A seasonal blue moon is actually much more rare. This describes a situation where there are 4 full moons in a single season. By season, we are referring to the astronomical seasons and not the calendar seasons. Still, there are 3 months in an astronomical season. If there are 4 full moons during that season, we call the 3rd moon the blue moon.

What is even more rare is the phenomenon of a seasonal blue moon and a blue moon in the same calendar year. This would mean 13 full moons per calendar year with one of them being a seasonal blue moon. The next time this is likely to happen is in the year 2048, when it will see a monthly blue moon on January 31 and a seasonal blue moon on August 23. Even weirder is the year 2067, when you will have a seasonal blue moon, a blue moon, and virtually no full moon in the month of February.

The term harvest Moon refers often to them only see during the autumn months when it is quite full and bright as it rises. It actually means very little right now but was important before we had electricity because farmers needed this bright light to continue their harvest.

WHAT IS GREEN FLASH? A Green flash is something you should try to look for some time. You only see it under favorable conditions at sunrise or at sunset. It depends on being able to see a mirage at that time and on the fact that sunlight disperses in specific ways when the sun is rising or setting. The Green flash is seen only a few seconds.

The mirage you see is not the same thing as a mirage you see on a hot roadway. Instead, it is an astronomical mirage, at least some of the time. There are actually 4 different mirages you can see.

•

An inferior mirage can be seen with the naked eye as the sun is dipping below the horizon. The mirage you see is identical to that you might see on the roadway.

•

A mock mirage is essentially caused by a thermal inversion in the atmosphere. It will look very similar to an inferior mirage.

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•

The sub duct mirage is interesting, because it shows the sun's image as an hourglass shape. The upper part of the hourglass will be green.

•

A Green Ray is very unusual and is a Green flash of light or beam of light you see shooting up from a Green flash. This is so rare that has not been photographed.

Figure 44 is a nice image of the sun setting and a Green flash.

Figure 44 If you want to see one yourself, the sky must be clear and you need an unobstructed view of the sunrise or sunset. These conditions usually mean the Green flash is best seen over water, although you may see it from an airplane, a mountaintop, or a very tall building, because you can see the distant horizon of these locations.

HALOS, SUNDOGS, AND SUN PILLARS There are several other interesting Sun -related phenomena you might see. Many of these are seen only on very cold days when there are lots of ice crystals in the sky. They 182

are caused by the refraction of light off of these ice crystals. Exactly what you see will depend on how far up into the atmosphere these ice crystals reach. It might also depend on the size and shape of these ice crystals. The term refraction means the bending of light. We will talk more about that later.

Most ice crystals are hexagonal shape, just like snowflakes only perhaps more boring.

When we see them in cold weather near the ground, we call them diamond dust. You need to know, however, that ice crystals are not always the same shape. Some can be more columnar in shape, while others are platelike. When we talk about refraction with ice crystals, there only 2 angles of refraction or bending to consider. These are 60 degrees or 90 degrees. The phenomenon you see depends on what angle light is being refracted.

Halos, on the other hand, can be 22 degree or 46 degree halos. These are called by different degree names based on the angle light is being refracted off of ice crystals. You may see them anytime of the year; however, the wintertime is best because of the cold weather and better conditions existing then for ice crystals to be present in the atmosphere.

Figure 45.

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A sun dog is seen as brightly glowing dots around the sun, because sunlight is refracting off of ice crystals that are plate shaped and seen in the cirrus clouds. You may see them anywhere in the world and you may see them associated with 22 degrees halos. You'll see sun dogs most commonly near sunrise or sunset. They may be reddish in color or bluish in color. Figure 45 shows these interesting sun dog spots: It is possible to see moon dogs as well. This involves light from the moon and is also refracted off of ice crystals. You often see these when the moon is full or nearly full.

We have already talked about light pillars, which are seen in Arctic regions as pillars of light emanating from any light source as a light is reflected off of plates of ice crystals.

You can also see light pillars associated with the sun or the moon. These are called solar light pillars and lunar light pillars, respectively.

RAINBOWS Everyone has seen a rainbow. They are beautiful sky phenomena often seen as a multicolored arc after a rainstorm. Light is reflecting off of water droplets after the rain, refracting in ways that spread out the white light into a specific color pattern. The angle of refraction is exactly 42 degrees so you only see the rainbow when you are looking at this angle from the raindrop. Rainbows are combination of reflection and refraction of light.

As sunlight strikes a raindrop, some of it is reflected back off of the raindrop. The rest of it enters the raindrop and gets reflected or bent. Light waves do not get bent at the same angle when they are refracted. The angle of refraction is based on the wavelength of light. This is why refracted light appears as a prism or rainbow of multiple colors.

The radius of any given rainbow depends on the refractive index of the water droplet.

Any droplet with a high refractive index or bending ability will produce a small radius of a rainbow. Saltwater has smaller rainbows than freshwater because its refractive index is greater. In reality, rainbows are full circles. You can see these full circles on an airplane but, because of the earth, you only see half of the circle from that vantage point.

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Remember the phrase "Roy G. Biv" which is a way to memorize the colors of the rainbow from red to violet. This will give you the colors of the rainbow in the correct order. You need to know that some researchers do not include the indigo color as this indicates a color too vague to tell the difference between it and blue. When you look at a rainbow, the red color will be on top and the violet color will be on the inner aspect of the arch. In general, the inside of a rainbow is brighter than the outside.

If by some chance light is reflected twice inside a raindrop, you will see a double rainbow. This is a secondary and more faint rainbow above a brighter one. You might notice that this rainbow is reversed. The secondary rainbow will be red on the inside and violet on the outside. It is possible to have more than 2 rainbows, although they are harder to see because of their faintness.

There are several rare rainbows you can see. A red rainbow is seen at sunrise or sunset.

You only see reddish colors because the blue and violet colors and become scattered by the thicker atmosphere. The fogbow can be seen when the droplets inside fog reflect and refract light in the same way you see in clouds. Some will have reddish colors and bluish colors only, while others may be white, mostly because these are very small droplets of water. A moonbow or lunar rainbow happens because of light that has become reflected off the moon first.

CLOUD IRIDESCENCE Cloud iridescence is very colorful and is an optical illusion you might see whenever a cloud is near the sun or the moon. They often look iridescent, similar to how you see soap bubbles on a watery surface. It is most commonly seen near altocumulus, cirrus, or cirrocumulus clouds. The reason you see this is because of the refraction of light from the ice crystals or water droplets in the cloud. You need to have fairly small and uniform crystals in order to see this phenomenon. It is best seen at the very edges of a cloud.

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KEY POINTS IN THIS CHAPTER •

The sky has many unique phenomena related to light coming from the sun.

•

The sun itself is white; however, it contains the entire spectrum of visible light, which allows for several unique things to be seen on earth.

•

The sky is blue because this is the light that most reaches our eyes when we see scattered light in the atmosphere.

•

Sunrise and sunset involved brighter colors of the sun because of the increased thickness of the atmosphere it must travel through.

•

The moon has many unique names for it, depending on the phenomenon. On occasion, you might see a blood moon, a super moon, or a blue moon. A blue moon is not truly blue in color.

•

There are number of cold weather phenomena related to ice crystals and their effect on sunlight. These include sun dogs, halos, and Sun pillars.

•

Rainbows are a combination of reflected and refracted light off of water droplets.

Remember the name Roy G. Biv to describe the different colors of the rainbow in order from the longest wavelength to the shortest wavelength of visible light.

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CHAPTER FOURTEEN: QUESTIONS 1.

What wavelength represents the white coloration we see from the sun? a. 440 nanometers b. 840 nanometers c. 220 to 335 nanometers d. 750 to 400 nanometers

2.

Which light on the visible spectrum carries the shortest wavelength? a. Blue b. Violet c. Red d. Orange

3.

What color is absorbed the most by a natural object that is red in color? a. Red b. Yellow c. Green d. Blue

4.

What emission from the sun is most responsible for the heat energy we receive? a. Infrared rays b. Gamma rays c. Microwaves d. Ultraviolet rays

5.

You are a meteorologist on the moon reporting on the sunset on this celestial object. What will you say to describe its color at sunset? It will be… a. Red b. Yellow c. Blue d. White 187

6.

You have just reported that the moon is full. When you next report the moon phase, which phase will you call it? a. Waxing gibbous b. Waning gibbous c. First quarter d. Waning crescent

7.

At what point in a calendar year might you see a blood moon? a. Only during the autumn b. Only during a full moon sitting low in the sky c. Only during a full lunar eclipse d. During any type of lunar eclipse

8.

If you were being literal by saying something happens once in a blue moon, about how often would you expect that occurrence to be? a. Every 6 months b. Every 2 ½ years c. Every 8.3 years d. Every 24 years

9.

Under what conditions will you least likely see a green flash at sunset? a. After a rainstorm b. On a very tall building c. Over water d. From an airplane

10.

You are looking at a rainbow. As you look at the different colors you follow them from red violet. What color will you see after yellow toward the violet end of the spectrum? a. Blue b. Indigo c. Orange d. Green 188

SUMMARY As you now know, meteorology is a complex but fascinating subject to learn about.

There have been some scientific principles you needed to know as basic skills; hopefully, however, these have been applied to more practical topics, like why we have rainbows, how tornadoes and blizzards develop, and why we need to worry about global warming.

The first chapter of the course talked about the earth's atmosphere, starting with what it once looked like and how it has evolved over time. We talked about what's in the atmosphere and the air we breathe in today's time as well as the different layers of the atmosphere from the earth's surface to outer space. We also discussed air pressure and air density as important baseline information you needed to understand meteorology. At the end of the chapter, you should have gotten an understanding of the physical space where our weather originates.

Chapter two looked at how the earth and our atmosphere are warmed and cooled. You learned how the sun plays a big role in how this planet stays warm but that there is more to it than that. We talked about how heat gets transferred in the atmosphere, why we have seasonal and other variations in temperature, what the solstices and equinoxes are all about, and what we mean by "the greenhouse effect". There is a great deal of talk about this effect on our planet, but, as you hopefully learned, it is not a new phenomenon and is not an altogether bad thing for a planet to have in moderation.

Finally, you understood the greenhouse gases and why they are called by this name.

In chapter three, you looked at the concept of temperature, including how to predict what a nighttime temperature will be. Diurnal variation is the temperature variation you see from night to day. This variation will depend on several factors, such as vegetation, cloud cover, and humidity. You also studied temperature variations on earth, which depend on altitude, latitude, and many local factors.

Chapter four in the course was essentially the study of hydrology or water in the environment. Besides the temperature, you usually want to know what if any

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precipitation there is outside. This chapter introduced the processes leading to precipitation. You learned what the different phase changes of water are called and what they look like in terms of the weather. After you studied this chapter, you should have gained a clearer understanding of why we have dew on the ground, foggy weather, and clouds in the sky.

In chapter 5, you learned about the subject of atmospheric instability and how this contributes to cloud formation and precipitation. In truth, the atmosphere is never completely stable but there are times where there are long stretches of weather without rain or even clouds. We also talked about how clouds form precipitation and how they form the type of precipitation you see that falls on the ground. There are many types of precipitation that range from rain to snow to everything in between.

Chapter six in the course was all about wind and wind patterns. You learned why we have wind in the first place and how wind can determine the weather. As you now know, wind instruments are used to measure wind speed and direction. Meteorologists can create surface maps you often see on television when the weatherman forecasts your weather. After studying wind and surface maps, you can now read these maps and make your own determination as to how windy you can expect a certain area will be.

In chapter seven, we dove deeper into the complex circulatory patterns seen in the atmosphere. You learned that there are several global patterns discussed in chapter six and many others you learned in this chapter that affect local and regional weather conditions all over the world. The oceans and large lakes exert their own effect on the earth's weather systems in numerous ways, which were covered in the chapter. By the end of the chapter, you should have been able to demonstrate how and why the atmosphere behaves as it does.

Chapter eight in the course brought you further toward being able to predict the weather. We talked earlier in chapters six and seven about things like air cell and convection cycles but not about large air masses that affect our weather patterns until this chapter. You learned about weather fronts from the perspective of the way air masses collide with one another. In some cases, these air masses lead to mid-latitude

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cyclones, which you now know are different from hurricanes and tornadoes. You were able to study these cyclones and how they form.

In chapter 9, we studied weather forecasting. In order to forecast the weather, you will need to have the proper weather tools. In this chapter, you looked at how meteorologists use tools to figure out the weather. You studied surface maps and how they can also be used to predict the weather. Finally, you learn the different terminology necessary to send out weather watches and warnings.

In chapter 10, you learned about thunderstorms, flooding, and tornadoes. You studied how thunderstorms form and why tornadoes often come from them. You learned how the Fugita or F scale works to describe tornadoes. You now understand why flooding can occur as well as the different types of flooding situations.

Chapter eleven in the course looked fairly deeply into the topic of tropical weather phenomena, such as cyclones, tropical storms, and hurricanes. You learned that these can be powerful and damaging because of the heat that drives them coming up from the equator and other warm areas of the world. We talked about forecasting, naming, and tracking hurricanes as well as some of the more severe named hurricanes in North America. Tropical cyclones and how they evolve were discussed at the end of the chapter.

In chapter twelve, we talked about the global climate, including what it has looked like in the past, what it looks like now, what it might look like during climate extremes, and the effects on climate brought on by human activities. You learned that while climate and weather are not the same thing, they are interconnected. In this chapter, we also talked about what climatologists have done to make predictions for the everyday weather in the coming years. The changes we expect are things you now know have a great deal to do with human activities.

Chapter thirteen in the course was a study of air pollution as it applies to meteorology.

There are many reasons for air pollution, not all of which are related to human activity.

You learned how air pollution causes major health hazards to humans and how it is made worse by certain weather phenomena, like thermal inversions. We also discussed ozone and the ozone layer. Ozone is a gas that also affects human health and our planet's

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weather and climate. As you learned too, urban areas are more affected by pollution than rural areas.

Chapter fourteen helped you answer some of the more fun questions you might get asked as a student of meteorology. These involved interesting things, like the optical illusions and fascinating aspects of the sky you see as the atmosphere interacts with sunlight and moonlight. There are many things you see in the sky that are covered in the chapter, including why the sky is blue, why we have rainbows, and what the different types of moons and moon colors really mean. There are many other sun-related phenomena you may not have understood before that you now know after reading this last chapter of the course.

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COURSE QUESTIONS AND ANSWERS 1.

What greenhouse gas was partly responsible for the earth remaining warm in its early days? a. Argon b. Oxygen c. Water vapor d. Methane

2.

What types of organisms were most responsible for the Carboniferous period on earth? a. Plants b. Bacteria c. Cyanobacteria d. Invertebrates

3.

What was the major feature of the Eocene epoch 65 million years ago? a. Major ice age b. Deposition of carbon into the swamps c. Warmer temperatures d. Expansion of invertebrates onto land

4.

Which is the approximate percent volume of nitrogen in dry air? a. 67 percent b. 78 percent c. 32 percent d. 21 percent

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5.

Which is the approximate percent volume of oxygen gas in dry air? a. 21 percent b. 39 percent c. 82 percent d. 91 percent

6.

Which atmospheric layer around the earth is the widest by far? a. Troposphere b. Exosphere c. Stratosphere d. Mesosphere

7.

Where will you see the ozone layer around the earth? a. Exosphere b. Stratosphere c. Troposphere d. Mesosphere

8.

Which layer of the stratosphere has nacreous clouds in it? a. Mesosphere b. Troposphere c. Thermosphere d. Stratosphere

9.

What prevents the experience of high heat in the thermosphere, even when the temps are markedly elevated? a. The air is too dense in this layer b. The air is not dense enough in this layer c. There is no atmosphere in this layer d. The sun's rays are absorbed by gas molecules in this layer

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10.

What layer is most responsible for the aurorae phenomena on earth? a. Exosphere b. Ionosphere c. Ozone layer d. Homosphere Answer: b. The ionosphere is made by the ionization of particles from solar radiation. This phenomenon creates the aurorae.

11.

Approximately how many miles is 1° longitude or latitude? a. 32 miles b. 120 miles c. 53 miles d. 69 miles

12.

Where is the prime Meridian located? a. India b. United States c. England d. China

13.

When measuring air pressure, what does not appreciably affect this value? a. Humidity b. Latitude c. Temperature d. Air pressure

14.

What factor does not affect the density of air? a. Volume b. Altitude c. Temperature d. Air pressure

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15.

Which situation involves radiation as a form of heat transfer? a. Home radiator b. Touching hot stove c. Plant grow lights d. Ice melting in a glass

16.

Under normal circumstances during the transfer of thermal energy, where does the thermal energy tend to travel? a. Bottom to the top of the system b. Top to the bottom of the system c. Spread out in either lateral direction in the system d. It varies a great deal from system to system

17.

Which statement about albedo is true? a. A higher albedo exists at the equator so more light is reflected there. b. A higher albedo exists at the equator so less light is reflected there. c. A higher albedo exists at the poles so more light is reflected there. d. A higher albedo exists at the poles so less light is reflected there.

18.

What percent of the heat absorbed by the equator gets transferred to the poles in order to balance heat on earth? a. 5 percent b. 20 percent c. 40 percent d. 80 percent

19.

What day would you most expect the rate of daylight hours to be decreasing the fastest? a. December 20th b. June 20th c. March 20th d. September 20th

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20.

What day is marked by the sun crossing high above the Tropic of Capricorn? a. December 20th b. June 20th c. March 20th d. September 20th

21.

Which rays gotten from the sun do you need to warn people about with respect to getting sunburn? a. UVA b. Microwaves c. Infrared waves d. Gamma waves

22.

Which greenhouse gas contributes most to heating the earth by absorbing more of the earth's energy? a. Carbon dioxide b. Methane c. Ozone d. Water vapor

23.

Which greenhouse gas comes from respiration of animals and decomposition of plant material? a. Methane b. Water vapor c. Ozone d. Carbon dioxide

24.

Which greenhouse gas is most increased by human activities since the industrial period? a. Water vapor b. CO2 c. Methane d. Ozone 197

25.

What scale for temperature is the standard international unit for temperature in scientific circles? a. Centigrade b. Fahrenheit c. Celsius d. Kelvin

26.

What aspect of the weather does a Stevenson screen not protect the thermometer inside them from? a. Wind b. Radiating heat from the ground c. Humidity d. Precipitation

27.

The atmosphere has different temperature readings from the surface of the earth to outer space. In which region of the atmosphere would you expect the temperature change to be the fastest? a. Troposphere b. Mesosphere c. Stratosphere d. Thermosphere

28.

You realize it's hot on your hike in the desert. Which temperature reading on your trusty thermometer would indicate you have just exceeded the world record for the highest temperature on earth? a. 35 degrees C b. 55 degrees C c. 64 degrees C d. 72 degrees C

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29.

What is not a downside of using a liquid in glass thermometer for large-scale temperature readings in meteorology? a. They are not very accurate b. They are fragile instruments c. They require a person to read them d. They respond slowly to changes in temperature

30.

Which thermometer or sensor would least be accurate in saying what the real air temperature is in your area? a. Liquid in water thermometer b. Radiometric thermometer c. Sonic thermometer d. Bimetallic thermometer

31.

Records of sea surface temperature have indicated an increase in this average number over the past century. What type of thermometer was use for this type of determination? a. Radiometric b. Sonic c. Bimetallic d. Platinum resistance thermometer

32.

What is one thing that a radiosonde will not measure? a. Temperature b. Humidity c. Wind speed d. Air pressure

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33.

When will you expect the highest daily temperature in your neighborhood to be? a. 10:00 AM b. 12:00 PM c. 2:00 PM d. 4:00 PM

34.

What factor least causes a reduction in the diurnal temperature variation in a given location? a. High humidity b. Cloudiness c. Higher elevations d. Shorter days

35.

According to the definition of climate, which does not determine the climate of a region? a. Amount of precipitation b. Length of the seasons c. Timing of precipitation d. Average temperature

36.

Knowing what you know about temperature and climate, what climate region would you say that most of Russia exists in? a. Polar b. Temperate c. Dry d. Continental

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37.

If you wanted to grow coconut trees in your backyard, which climate would be most appropriate for this? a. Tropical b. Continental c. Dry d. Temperate

38.

You are climbing a mountain and it is snowing out. You go up in elevation about 1000 meters. What decline in air temperature would you expect at the higher elevation? a. 1 degree Celsius b. 3 degrees Celsius c. 6 degrees Celsius d. 10 degrees Celsius

39.

Which process in the hydrologic cycle on earth does not involve a phase change in water? a. Snowmelt b. Percolation c. Evaporation d. Sublimation

40.

What 2 things account for the most transfer of water between the atmosphere and the ground on earth? a. Transpiration and condensation b. Evaporation and condensation c. Evaporation and precipitation d. Precipitation and sublimation

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41.

Where on earth will we find most of the existing water? a. In the groundwater b. Around the atmosphere c. In lakes, rivers and streams d. In the oceans

42.

Which phase change in water results in the greatest decrease in kinetic energy of the water during the phase change? a. Melting b. Freezing c. Evaporation d. Condensation

43.

Which phase change is most responsible for cooling the human body? a. Sublimation b. Evaporation c. Melting d. Deposition

44.

What factor will increase evaporation but decrease condensation rates? a. Dryer air b. Large surface area c. Windy conditions d. Cooler temperatures

45.

What factor would least support the formation of dew on the grass on any given morning? a. A dry, warm and sunny day the previous day b. Little or no winds at night c. A significant degree of cooling during the night d. A warm and muggy day the previous day

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46.

Under what condition would you least likely see the phenomenon of hoarfrost? a. Temperatures below 32 degrees b. Elevated humidity levels c. Sunny days in wintertime d. Fog in the morning

47.

What is not a condition that must be met to have fog? a. Light surface winds b. Conditions of high humidity c. The presence of condensation nuclei d. Warm temperatures

48.

What would least likely your source of condensation nuclei in a cloud? a. Pollen b. Air pollution c. Water droplet d. Dust

49.

Which type of cloud is not considered a low-level cloud? a. Stratus b. Stratocumulus c. Cumulonimbus d. Cirrus

50.

Cirrostratus and cirrocumulus clouds often signal what weather phenomenon? a. Cold front b. Warm front c. Tornado d. Snowstorm

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51.

Which cloud type is often called a tower cloud because they extend from low to higher parts of the atmosphere? a. Stratus b. Altostratus c. Cumulonimbus d. Cirrus

52.

Which type of cloud most signals good weather and might look like a bunny or special shape to you in the sky? a. Cirrus b. Altostratus c. Cumulonimbus d. Cumulus

53.

What characterizes an air parcel? a. The volume stays the same b. The temperature but not the pressure is the same throughout c. The temperature and pressure are the same throughout d. The volume of air must be a minimum of one kilometer cubed

54.

What is the dry adiabatic lapse rate of an air mass in meteorology? a. One degree Celsius per kilometer b. 10 degrees Celsius per kilometer c. 20 degrees Celsius per kilometer d. 30 degrees Celsius per kilometer

55.

What feature of an air parcel determines the level at which it sits in terms of vertical motion? a. Its temperature b. Its total mass c. Its total volume d. Its total density

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56.

You are going to undergo the process of sounding an area in your immediate environment. What device will you need for this process? a. An aircraft with a thermometer on it b. A temperature sensor about 2 meters off the ground c. A weather balloon and a radiosonde d. A satellite with a radiometric thermometer on it

57.

The Clausius-Clapeyron is a meteorological diagram that has an X,Y axis of what two factors? a. Temperature and percent saturation b. Temperature and dewpoint c. Pressure and temperature d. Lift rate and density

58.

What is the source of contrails in the sky? a. Thunderstorms b. Aircraft c. Satellites d. Sun spots

59.

By what process do you make a small cloud when you exhale on a cold day? a. You warm the air around you, causing a cloud. b. You mix warm and cold air together leading to condensation. c. You add moisture to air which saturates it, leading to clouds. d. You create a vortex with upward air movement and resulting adiabatic expansion of air.

60.

What would least likely contribute to an excess of cloud condensation nuclei in the atmosphere? a. Volcanic activity b. Forest fire c. Air pollution from a factory d. Recent rain 205

61.

Which type of aerosol is the most hygroscopic cloud condensation nucleus? a. Dust b. Carbon particle c. Sodium chloride d. Pollen

62.

Which type of cloud would you expect the largest raindrop to come from? a. Stratus b. Cumulonimbus. c. Cirrus d. Cumulus

63.

At what temperature must water be solid, unable to be a liquid supercooled article? a. -40 degrees Celsius b. Zero degrees Celsius c. -10 degrees Celsius d. -80 degrees Celsius

64.

Which type of ice crystallization forms in absence of a nucleus? a. Immersion freezing b. Contact freezing c. Deposition freezing d. Homogeneous freezing

65.

What is the cutoff size below which rain is called drizzle in inches diameter? a. 0.001 inch b. 0.02 inch c. 0.5 inch d. 0.25 inch

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66.

At what diameter would an ice pellet actually be called hail? a. 1/16 of an inch b. 1/8 of an inch c. One fourth of an inch d. One half inch

67.

Which type of precipitation most commonly is in the shape of a genuine ice crystal? a. Sleet b. Ice pellets c. Snow grains d. Snowflakes

68.

How often do you get data on rainfall using a tipping bucket rain gauge? a. Once per month b. Only when the attendant checks the bucket c. Every 15 minutes d. It depends on how fast the rain is falling

69.

Which type of the rain sensor actually measures the depth of the rain that falls? a. Tipping bucket b. Optical c. Doppler d. Impact

70.

Which type of rain sensor measures the speed of rainfall? a. Standard b. Optical c. Doppler d. Impact

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71.

Which stable air system is most responsible for very warm and dry regions around the earth? a. Equatorial low-pressure trough b. Sub polar low-pressure cells c. Subtropical high-pressure air d. Polar high-pressure cells

72.

What is the main reason why the air pressure tends to be less at the equator compared to the poles? a. The effects of gravity are greater at the poles that at the equator b. There are more mountainous regions at the equator compared to the poles c. There is more rain at the equator d. There is more moisture in the air at the poles

73.

Which is not a process causing air pressure differences on earth? a. Earth's gravity b. Air temperature c. Humidity d. Air composition

74.

You experienced advection processes in your neighborhood. When you do this, what are you experiencing? a. Precipitation b. Wind c. Sunny skies d. Warm air

75.

What land feature most promotes the development of katabatic winds? a. Large bodies of water b. High plateaus c. Very tall mountainous regions d. Glaciers

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76.

What is least likely needed to create Chinook winds? a. Warm moist air from a large body of water b. High mountains c. Desert d. Mountainous precipitation

77.

If you lived in an area with Santa Ana winds, what weather-related effect of these winds might you expect? a. Thunderstorms b. Hurricanes or typhoons c. Cooler days and nights d. Forest fires

78.

Which term does not fit with the others? a. Blizzard b. Haboob c. Dust devil d. Whirlwinds

79.

How many major convection cells exist on this planet? a. 2 b. 3 c. 4 d. 6

80.

The polar jet stream is found at the boundary between which two major cells in the Northern Hemisphere? a. Polar and Ferrell b. Polar and Hadley c. Hadley and Ferrell d. Hadley and the Equatorial doldrums

209

81.

What is the main cause of the Coriolis effect on earth? a. Jet streams b. Major oceans c. Earth's rotation d. The effect of gravity

82.

What is the difference between a trough and a ridge? a. A trough represents a section of low-pressure while a ridge represents a section of high-pressure. b. A trough represents a section of high-pressure while a ridge presents a section of low-pressure. c. Troughs are much wider than ridges d. Troughs indicate an area of good weather, while ridges indicate areas of poor weather.

83.

You see a weather map showing a blue line with blue triangles on it to your west. What will you likely expect in the near future in terms of the weather in your region? a. Rain or snow is expected b. Warm sunny days are expected c. High wind warnings should be released d. Warm rain is expected, followed by a high-pressure area and nice weather

84.

You have just purchased a brand-new handheld anemometer. What will you now be able to do? a. Tell the temperature in your area b. Predict wind speed and direction in your area c. Predict the onset of a cold front d. Predict the angle of the sun at any given point in time

210

85.

At which latitude will you find the greatest heat deficit happening when you factor in the input of the sun's rays and the output of IR energy from the earth's surface? a. 0 degrees b. 30 degrees c. 60 degrees d. 90 degrees

86.

If we only had one cell around the globe from the equator to the poles, where would our surface level winds mainly come from? a. South b. North c. East d. West

87.

What type of weather phenomena would you least expect to see in the doldrums? a. Clear and sunny skies b. Thunderstorms c. High humidity d. Light winds

88.

Where in the world will you see a semipermanent high? a. Over Hawaii b. Over the Aleutian Islands c. Over Nevada d. Over Iceland

89.

Where in the world would you most likely see a semipermanent trough? a. Over England b. Over upper Africa c. Along the equator d. Over the North Pole 211

90.

Which of these local wind patterns is seen almost exclusively at night? a. Land breezes and katabatic breezes b. Land breezes and anabatic breezes c. Sea breezes will and katabatic breezes d. Sea breezes and anabatic breezes

91.

What is not a requirement for the development of wind shear or clear-air turbulence from mountains? a. Isolated mountain b. Temperature inversion at top of mountain c. Maintenance of wind direction at the different altitudes d. Strong winds perpendicular to the mountain range

92.

Which action by an airline pilot will least likely cause turbulence to be experienced on the plane? a. Flying near the tropopause b. Leaving the jet stream c. Flying at constant altitude d. Suddenly changing course

93.

What is the main cause of an eddy in the atmosphere? a. A strong thunderstorm b. A high mountain ridge c. A large expanse of cold ocean d. Winds that approach rough terrain

94.

Where do you see the origin of hurricanes to be? a. In the mid-Atlantic area b. In the mid-Pacific area c. At the equatorial low-pressure area d. In the Gulf of Mexico

212

95.

What factor least effects the natural cooling of the Eastern Pacific Ocean compared to the Western Pacific? a. Trade winds b. Natural tilt of the earth c. Water coming northward from southern regions of South America d. Ocean upwelling in Peru

96.

What type of air is transported from Peru to Australia in the Walker cycle phenomenon? a. Warm and dry air b. Warm and wet air c. Cool and dry air d. Cool and wet air

97.

What has been the effect of global warming on the southern oscillation? a. There has been an increase in El Niño years and in El Niño intensities b. There has been increased and La Niña years and intensities. c. There has been an increase in El Niño years but a decrease in their intensities d. There has been no change the frequency of El Niño years and no change in their intensity

98.

What will you not see in a La Niña year? a. Strong trade winds b. Storms in the western Pacific c. Good fishing along the coastline of Peru and Ecuador d. A greater chance of blizzards in the Midwest

213

99.

How would you label an air mass that comes down from a source region in the area on the north pole? a. MT b. CA c. MP d. CT

100.

What is not an attribute you would ascribe to an air mass? a. Cold b. Warm c. Moist d. Windy

101.

From where does the air in the eastern side of the dryline in the US come? a. Pacific Ocean b. Polar regions c. Atlantic Ocean d. Gulf of Mexico

102.

About how long will an air mass need to sit in a source region to be able to acquire and maintain its characteristics? a. 12 hours b. 3 days c. 7 days d. 1 month

103.

Which characteristics would you expect an airmass developing over Canada to take on? a. Warm and dry b. Warm and wet c. Cold and dry d. Cold and wet

214

104.

How would you most likely name an air mass coming from the Indian Ocean? a. cE b. mP c. mA d. mE

105.

Which type of front will most likely give extremely bad weather as they pass through? a. Occluded fronts b. Stationary fronts c. Warm fronts d. Cold fronts

106.

In what way or ways do mid-latitude cyclones differ from hurricanes? a. These cyclones are smaller than hurricanes in the same general vicinity b. These cyclones are larger but in the same general vicinity c. These cyclones are larger and further north than hurricanes d. They are not at all different but have different naming conventions

107.

When looking at a mid-latitude cyclone, which pattern will you see? a. High-pressure air in the center with the cyclone rotating clockwise b. High-pressure air in the center with the cyclone rotating counterclockwise c. Low-pressure air in the center with the cyclone rotating clockwise d. Low-pressure air in the center with the cyclone rotating counterclockwise

108.

Which known type of North American mid-latitude cyclone is the most intense? a. Colorado Lows b. Nor'easters c. Alberta Clippers d. Gulf Lows

215

109.

Which known type of North American mid-latitude cyclone is considered the least intense? a. Colorado Lows b. Nor'easters c. Alberta Clippers d. Gulf Lows

110.

How often do geostationary satellites capture an image of the earth? a. Every thirty seconds b. Seven times a day c. Twice a day d. Every forty-eight hours

111.

In what way do polar satellites move? a. They move in a circle around the top or bottom of the earth b. They travel north to south and back again from pole to pole c. They travel in a spiral around the earth from the equator to each pole d. They generally do not move but keep up with the earth's rotation so as to always capture the weather at the poles

112.

What type of image can you likely get from a polar satellite but not a geostationary satellite? a. Volcanic activity b. Mudslides c. Hurricanes d. Forest fires

113.

What type of information will you not get from an automatic surface observing station in the United States? a. Sunrise and sunset b. Surface temperature c. Sky conditions d. Rainfall amounts 216

114.

If we use the Global Data Assimilation System, how far in advance can we make a weather prediction? a. Five days b. Ten days c. Sixteen days d. Six weeks

115.

How far in advance can the Climate Forecast System Predict what the weather will be in your region? a. One month b. Three months c. Nine months d. Three years

116.

What system would you use if you wanted to get an hour by hour assessment of the weather in your region up to eighteen hours in advance? a. Rapid refresh b. Climate forecast system c. North American mesoscale d. Global forecast system

117.

You are an aviator looking at a weather depiction chart. What will you not easily be able to see on these charts? a. Isobars b. Areas of snow or ice c. Temperature d. Cold and warm fronts

217

118.

You are flying out in your light plane and get a weather prognostic chart to help you. How far ahead can you get this map to accurately know the weather for your trip? a. 8 hours b. 24 hours c. 48 hours d. 5 days

119.

Damaging straight line winds in a storm system are also called what? a. Cyclonic winds b. Tornadic winds c. Downdrafts d. Downbursts

120.

Where will you see a hook echo within a storm, indicating a probable tornado? a. Southwest b. East c. Northeast d. Northwest

121.

Which aspect of a thunderstorm will you least be able to physically see outdoors? a. Rain-free base b. Hook echo c. Mammatus d. Precipitation shaft

218

122.

Which type of cloud is a low-lying clouds with ragged edges seen on the backside of a thunderstorm system? a. Shelf cloud b. Roll cloud c. Scud cloud d. Mammatus cloud

123.

What will not usually be a cause of coastal flooding? a. Storm surge b. High offshore winds c. High tidal regions d. Sea breezes

124.

What is the adequate definition for heavy snow? a. One fourth inch per hour b. Six inches in twenty-four hours c. One inch per hour d. It depends on where you live

125.

Which winter weather watch or warning is no longer in use? a. Winter weather advisory b. Blizzard warning c. Heavy snow warning d. Ice storm warning

126.

If a warning is in place for winter weather, when should you expect the weather to arrive? a. In approximately three days b. It is probably imminent or happening within forty-eight hours c. You can expect it about forty-eight hours from now d. It is already occurring

219

127.

Which emergency situation would indicate the greatest potential for loss of life? a. Tornado emergency b. Tornado warning c. Tornado watch d. Particularly dangerous tornado warning

128.

You have issued a severe thunderstorm warning for your area. How long is that warning in effect? a. Fifteen minutes b. Up to one hour c. Up to four hours d. Up to eight hours

129.

You have decided to issue a severe thunderstorm warning. If winds are involved, what is the cutoff point you would indicate as the lower limit to be able to call it a severe thunderstorm warning versus a severe weather advisory? a. Twenty-six miles per hour b. Thirty-two miles per hour c. Fifty-eight miles per hour d. Eighty-two miles per hour

130.

You have indicated that a flash flood warning is occurring in your area. What situation is least likely to cause this flash flood? a. A dam has burst b. There has been significant rainfall within the last six hours c. There is an ice jam in a local river d. The snow has been melting over the past two weeks

220

131.

You have decided to issue an areal flood watch. What type of area is not included in this type of flooding situation? a. Storm drains b. Streets c. Coastlines d. Streams

132.

Which coastal flooding watch for warning is strictly limited to hurricanes or tropical cyclones? a. Coastal flood watch b. Coastal flood warning c. Coastal flood advisory d. Storm surge warning

133.

There is a red tide with algae growing in the waters along the shoreline where people swim. Recognizing the danger of this, what would you issue to protect people? a. Marine hazard advisory b. Beach hazard statement c. Rip current statement d. Beach warning

134.

Which type of extreme weather condition is only issued in Alaska? a. Extreme cold warning b. Freeze warning c. Hard freeze warning d. Windchill warning

221

135.

At what temperature or below which you indicate for farmers that a hard freeze warning is necessary? a. Thirty-six degrees Fahrenheit b. Thirty-two degrees Fahrenheit c. Twenty-eight degrees Fahrenheit d. Twenty-one degrees Fahrenheit

136.

Which type of weather advisory is generally not associated with the growing season of crops? a. Frost advisory b. Freeze warning c. Hard freeze watch d. Wind chill advisory

137.

What signals the start of the dissipation of a thunderstorm? a. Strong winds within the cloud b. Downdrafts exceed the updrafts c. The cloud becomes too warm d. Rainbows form

138.

What causes the downdrafts within a thundercloud? a. The condensation of droplets give off warm air that rises to create these downdrafts b. Gravity causes the warm air to fall c. Raindrops get heavier, making the air around them denser d. The air gets colder and drops downward with raindrops in it

139.

You are reporting on a single cell thunderstorm. By definition, a cell in a thunderstorm refers to what? a. A certain square footage of area covered by a storm. b. A cloud height of less than 10 miles in total depth. c. The number of updrafts in the storm. d. The volume of the thundercloud in total.

222

140.

What will you most commonly associate with a bow echo within a thunderstorm? a. Straight line winds b. Thunder and lightning c. Hail d. Thunderstorm dissipation

141.

What will you least likely see as a result of a mesoscale convective system? a. Polar lows b. Lake effect snows c. Blizzards d. Squall lines

142.

What is not likely to be a cause of a flash flood near a river? a. Snowmelt in spring b. Downstream dam c. Thunderstorm d. Rocky riverbeds

143.

What is not a major reason for coastal flooding? a. Global warming b. Tsunamis c. Hurricanes d. Snowmelt

144.

You heard about an area where catastrophic flooding has happened. What is most likely to be the cause of this? a. Snowmelt b. Tsunami c. Thunderstorm d. High tides

223

145.

What is most necessary to have in order to best predict flooding in a given area? a. Historical records on past floods b. Computer models of rainfall projections c. Climatology information d. Weather station information

146.

In the enhanced Fujita scale measurement of tornado severity, what number represents the most severe tornadic activity? a. Zero b. Three c. Five d. Ten

147.

What is not used to provide a rating to a given tornado? a. Doppler radar b. Eyewitness accounts c. Ground swirl patterns d. Photogrammetry

148.

What factor is necessary to call something a tornado? a. It must cause some degree of ground damage b. It must have rotating winds in excess of 110 miles per hour c. It must rotate counterclockwise. d. It must extend from cloud to ground

149.

What is the surface wind requirement you need to call a funnel cloud a tornado? a. 20 miles per hour b. 40 miles per hour c. 60 miles per hour d. 80 miles per hour

224

150.

What type of waterspout would you designate as an actual tornado in official statistical records? a. If winds are greater than 40 miles per hour at the base b. If they form in bad weather c. If they form in lakes but not oceans d. If land is affected in some way

151.

From what phenomenon do most tornadoes come as they are starting to develop? a. Mesocyclones b. Waterspouts c. Dust devils d. Polar vortexes

152.

You would call a tropical storm a hurricane if the sustained winds were greater than what? a. 54 miles per hour b. 74 miles per hour c. 88 miles per hour d. 94 miles per hour

153.

If you live in a hurricane prone area, when would you consider hurricane season to be over? a. November 30th b. November first c. December 31st d.

January 31st

225

154.

If you live in Miami, when would you begin to expect hurricanes as it indicates the start of hurricane season? a. April 1st b. May 1st c. June 1st d. July 1st

155.

What is the maximum time a hurricane has been declared a hurricane? a. 4 days b. 10 days c. 21 days d. 31 days

156.

Where should you look for the origin of the hurricanes that come to the US? a. West coast of Africa b. East coast of South America c. Caribbean Sea d. Western Europe

157.

What defines a storm as being tropical versus not tropical? a. A tropical storm will be more circular in nature b. A tropical storm will have stronger winds c. A tropical storm will have warmer temperatures d. A tropical storm will get its energy from the ocean

158.

About how many hurricanes or typhoons do we get in the world each year? a. 15 b. 25 c. 50 d. 100

226

159.

When in the life cycle of a tropical storm do we finally name it? a. When it is a tropical depression b. When it is an extratropical cyclone c. When it is a hurricane d. When it is a tropical storm

160.

Which category of hurricane does not produce any significant damage? a. Category 1 b. Category 1 and 2 c. Category 1 through 3 d. None of these

161.

How many more times damaging will a category 3 hurricane be compared to a category 1 hurricane in general? a. Twice as damaging b. 4 times as damaging c. 8 times as damaging d. 16 times as damaging

162.

What do you call the cumulonimbus clouds nearest the center of the hurricane? a. Eyewall b. Eye c. Strike zone d. Storm surge

163.

At what height do we measure the winds in a hurricane to determine its intensity? a. On the ground b. 10 meters above the ground c. 500 meters above the ground d. 1000 meters above the ground

227

164.

Which hurricane year was our deadliest year in the US? a. 1900 b. 2005 c. 1915 d. 1938

165.

What is least likely to contribute to loss of life and property damage in a tropical cyclone? a. Tornadoes b. Lightning c. Storm surge d. Winds

166.

If you are in an area where a hurricane has a squall line, what would you expect to experience? a. Storm surge b. Hail deposition c. Sudden increase in wind d. Sudden increase in temperature

167.

You are assessing a tornado that has hit landfall for tornadoes. Where on the map would you look for tornadoes relative to its track on land? a. Right frontal b. Right rear c. Left frontal d. Left rear

168.

What least likely contributes to the development of the circulating air mass with low pressure in the middle of a hurricane? a. Adiabatically rising air b. Centrifugal force c. Evaporating water vapor d. Coriolis effect 228

169.

What phenomenon is not a part of the dissipating stage of a hurricane? a. Friction over land b. Warming of the hurricane center c. Cold air over land d. Lack of moisture

170.

What factor is not included in the Milankovitch cycles? a. The distance of the earth from the sun b. How oblique the earth's orbit is around the sun c. The degree of tilt of our axis d. The direction the rotational axis is facing

171.

On what day in our calendar are we most likely to be furthest from the sun? a. January 15 b. July 4 c. September 15 d. April 9

172.

The cycle of our climate that depends on how elliptical our orbit is around the sun is about how long? a. Thirty thousand years b. Seven thousand years c. One hundred thousand years d. 2.5 million years

173.

What would an average tilt be of our earth's axis? a. Five degrees b. Twelve degrees c. Twenty-three degrees d. Thirty-two degrees

229

174.

By definition, how long does a drought last? a. Two weeks b. Three months c. Six months d. It is not defined

175.

What is not considered a type of drought? a. Meteorological drought b. Socioeconomic drought c. Geopolitical drought d. Agricultural drought

176.

What is least likely to be a result of severe drought in the US? a. Wildfires b. Food shortages c. Economic losses d. Increased diseases

177.

What drought phenomenon most likely causes drinking water shortages? a. Lack of wet winters b. Shortened monsoon season c. Infrequent rains d. Agricultural failures

178.

Which type of data collection will not help as much with determining the climate in the early earth years? a. Carbon-14 dating b. Ice core evaluations c. Tree ring evaluations d. Ocean sediments

230

179.

What is not a direct adverse effect of a heatwave? a. Soil erosion b. Loss of marine life c. Crop losses d. Increased risk of infectious diseases

180.

What factor most determines whether or not you are experiencing a cold wave? a. If there is a risk of frostbite b. If there is a rapid rate of temperature falling c. If the temperature is below freezing d. If the temperature is a certain percentage below average for an area

181.

Volcanoes have warming and cooling effects on the earth's climate. What volcanic output is warming rather than cooling? a. Ash b. Sulfur dioxide c. Carbon dioxide d. Lava

182.

What effect does the Arctic oscillation have on the global temperatures of the world. a. It makes the Northern Hemisphere colder than the Southern Hemisphere b. It makes Europe much warmer than North America c. It makes the South Pole colder than the North Pole d. It affects small areas of Europe, North America, and the North Pole

183.

When we talk about reducing the carbon footprint, what type of product or products are we trying not to overuse? a. Metals b. Silicates c. Petroleum d. Water 231

184.

What has been the major cause of the Holocene extinction? a. Climate change b. Human activities c. Global warming d. Competition for resources

185.

What environmental issue is least likely related to the raising of livestock? a. Use of water resources b. Emission of methane gas c. Deforestation d. Pollution of drainage water

186.

What extreme weather situation do you least expect to see as a result of global warming? a. Flooding b. Reduced precipitation overall c. Severe hurricanes d. Heatwaves

187.

Which air pollution substance is most likely to lead to cancer if inhaled? a. Sulfur dioxide b. Particular matter c. Ozone d. Nitrogen dioxide

188.

Which type of air pollution will you likely be able to detect by smelling it? a. Sulfur dioxide b. Particular matter c. Ozone d. Nitrogen dioxide

232

189.

What fuel will burn the cleanest when used for energy? a. Wood b. Coal c. Methane d. Diesel

190.

What kind of air pollution source is much more common in third world countries? a. Vehicle emissions b. Power plant emissions c. Garbage burning d. Wildfires

191.

What is the main effect of ozone in our atmosphere? a. It prevents UV rays from reaching earth b. It prevents infrared rays from reaching earth c. It prevents UV rays from leaving earth d. It prevents infrared rays from leaving earth

192.

We have made steps to reduce the number of CFCs we introduce into the atmosphere. The problem is that CFCs tend to last approximately how long in our atmosphere once released? a. 5 years b. 15 years c. 45 years d. 100 years

193.

Which aspect of the environment or conditions does not support the development of a thermal inversion? a. Windy conditions b. Low-lying areas in the topography c. Evenings or night times d. Snow 233

194.

Most determines the strength of a thermal inversion? a. How much pollution is created b. Temperature differential between the layers of atmosphere c. The length of time of the thermal inversion d. The surface area involved in the thermal inversion

195.

When you are describing thermal inversion, what characteristic is most defined in the inversion layer? a. Cold air b. Smog c. Cooler air trapped beneath warm air surface d. Warm air that is trapping the cooler air

196.

Which element necessary for Los Angeles smog is not a gaseous substance? a. Ozone b. VOCs c. Nitrogen dioxide d. Sunlight

197.

What is the biggest source of Urban air pollution? a. Industrial power plants b. Permanent inversion layers c. Traffic d. Heated homes

198.

If you were a meteorologist in North Africa and will reporting on the levels of PM 10 dust, where would you most expect it to have come from? a. Industrial processes b. The desert c. Home fuel burning d. Vehicles and other transportation sources

234

199.

Which type of acid deposition most contributes to human health issues directly? a. Acid rain b. Acid fog c. Dry acid d. Acid snow

235

ANSWERS TO QUESTIONS CHAPTER ONE 1.

Answer: d. The earth was first formed about 4.6 billion years ago from a ball of gas and dust.

2.

Answer: b. Oxygen was only found later on, after photosynthetic organisms populated the earth and gave off this gas as a waste product.

3.

Answer: b. Nitrogen is the only one of these listed that is not considered a greenhouse gas.

4.

Answer: d. There are great differences in the concentration of water vapor on earth. Its concentration is greatly dependent on the air temperature.

5.

Answer: d. Troposphere. This extends from 0 to 12 kilometers above the earth's surface.

6.

Answer: c. The troposphere is the layer that has all the moisture and winds around the earth. It's because of this that the clouds form, and we have weather.

7.

Answer: a. Each of these features is seen in the thermosphere layer of the atmosphere except for noctilucent clouds, which are seen in the mesosphere.

8.

Answer: c. High temperatures do not define this layer. It is stratified and as little turbulence because the gas density is so low.

9.

Answer: a. The false statement is that the lines begin to intersect; the lines of latitude never intersect.

10.

Answer: d. One atmosphere is the equivalent of 760 torr or 760 millimeters of mercury.

236

CHAPTER TWO 1.

Answer: b. There are many forms of energy to consider. Energy can be transferred from one form to another; in this case, thermal energy or heat is applied to gas molecules, which then have increased kinetic energy or movement.

2.

Answer: d. The temperature gradient between the two objects is what most contributes to the rate of heat transfer in a conduction situation.

3.

Answer: b. About 70 percent of the sun's rays are absorbed by the earth or the atmosphere around it. The rest is immediately reflected back into space.

4.

Answer: d. The greenhouse effect long predated mankind on earth; the concern now is that the greenhouse effect has become accelerated by man rather than caused by our activities.

5.

Answer: a. Dry desert tundra has little moisture it and little vegetation. For this reason, it will lose heat much faster than any wet area or an area with a lot of vegetation.

6.

Answer: c. As you ascend 1000 feet, you can expect a 2 degree Celsius decline in temperature. This means that after 2000 feet, you will experience a decline of 4 degrees Celsius.

7.

Answer: b. The atmospheric gases will trap the heat the earth has absorbed and will most prevent large losses of the heat gotten during the day by the sun.

8.

Answer: c. The rays coming from the sun come in many forms. For the most part, it's the infrared waves that cause the heating of the earth.

9.

Answer: b. Methane is given off by the digestive processes of ruminant animals; it is responsible for a great portion of the greenhouse gas effect.

237

10.

Answer: a. CFCs coming from aerosols and other industrial processes have more than 10,000 times the heat-trapping properties of carbon dioxide, but the concentration is low enough that its overall effect is less than most other greenhouse gases.

CHAPTER THREE 1.

Answer: b. For the most part, you are measuring both the kinetic energy of the molecules of gas in the atmosphere as well as the density of those molecules.

2.

Answer: c. The difference in the width of a degree in Celsius and a degree in Fahrenheit is 1 to 1.8 so every degree Celsius equals 1.8 degrees Fahrenheit.

3.

Answer: b. The best local thermometer is one not near a building or in your car but instead one in the shade about 5 feet from the ground.

4.

Answer: c. Thermometers used to measure the official air temperature in the US are about 5 to 6 feet off the ground in order to avoid any radiating heat from the ground surface.

5.

Answer: c. The bimetallic strip thermometer is made with a strip that has two metals. The metals will expand differently to temperature, which can be calibrated to determine the actual temperature.

6.

Answer: d. These thermometers are expensive and difficult to use but they are not at all sensitive to exposure to the sun's radiation.

7.

Answer: b. Heated probes are used in aircraft in order to prevent buildup of supercooled water vapor on the device. They are slower than other probes, however, because calibrations to account for the heat coming from the device must be made.

8.

Answer: a. Because the sun's rays strike the earth and heat this part only, your highest temperature will be within 1 to 3 centimeters from the earth's surface during the daytime hours.

238

9.

Answer: b. Climate is defined as a stable weather pattern over approximately 30 years in a given region.

10.

Answer: c. The 2 main areas you will see in the United States are dry and temperate. Of these slightly more than half is in the temperate region.

CHAPTER FOUR 1.

Answer: d. Transpiration is the process where plants give off water that goes into the atmosphere as part of the earth's hydrological cycle.

2.

Answer: a. Condensation is what you'll see when you experience dew forming on the grass in the morning as temperatures drop and the air cannot hold as much moisture.

3.

Answer: c. Only about 0.03 percent of existing water on the earth can be found in the atmosphere at any given point in time.

4.

Answer: a. Sublimation results in the highest increase in kinetic energy of water, as it takes water from its frozen state to its gaseous state with no steps in between.

5.

Answer: b. You can do a calculation on any website that has a dewpoint calculator, which would show the point of approximately 54 degrees. The actual dewpoint would be 53.6 degrees. The dewpoint must be less than the temperature of the air as long as the relative humidity is below 100 percent.

6.

Answer: d. At or above the 65 degree mark, you would feel that the air was beyond muggy was oppressively humid.

7.

Answer: b. Upslope fog happens at the base of mountains when winds blow air to higher elevations, where it becomes cooler and cold enough for 100 percent humidity to yield fog.

8.

Answer: a. Advection fog forms often over oceans and rolls inland and back for the ocean every night and every morning for weeks on end.

239

9.

Answer: a. The term nimbus is a root word for rain in Latin; it signifies a cloud that will likely bring rain.

10.

Answer: b. The term "stratus" means spread out so these clouds will often be spread out like a blanket.

CHAPTER FIVE 1.

Answer: b. In any adiabatic process, it is the temperature of the process that remains the same. In the atmosphere, this type of process would involve no exchange of temperature as the molecules move from one place to another.

2.

Answer: d. This air mass would expand and cool. It would expand because it was surrounded by cooler and less dense air and it would cool down as the expansion itself took kinetic energy out of the air parcel.

3.

Answer: c. The wet adiabatic lapse rate is 4.5 degrees Celsius per kilometer change in elevation.

4.

Answer: d. The LCL or lifting condensation level is where the bottom of the cloud layer will be located.

5.

Answer: a. Cumulonimbus clouds also called tower clouds. Because of their height, they have ice crystals near the top and water droplets at the bottom.

These would be called mixed phase clouds.

6.

Answer: b. The average raindrop is 10,000 times greater in the condensation nucleus you see in a cloud. Obviously, these condensation nuclei get much bigger before it falls to the ground.

7.

Answer: c. Deposition freezing involves the process of deposition. If you'll remember, this involves water vapor going to solid without having a liquid phase.

8.

Answer: a. A graupel is another name for a snow pellet. These commonly form inside clouds as different ice crystals collide and make a larger snow pellet.

240

9.

Answer: a. Ice crystals are extremely small and come in several shapes. These are the types of precipitation that cause the phenomenon of ice pillars to be seen.

10.

Answer: b. Freezing rain is essentially supercooled rain that reaches Earth, collects on colder areas such as roadways and results in a sheet of ice. This is quite dangerous to travelers.

CHAPTER SIX 1.

Answer: c. Each of these are conditions you'll see in a high pressure system, except for windy conditions. In a high pressure system, the air is generally calm with clear skies, dry air, and greater variations in diurnal temperatures.

2.

Answer: b. Subpolar low-pressure cells tend to give the cool and rainy weather you often see in the Pacific Northwest. Because this area can extend around the globe, you also see this type of weather in many areas of Europe and near the Antarctic.

3.

Answer: a. The summertime months are the ones most conducive to sea breezes. You need a large body of water, warm land air, and high humidity over the ocean to get these as well.

4.

Answer: a. Winter and nighttime both involve cooler air over land, which promotes land breezes from the land to the sea.

5.

Answer: c. A haboob forms ahead of high winds over a dry and warm desert.

The air in a haboob will be filled with sand and dust particles.

6.

Answer: b. The upper level winds over the US involve the Northeast trade winds that send air from the Northeast to the Southwest.

7.

Answer: b. In the Northern Hemisphere, all low-pressure systems spin counterclockwise and all high-pressure systems spin clockwise.

8.

Answer: c. This line represents a stationary front. It is stalled out to your east so it could mean anything, depending on how this slow-moving front behaves.

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9.

Answer: c. If you can afford one, a Doppler radar system is ideal for telling your constituents when to expect high winds in thunderstorms and other severe weather systems.

10.

Answer: b. According to definition, wind direction at ninety degrees means that it is coming from the east and moving toward the west.

CHAPTER SEVEN 1.

Answer: b. The sun strikes the spherical earth at a greater density of rays than you will see at the poles. This increase in density is what accounts for differential thermal input to our earth over its entire surface.

2.

Answer: a. The net effect across the entire earth is equal input and output; however, there is a net input at the equator and a net output at the poles. That averages out when you include all the data from all parts of the world.

3.

Answer: b. The convergence of two Hadley cells at the equator is where winds are light and there is gently rising air from the ground up to the tropopause.

This is where the doldrums are located.

4.

Answer: d. If you take advantage of the trade winds in the northern hemisphere, you would start out somewhere in Europe and travel them to the Southwest. These are called north easterly winds based on the direction they come from.

5.

Answer: b. Each of these devices will help you detect turbulence in the air, seen in air pockets. The exception is conventional radar, which will not be able to detect this.

6.

Answer: d. Each of these is something that maximizes the chances of air pockets in the atmosphere. Rain clouds do not necessarily trigger these phenomena.

7.

Answer: b. Each of these is a feature you need to have lake effect snows. The exception is balmy temperatures as these types of snow situations often

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happen when the temperatures are quite low. The lower temperatures are necessary for the moist air to begin to precipitate the snow.

8.

Answer: a. For the most part, you will not see lake effect snows later in the wintertime because it has been cold enough to freeze the lake. It is impossible then to steal water from this frozen lake. Therefore, you cannot see lake effect snows.

9.

Answer: d. Because of a rise in the thermocline during El Nino years, there are waters off Peru that are full of nutrients. Fishermen can then catch more fish during those years.

10.

Answer: b. You will see each of these things in an El Niño year; however, you will not see increased rains or monsoon weather in Indonesia because there is less warm air coming there from the equator in the Eastern Pacific.

CHAPTER EIGHT 1.

Answer: c. These letters indicate a maritime or moist air mass that comes from a tropical region. The only choice given that fits for this is the Pacific Ocean.

2.

Answer: a. You need to think about what these letters stand for. The C means that the air mass is coming from a continental region, while P means it is coming from a polar region. This will give you the letters CP.

3.

Answer: c. You will see each of these conditions cold front is passing through; however, you will least likely see layered, stratiform clouds. Instead, you will more likely see thunder clouds.

4.

Answer: a. Each of these features is true of the dryline, except that the moist air will be in the East and the dry air will be in the West.

5.

Answer: b. The main region on earth where you will see a dry and hot source region is the Sahara Desert, which is big enough and stagnant enough to cause this.

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6.

Answer: a. The Arctic Ocean is a major source region for cold and moist air forming an airmass with these characteristics.

7.

Answer: d. In virtually no situation will a cold air front be naturally lifted above a warm one. Remember that it is the warm air that always rises above the cold air.

8.

Answer: b. You will most likely see strong windy thunderstorms with or without tornadoes in the springtime, although it depends on where you live.

9.

Answer: d. You will see mid-latitude cyclones when continental polar air masses form boundary with maritime tropical air masses, giving this designation of CP and MT.

10.

Answer: a. Because of the Coriolis effect, warm moist air will be drawn upward for the right of the cyclone on a weather map with cold dry air extending downward on the left-hand side of the cyclone.

CHAPTER NINE 1.

Answer: c. Where Doppler radar really shines is in its ability study rapidly moving air systems and wind flow patterns such as those you will see your weather systems like tornadoes, hurricanes and thunderstorms.

2.

Answer: d. Deep space satellites exist on earth to monitor incoming solar storms. In order to do this, they must always be facing the sun.

3.

Answer: d. You will see each of these things on a synoptic weather chart or map; however, you will not see a forecast as these charts depict the current conditions only.

4.

Answer: b. You will get each of these values as well as wind speed and direction, dewpoint, and recent barometric pressure changes. The idea is to know if it is okay to fly that day as a pilot.

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5.

Answer: a. Blizzards can involve any amount of snow or temperature; they are mainly defined by the amount of wind generated. A cargo of thirty-five miles an hour usually means a blizzard.

6.

Answer: b. In a snow squall, the amount of time it lasts is relatively short; however it can dump large amount of snow in the region in a very short period of time. This makes them fairly dangerous.

7.

Answer: a. Each of these is a criterion for a red flag warning, although we do not need each of these criteria to have a warning. Ongoing wildfire is not a part of this type of warning.

8.

Answer: b. Any type of weather statement indicates an update of a current situation, including any cancellation of a watch or warning that has been previously issued.

9.

Answer: b. You would issue a hurricane warning if you expected sustained winds in excess of seventy-four miles per hour during a tropical storm, which would indicate a hurricane versus just a tropical storm.

10.

Answer: a. The only place listed where you would not issue a hurricane warning is in Guam. In this case, you would instead issue a typhoon warning.

CHAPTER TEN 1.

Answer: d. Fog is not generally associated with thunderstorms; however, these can be associated with a wide variety of other weather issues, including hail, sleet, strong winds, and tornadic activity.

2.

Answer: a. Ground radiation of heat happens when the sun warms the ground or water surface and air immediately above it. This warm and moist air is then lifted upward, where condensation and cumulus cloud formation occur. Then there are updrafts or convection of this air.

3.

Answer: d. Supercell storms are the most severe thunderstorms and give rise to the greatest number of tornadoes.

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4.

Answer: b. Each of these would declare a thunderstorm a severe thunderstorm except for tornadoes. You wouldn't call it a severe thunderstorm then but would declare a tornado warning instead.

5.

Answer: c. Each of these is an upslope reason to have a flood, except for river debris. This often causes downslope contributions to the development of a flood.

6.

Answer: d. These are all primary adverse effects of flooding except for soil turbulence, which is considered a positive effect of flooding as it can introduce new nutrients into croplands.

7.

Answer: a. A tornado is any funnel cloud that is associated with strong ground winds as well.

8.

Answer: c. You call a system like this a tornado family. Only if there is prolonged activity with supercells or sequences of storms will you use the other terminologies.

9.

Answer: c. If you happen to see a rope tornado, this indicates that the tornado is dissipating and is losing its low pressure system in the center.

10.

Answer: b. The degree of low-pressure you see within a tornado most predicts how long it will last on the ground as it is traveling.

CHAPTER ELEVEN 1.

Answer: d. You could call any storm in the area tropical storm but if it is severe, you would most likely call it a hurricane.

2.

Answer: c. The international dateline is where you would define a tropical storm. West of it, the storm is a typhoon and east of it, the storm is a hurricane.

3.

Answer: b. A tropical disturbance is an area in the tropics where there is a low-pressure system but no rotation or circulation of the winds.

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4.

Answer: c. A tropical storm is defined as an area of winds and circulation in the tropics with sustained winds of at least 39 miles per hour.

5.

Answer: b. Any hurricane of category 3 or more is considered a major hurricane.

6.

Answer: c. The category 5 hurricane must reach winds of at least 157 miles per hour in order to be given this category.

7.

Answer: d. In the Caribbean, storms were originally named according to which Roman Catholic saint was associated with the day the storm first developed.

8.

Answer: c. In terms of dollars lost, the Great Miami Hurricane of 1926 would have cost $178 billion dollars if it happened today.

9.

Answer: b. Hurricanes and other tropical cyclones originate within about five degrees latitude of the equator but then intensify above this level along the ocean surface.

10.

Answer: d. You need to remember that these are non-frontal systems that originate over disturbed warm air that rises and begins to circulate, creating the low-pressure system in the middle.

CHAPTER TWELVE 1.

Answer: c. Each of these will affect the ocean currents, except for precipitation patterns, which will not greatly affect the ocean currents at all.

2.

Answer: d. The salinity of the oceans is higher near the poles. This polar water is cold, drops to the floor and makes its way downward in the deep oceans toward the equator.

3.

Answer: d. When the earth's tilt is less pronounced, our seasons are less extreme and the earth's climate cools, favoring glaciation. We are currently on a pattern toward this phenomenon.

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4.

Answer: a. The earth's wobble is made less predictable by the fact that it is affected gravitationally by the gas giant planets of Jupiter and Saturn. The cycle of this effect is 112,000 years.

5.

Answer: b. Each of these is a positive reason or benefit from having a rainy season. One adverse effect is that the incidence of many tropical diseases that are mosquito-borne is increased during this season.

6.

Answer: c. The definition of a monsoon season is that the winds shift markedly during monsoons, usually seen in Southeast Asia or other parts of Asia.

7.

Answer: a. Each of these drives the density of the water in our oceans. The exception is surface winds, which do not have a direct effect but perhaps a secondary effect on this property of water.

8.

Answer: d. Cold water travels away from the poles in the deeper waters, while warm water comes from the equators to the poles in the surface water.

9.

Answer: d. Carbon dioxide is the major contributor to the global warming we are seeing as it is the most damaging greenhouse gas.

10.

Answer: a. The temperatures and sea levels on earth will continue to rise by 2100, even if we curb our fossil fuel use immediately.

CHAPTER THIRTEEN 1.

Answer: d. Almost all air pollution diseases due to particulate matter are lungrelated, causing these diseases. Eczema of the skin would be less likely from particulate matter.

2.

Answer: a. Diesel trucks and other engines on the roadways are major sources of nitrogen dioxide in the atmosphere so you will see higher levels where these are present.

3.

Answer: d. Volatile organic compounds from aerosols and indoor products most contribute to indoor air pollution when the ventilation is poor.

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4.

Answer: b. This methane gas is given off by the animals' GI tracts but is not a part of the animals' metabolism. It is given off by the bacteria in the GI tracts of these animals.

5.

Answer: b. The three things you need to make ozone on the ground are sunlight, VOCs, and nitrogen oxides. These things need to chemically interact in order to make ozone.

6.

Answer: c. Each of these risked having too much ground-level ozone near the earth's surface. There is no increased risk of sunburn unless you are talking about a reduction in ozone in the upper atmosphere as part of CFC activity interacting with our existing ozone layer.

7.

Answer: c. Both sulfur dioxide carbonaceous particulate matter are seen in London fog but not in Los Angeles smog, due to the ways it is made.

8.

Answer: a. Each of these is a major component of Los Angeles smog, except for carbon dioxide which is not a component of any type of smog.

9.

Answer: a. Each of these can contribute to acid deposition to the earth's surface. While wind can allow these other things to travel distances, it does not contain these substances by itself.

10.

Answer: d. While all of these can contribute to acid rain, it is actually the power plants and factories that burn fossil fuels in order to make electricity for us that contribute most to the acid rain in our environment.

CHAPTER FOURTEEN 1.

Answer: d. White light coming from the sun does not have a specific wavelength. Instead, it is a range of wavelengths from 750 to 400 nanometers, which is the visible wavelength range.

2.

Answer: b. Violet is light with the shortest wavelength, but we do not see this as the color of the sky because our eyes are not particularly sensitive to the violet color.

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3.

Answer: c. A red object will absorb many colors but will absorb the green color the most.

4.

Answer: a. Infrared rays are heat waves emitted by the sun; these provide us with the heat energy we use to keep the entire planet warm.

5.

Answer: d. Without any atmosphere to scatter any of the sun's rays, sunset and all other times on the moon would show a white coloration. This is the summation of all light energy waves emitted from the sun.

6.

Answer: b. A waning gibbous moon is one where the moon is disappearing but has not yet reached its third phase.

7.

Answer: c. A blood moon is a reddish coloration to the moon but you might see a full lunar eclipse, in which the light reflected off of the moon comes from around the periphery of the earth.

8.

Answer: b. A blue moon happens when you see to full moons in the same calendar month. This occurrence happens approximately every 2 ½ years.

9.

Answer: a. You need an unobstructed view of the horizon they very clear day to see a green flash at the time of sunset. You can also see it from a tall building or airplane or mountaintop. A rainy day or rainstorm might obstruct your view.

10.

Answer: d. If you remember the phrase Roy G. Biv, you will know that after the yellow and heading toward the violet end of the spectrum, you will see the color green.

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COURSE ANSWERS 1.

Answer: d. Both methane and carbon dioxide helped keep the earth warm in its early days, even as the sun was not as bright.

2.

Answer: a. Plants were responsible for the large deposition of waste carbon onto the earth. This carbon later became things like petroleum and other carbon products used today.

3.

Answer: c. The Eocene epoch was a time of increased global temperatures in recent millennia so that trees and animals inconsistent with the northern latitudes today thrived in that environment.

4.

Answer: b. The percent volume of nitrogen in the air is nearly 78 percent.

5.

Answer: a. The percent volume of oxygen in dry air is relatively stable throughout the earth at around 21 percent.

6.

Answer: b. The exosphere is by far the widest layer of our atmosphere, extending from 700 to 10,000 kilometers.

7.

Answer: b. Stratosphere. This is where you will exclusively see the ozone layer.

8.

Answer: d. The stratosphere has polar nacreous clouds in it; these are essentially the only clouds you'll see routinely in this layer.

9.

Answer: b. The heat in the thermosphere is barely felt because the hot gas molecules are so far apart; the air is not very dense at all in this layer.

10.

Answer: b. The ionosphere is made by the ionization of particles from solar radiation. This phenomenon creates the aurorae.

11.

Answer: d. 1° longitude or latitude is about 69 miles anywhere on the earth.

12.

Answer: c. The prime Meridian was arbitrarily selected to be in Greenwich England.

13.

Answer: b. Of these choices, latitude by itself has no impact on the air pressure, while the others do affect it.

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14.

Answer: a. Each of these is a factor in measuring air density except for volume, which is used to calculate density but does not affect it.

15.

Answer: c. Plant grow lights will emit heat that is radiating from the lights to heat the plants. This is the only example of radiation among these choices.

16.

Answer: a. Thermal energy transfer with convection means that heated liquid or gaseous media expand, become less dense, and rising from the bottom the top of the system.

17.

Answer: c. A higher albedo means more light is reflected as it arrives from the sun. The poles are known to have the highest albedo on earth.

18.

Answer: b. There is a balance of heat on earth because the heat taken in by the equator moves to balance the deficits in the poles. About 20 percent of the equatorial heat gets transferred to the poles.

19.

Answer: d. September 20th is the day of the autumnal Equinox; the rate of day change is the fastest with the days getting shorter. This is because the sunrise and sunset are on a sine curve.

20.

Answer: a. December 20th is marked by the sun crossing high above the Tropic of Capricorn; this represents the shortest day of the year in the Northern Hemisphere.

21.

Answer: a. UVA and UVB rays are both responsible for the development of sunburn by damaging the skin surface. The rays are long enough, however, that they do not get far into the body to do any internal damage.

22.

Answer: d. Water vapor contribute to more than half of the greenhouse effect.

This has been true since the earth had gaseous water around it as part of the atmosphere.

23.

Answer: d. Carbon dioxide comes from these two major sources. Combustion of plants as is seen in deforestation also affects the CO2 levels on earth.

24.

Answer: b. Carbon dioxide levels have increased greatly from industrialization that has led to burning of fossil fuels and deforestation practices.

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25.

Answer: d. The standard international unit for temperature. It is used in many scientific circles but not used much in meteorology because it is wieldy and the common person does not know this scale.

26.

Answer: c. The Stevenson screen will protect the thermometer inside from the effects of each of these things, except for humidity, which does not actually affect thermometers at all.

27.

Answer: d. The temperature is always rising in the thermosphere but just above the mesopause, the rate of temperature change is the greatest.

28.

Answer: b. The highest recorded temperature on earth to date is 54 degrees. If you reached a temperature of 55 degrees, this would just exceed the world record.

29.

Answer: a. Each of these is a downside to using liquid in glass thermometers in large-scale meteorology except for inaccuracy. These are very accurate and stable instruments for recording temperature.

30.

Answer: b. The radiometric thermometer is a lot like an infrared heat sensor that can say gradations and can be calibrated to some accuracy but will not be completely accurate in giving local air temperatures.

31.

Answer: a. Only the radiometric temperature sensor could efficiently be used with satellites to get a water surface temperature reading.

32.

Answer: c. The radiosonde has sensors that measure air pressure, air temperature, and humidity but not wind speed.

33.

Answer: d. You would expect a maximum temperature at about three to five PM, because the earth stores heat before radiating it back to the atmosphere.

This accounts for the lag time between high noon and the maximum temperature you experience in the neighborhood.

34.

Answer: c. In reality, higher elevations mean that the earth cools more rapidly and that there will be a higher diurnal variation in temperature in those locations.

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35.

Answer: b. The major factors determining climate are temperature, amount of precipitation, and timing of precipitation.

36.

Answer: d. In reality, Russia is in a relatively high latitude situation and is away from large bodies of water, so it is mostly in the continental climate region.

37.

Answer: a. While coconut trees will grow in some other areas, they certainly grow best in tropical regions where there is year-round moisture and heat

38.

Answer: c. The precipitation in the region will cause a 6 degree decline in the temperature after 1000 meters.

39.

Answer: b. Each of these involves a direct phase change in water, except for percolation, in which water flows from one area underground to another in the same phase as a liquid.

40.

Answer: c. The 2 major processes that transfer water between the air and the ground are evaporation and precipitation. Other factors play a minor role.

41.

Answer: d. The vast majority of water on earth exists in our many oceans.

42.

Answer: d. The phase change of condensation results in a decrease in kinetic energy of the water molecule of 600 calories per gram. The only phase change decrease greater than this would be deposition.

43.

Answer: b. Evaporation is the entire basis of sweating. When you sweat, energy is taken from your body to help the evaporation take place on your skin. This heat is lost from your body, so you are cooler.

44.

Answer: c. Only in windy conditions will you have evaporation favored but condensation somewhat more inhibited. The other factors will either favor condensation or will favor both phase changes.

45.

Answer: a. Had there been a dry day the previous day, there would be little water vapor in the air and the chances of dew would be reduced.

46.

Answer: c. Hoarfrost conditions are seen in all of these situations except for sunny days, which will not promote this type of sublimation.

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47.

Answer: d. You need each of these conditions have proper fog formation. In general, fog occurs on cooler days where the temperature is close to the dewpoint.

48.

Answer: c. Condensation nuclei can be made of many different things; however, they are not generally made out of pre-existing water droplets. It is hard for water droplets stick to themselves and condense without some other aerosol contributing to the nucleus.

49.

Answer: d. Cirrus clouds are considered high-level clouds. The rest of these are all low-level clouds.

50.

Answer: b. These clouds are often early harbingers of an incoming warm front.

51.

Answer: c. Cumulonimbus clouds are also called tower clouds; they extend many kilometers into the air and lead to short deluges of rain.

52.

Answer: d. Cumulus clouds are small puffy clouds that come in unique shapes and signal good or fair weather.

53.

Answer: c. In an air parcel the temperature and pressure are always the same throughout the air parcel. It can be any size or volume.

54.

Answer: b. The actual dry adiabatic lapse rate of air mass is 9.8 degrees Celsius per kilometer. This is approximately 10 degrees Celsius per kilometer.

55.

Answer: a. Temperature of an air parcel is the factor that most determines where it sits in relation to other air masses in any given environment and at any altitude.

56.

Answer: c. Sounding involves a weather balloon with a radiosonde that will measure temperature, pressure, and other parameters as the weather balloon ascends in order to get a complete picture of the temperature differential at a specific location.

57.

Answer: a. The diagram is able to plot the line between saturated and unsaturated air using temperature as the x axis and % saturation as the y axis.

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58.

Answer: b. Contrails are also called condensation trails. They are caused by vapor being released by aircraft as they are flying through the sky. Many of these in one spot often look like clouds.

59.

Answer: c. You exhale moisture laden warm air from your body, which sends moisture to air that cannot tolerate so much of it at that temperature. The end result is cloud formation.

60.

Answer: d. Each of these would contribute to aerosols in the atmosphere; these would cause cloud condensation nuclei, which would contribute to rain.

Recent rain would wash these aerosols out of the atmosphere so it would not contribute aerosols to the atmosphere.

61.

Answer: c. Sodium chloride is salt, which is very hygroscopic and attracts water vapor at relatively low levels of humidity.

62.

Answer: b. Any type of deep cumulus cloud as the cumulonimbus cloud will have updrafts, which allow raindrop to spend a longer time within the cloud.

This leads to larger raindrops.

63.

Answer: a. Water can be supercooled to as low as -40 degrees Celsius before it must be solid, regardless of the conditions.

64.

Answer: d. Homogeneous freezing involves supercooled liquid droplets that become solid in absence of any nucleus. The temperature needs to be below 40 degrees Celsius in order to have this.

65.

Answer: b. If a raindrop is less than 0.02 inches in diameter, you would call it drizzle unless the raindrops themselves were scattered far apart as they fell.

66.

Answer: c. Any clump of ice greater than one fourth inch diameter is referred to as hail, although hail can be much larger than this.

67.

Answer: d. Snowflakes are the only type of frozen precipitation that is actually in the shape of a real ice crystal would see microscopically. You know this as the 6 pointed star shape.

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68.

Answer: d. The tipping bucket rain gauge tips whenever it is full. This means you will get data anytime the bucket is tipping, which is when you get a recording. In harder rain, the bucket will tip faster.

69.

Answer: a. A tipping bucket rain gauge is the only rain gauge that actually measures the depth of the rainfall. The others measure other aspects of rain besides the depth.

70.

Answer: c. A Doppler rain sensor specifically detects the rate or speed of rainfall, but does not detect the actual depth of rain or size of raindrops.

71.

Answer: c. Subtropical high-pressure air passes are seen above or below the equatorial regions. The air is very warm and dry, with much of the water vapor being sucked into the equatorial regions.

72.

Answer: a. One of the main reasons why air pressure is higher at the poles and lower at the equator is because the earth is not completely spherical and effects of gravity or greater at the poles as result.

73.

Answer: d. Each of these will affect the air pressure with the exception of air composition, which plays no role in actual air pressure changes on earth.

74.

Answer: b. The phenomenon of advection means there is horizontal flow of air on the ground from high-pressure to low-pressure. You experienced this as wind.

75.

Answer: b. You need high plateaus to have a high enough land mass to cool down in winter; this allows air to flow at high velocities down to the lower elevations.

76.

Answer: c. You need each of these things to cause a Chinook winds, except for a desert, which is not necessary for these winds but is created by them instead.

77.

Answer: d. Santa Ana winds cause dry and hot air to blow westward over areas that are already dry. This can precipitate the rapid spread of forest fires, leading to devastation of homes and communities nearby.

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78.

Answer: a. The terms haboob, dust devil, and whirlwinds are related to hot and dry winds kicking up desert dusts. You will get monsoon rains but not blizzards.

79.

Answer: d. There are three major convection cells per hemisphere, which leads to a total of 6 cells around the earth.

80.

Answer: a. The boundary between the polar and Ferrell cells is what creates the polar jet stream. It is fast moving air because of the temperature difference between these cells.

81.

Answer: c. Earth's rotation causes air flow to be shifted to the right or eastward in the Northern Hemisphere and to the left or westward in the southern hemisphere.

82.

Answer: a. A trough is a section of low-pressure on a weather map, while a ridge is similar but represents an elongated section of high-pressure.

83.

Answer: a. The line shows a coming cold front and indicates that rain or snow would be likely in your area soon.

84.

Answer: b. Anemometers can be purchased for individual use. These can predict the wind speed and direction in your area.

85.

Answer: c. At 60 degrees north or south latitude, you will see the greatest deficit of heat on the earth's surface. This is explained by the incoming angle of the sun's rays and the amount of heat loss exhibited at this latitude.

86.

Answer: b. If there were just one cell between the equator and the poles, it would be called the Hadley cell. On the surface, there would move from North to South.

87.

Answer: a. In the doldrums, which is near the equator, you will see each of these things except for clear and sunny skies. There is too much humidity in the air and too much cloud formation to have sunny skies.

88.

Answer: a. The area over Hawaii is called the Pacific high or the Hawaiian high. This is a semipermanent area of high pressure.

258

89.

Answer: c. Remember that a trough is a long line where a low-pressure system would be. Along the equator is the equatorial trough.

90.

Answer: a. Both land breezes and katabatic breezes tend to occur during the nighttime hours.

91.

Answer: a. Each of these is a major factor in the development of turbulence and wind shear. This is not seen if there is just one mountain. It takes a mountain range to do this.

92.

Answer: c. Flying at constant altitude will not generally cause clear air turbulence, but the others can do this. Need to understand, however, that nothing will totally prevent this phenomenon.

93.

Answer: d. Eddies are formed when strong winds approach rough terrain.

After going through the terrain on the leeward side, swirling eddies can be seen.

94.

Answer: c. Hurricanes always develop near the equator at the equatorial lowpressure regions. As you know is a low-pressure belt around the earth at the equator. It is from this belt that hurricanes begin.

95.

Answer: b. Each of these contributes to the cooling of the Eastern Pacific compared to the Western Pacific Ocean. The natural tilt of the earth wouldn't contribute to this cooling.

96.

Answer: c. Under normal conditions, the Walker circulation allows cooler and drier air to flow along the surface above the ocean area where it warms and becomes more moist. This leads to more precipitation in the area.

97.

Answer: a. As a result of global warming, the frequency of El Niño years has increased and has been an increase in the intensities of both extremes in the southern oscillation.

98.

Answer: c. A La Niña year will be a time when you see each of these features except that there will be 4 fishing along the coastline of Peru and Ecuador due to lack of nutrients in the water and a lowering of the thermocline.

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99.

Answer: b. You would choose the letters CA because the air mass would come from a continental area and it would come from the Arctic. This leads to the specific designation of CA.

100.

Answer: d. You would not describe an air mass as being windy or calm.

Instead, you would use terms to suggest its warmth or humidity. By definition, an air mass itself will not be windy.

101.

Answer: d. The warm and moist air on the east side of the dryline in the US comes from the moister air in the Gulf of Mexico.

102.

Answer: c. The source region must hang onto its airmass for about a week before the air can attain the characteristics from the source region.

103.

Answer: c. In areas of Canada to the North you will get air masses with stable and uniform characteristics that are both dry and cold.

104.

Answer: d. This would be a maritime equatorial air mass so you would label it with the mE designation.

105.

Answer: a. An occluded front is one that is in front of a low pressure system.

The weather is extremely severe behind these systems. They represent areas where a cold front overtakes a warm front.

106.

Answer: c. The latitude cyclones can be far larger than hurricanes. They are also located much more to the North and do not originate in the tropical areas as is true of hurricanes.

107.

Answer: d. The mid-latitude cyclones will always rotate counterclockwise and in all cases they will have a low-pressure system in the center.

108.

Answer: b. Nor'easters are very intense low pressure cyclones that will carry strong winds and heavy storms along the eastern seaboard.

109.

Answer: c. Alberta clippers you not carry much precipitation but are very fastmoving storms. They tend to be dry because there is no moisture in the areas they develop.

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110.

Answer: a. Geostationary satellites take pictures of the same part of the earth every thirty seconds or so.

111.

Answer: b. Polar satellites travel in a north south direction from pole to pole so that they are able to capture an entire image of the rotating earth twice per day.

112.

Answer: c. Each of these represents a phenomenon on earth that is easily caught using a polar satellite. They are much harder to capture on a geostationary satellite, except for hurricanes which are easily shown in their entirety on this type of satellite.

113.

Answer: a. Each of these is something that is gathered through these automated weather systems. The exception is the sunrise and sunset time, which is predicted through other means.

114.

Answer: c. The global data assimilation system can take information from different forecasts and different systems around the world to get a current forecast that is as accurate as it can be, with sixteen days advance warning as to the weather.

115.

Answer: c. The climate forecast system can predict the seasons in a reasonable period of time up to about nine months in advance.

116.

Answer: a. Each of these is part of how we forecast the weather in some way.

The rapid refresh system gives us an hour by hour forecast of the weather eighteen hours in advance.

117.

Answer: c. The weather depiction chart is a map of an area for meteorologists and aviators. It shows weather conditions but does not show temperature.

118.

Answer: c. The weather prognostic chart will help you get the weather for flying up to 48 hours in advance of a trip. These charts only go up to this point in predicting the weather.

119.

Answer: d. Downbursts involve heavy, strong downward winds that strike the ground at the leading edge of a storm. These can be very damaging even though they are not tornadic.

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120.

Answer: a. Hook echoes on radar will show the presence of a probable tornado in the area of large thunderstorms.

121.

Answer: b. Each of these is a visible feature of a thunderstorm. You will not be able to see hook echoes with the naked eye unless you have a Doppler radar.

122.

Answer: c. Scud clouds are clouds with ragged edges that hang low enough to sometimes touch the ground on the backside of a thunderstorm. While confused often with tornadoes, these are not dangerous.

123.

Answer: d. Each of these can cause coastal flooding; however, you will not see this with sea breezes that tend to be fairly innocuous.

124.

Answer: d. While the common definition of heavy snow is six inches in twelve hours, this is somewhat inaccurate as snows in the southern part of the United States can be called heavy snow with half that much snowfall rate.

125.

Answer: c. The designation heavy snow warning is no longer in use. The term Winter storm warning applies to all sorts of inclement winter weather.

126.

Answer: b. The criteria for a Winter weather warning is broad and includes weather that is either imminent, ongoing, or expected within forty-eight hours.

127.

Answer: a. The tornado emergency is most severe and indicates the greatest potential for loss of life because it indicates the tornado is large and is approaching a major metropolitan area.

128.

Answer: b. While severe thunderstorm watches can last up to eight hours, warnings last only up to one hour in total duration.

129.

Answer: c. The cutoff for a severe thunderstorm warning is fifty-eight miles per hour. Above this, you would indicate this type of warning. Below this, you would indicate a severe weather advisory.

130.

Answer: d. A flash flood warning generally means is been a sudden event leading to actual flooding or imminent flooding. It would least likely be issued in the case of gradual snowmelt.

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131.

Answer: c. When you issue an areal warning, you mean to indicate a small area, such as a river, stream, storm drain area, or street. There are separate flood warnings for coastlines.

132.

Answer: d. While most of these can indicate flooding near the coastlines for any reason, a storm surge warning is issued almost exclusively for hurricanes or tropical cyclones.

133.

Answer: b. You would release a beach hazard statement if there was some kind of biological hazard along the shoreline to include red algae growing nearby.

134.

Answer: a. So far, extreme cold mornings only issued in Alaska and are only issued when the air temperature is less than forty degrees Fahrenheit.

135.

Answer: c. If you expect the temperatures to fall to twenty-eight degrees Fahrenheit or lower, you would likely issue a hard freeze warning to the area if crops were involved.

136.

Answer: d. You need to issue each of these warnings and watches during the growing season in a given area where crops are being grown. The exception is the wind chill advisory, which is not associated with crops or crop losses.

137.

Answer: b. The thunderstorm dissipates when the downdrafts exceed the updrafts.

138.

Answer: d. Downdrafts are caused by colder air in the tall thunderclouds. This air is laden with heavy rain so the combination of factors causes air to drop downward.

139.

Answer: c. A cell is defined according to the number of updrafts associated with the thunderstorm. A single-cell storm has just one updraft in it.

140.

Answer: a. The bow echoes inside a thunderstorm will be most associated with straight line winds but will have a variety of storm-related phenomena as well.

141.

Answer: c. Each of these is a weather system seen with mesoscale convective systems. The exception is blizzards, which are not seen with these systems.

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142.

Answer: a. These are all reasons that contribute to having a flash flood. The exception is snowmelt, which tends to be gradual and much more predictable.

143.

Answer: d. Each of these is a reason you might see coastal flooding. The exception is snowmelt, which is not a common reason for coastal flood.

144.

Answer: b. Each of these can cause flooding but tsunamis can definitely contribute to a catastrophic flood.

145.

Answer: a. Perhaps the most important thing you need in order to have the ability to predict floods in a given area is historical records showing past flooding. These are combined with present-day information in order to predict whether or not a flood will occur.

146.

Answer: c. The most severe rating on the enhanced Fujita scale is an EF5 tornado. The EF scale goes from zero to five.

147.

Answer: b. Each of these is a factor used to describe a tornado that is also used to rate a tornado on a common rating scale. The exception is eyewitness accounts, which are not needed to create these ratings.

148.

Answer: d. A tornado is defined as a wind vortex extending from cloud to ground. It can have varying intensities and differing levels of damage to ground structures.

149.

Answer: b. You need surface winds of at least 40 miles per hour in order to call something a tornado. If you do not see this, you will call it a funnel cloud.

150.

Answer: d. You would designate a waterspout as a tornado only if land was somehow affected because of the waterspout's activity.

151.

Answer: a. Tornadoes begin their life cycle as mesocyclones. They then pull down from the clouds and draw in moist downdraft air as they continue to develop.

152.

Answer: b. The definition of hurricane is made by having sustained winds of greater than 74 miles per hour.

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153.

Answer: a. Hurricane season in the Northern Hemisphere ends on November 30th.

154.

Answer: c. In this part of the world, hurricane season begins on June first.

155.

Answer: d. The maximum known lifespan of a hurricane is 31 days in which the hurricane met the criteria for being one. This was Hurricane John in 1994.

156.

Answer: a. These early hurricanes or tropical depressions begin as disorganized and stormy areas along the west coast of Africa, traveling in our direction along with the trade winds.

157.

Answer: d. You will define a storm as being tropical depending on where it gains its energy. It will get its energy from the ocean if it is tropical but will get its energy from the atmosphere if it is not tropical.

158.

Answer: c. Of the 100 tropical cyclones we get each year, only about half or 50 of these become mature hurricanes or typhoons.

159.

Answer: d. When a tropical storm reaches its 39 mile per hour mark or more, it is named and keeps its name as it progresses to become a hurricane, if it will do this at all.

160.

Answer: d. All categories of hurricanes will be dangerous, even category 1 storms.

161.

Answer: d. Each level is four times as great as the next. If you go up two levels, you would increase the damage by a factor of 16.

162.

Answer: a. The eyewall or wall cloud is the ring of cumulonimbus clouds surrounding the eye of the hurricane.

163.

Answer: b. The intensity is determined by measuring the winds at 10 meters above the ground.

164.

Answer: a. The 1900 Galveston Hurricane cost the area as many as 12,000 lives. This was followed fifteen years later in the same area by another than killed 8000 more people. They built a seawall after this.

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165.

Answer: b. Lightning is not particularly common or dangerous in hurricanes or other tropical cyclones. The other phenomena, however, are very dangerous.

166.

Answer: c. Squall lines in a hurricane represent a sudden increase in wind speeds, which can be extremely damaging to lives and property.

167.

Answer: a. Most tornadoes are concentrated in the right frontal area of the hurricane or other tropical cyclone.

168.

Answer: c. Each of these is an aspect of hurricane rotation and the development of the low pressure in a hurricane except for evaporation, which does not play a role in this process.

169.

Answer: b. The main issues that dissipate the storm include increased friction over land, passage of the storm over cooler air, and lack of moisture to feed the hurricane. They cool down rather than warm up as they dissipate.

170.

Answer: a. Each of these is a major factor that plays into the Milankovitch cycles; however, the distance of the earth from the sun is not necessarily part of this directly.

171.

Answer: b. On or about July 4, the earth is furthest from the sun so we get fewer of the sun's rays during that time. We are closest to the sun in early January.

172.

Answer: c. The cycle that depends on how elliptical the Earth's orbit is around the sun spans approximately one hundred thousand years. It affects the difference between the amount of the sun's rays we get in the summertime versus the wintertime.

173.

Answer: c. The earth is tilted on its axis in a range of between 22.1 to 24.5 degrees. It varies on a forty-one thousand year cycle.

174.

Answer: d. Droughts are defined not by length of time but by their severity so they need to be severe enough to affect water supply and crops only. There is no minimum time frame.

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175.

Answer: c. Each of these is a type of drought, except for geopolitical drought.

Added to this list is hydrological drought to round out the four types of drought.

176.

Answer: d. Each of these is an issue you can get from drought in the US, except that it doesn't necessarily increase the risk of diseases.

177.

Answer: a. Lack of wet winters reduces the snowmelt in spring. This has the greatest effect on the amount of drinking water to many different areas of the world.

178.

Answer: a. Each of these is a situation where there is information gotten about the early climate. Carbon-14 dating is not particularly helpful in this process.

179.

Answer: d. While you will see each of these factors as a direct adverse effect of a heatwave, you will not see an increased risk of infectious diseases. Instead, you will see a risk of hyperthermia in humans.

180.

Answer: b. A cold wave is mostly determined by the rate at which the temperature falls, usually defined as a rapid temperature reduction within twenty-four hours.

181.

Answer: c. Each of these will cool the earth and has a disruptive effect on our climate. The exception is carbon dioxide, which is a warming greenhouse gas.

182.

Answer: d. The Arctic oscillation is minor and doesn't affect the globe as a whole. It will alter the North Pole temperatures and those of parts of Europe and North America in minor ways.

183.

Answer: c. The carbon footprint relates to the overuse of petroleum products, which are basically made of carbon and hydrogen. This is why we talk about the carbon footprint.

184.

Answer: b. The description of the Holocene extinction involves all human activities that have led to the decline and extinction of resources.

267

185.

Answer: a. Each of these is related to raising livestock and is causing an environmental hazard. The exception is use of water resources, which is not really as big a problem as the rest of those listed.

186.

Answer: b. You will see each of these events, but the exception is reduced precipitation overall. Some areas will be wetter, while others may be drier instead.

187.

Answer: b. Particulate matter is most likely to stick in the lungs or leach toxins into the bloodstream, leading to a higher risk of cancer not seen when you inhale other types of air pollution.

188.

Answer: a. Sulfur dioxide is noticeable by its smell. It smells like rotten eggs at very low concentrations in the air.

189.

Answer: c. Methane is part of natural gas, which is a fossil fuel found deeper in the earth. It has the ability to burn more cleanly than other petroleum products, wood, and coal.

190.

Answer: c. Garbage burning is a major problem in places like India, where they tend to burn garbage as a way to get rid of it rather than putting it in landfills, etcetera.

191.

Answer: a. Ozone exists as a layer around the earth's atmosphere. It absorbs UV rays entering the atmosphere from the sun.

192.

Answer: d. CFCs stay in the atmosphere from between 55 to 140 years, with an average of approximately one hundred years. This means that our reduction in CFC production will not eliminate the problem for quite some time.

193.

Answer: a. Each of these has the potential to worsen a thermal inversion, except for wind. Windy conditions will mix the atmosphere and actually lessen an inversion.

194.

Answer: b. The strength of a thermal inversion is largely determined by the temperature differential between the different layers of the atmosphere involved in the inversion.

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195.

Answer: d. When you talk about thermal inversions, you are talking about the warm air that is trapping the cooler air beneath it as being the inversion layer itself.

196.

Answer: d. You cannot get Los Angeles smog without sunlight, which is not a gaseous substance. Nevertheless, sunlight facilitates the process of developing smog from ground emissions.

197.

Answer: c. The high density of traffic seen in urban areas is the most common cause and the largest contributor to Urban air pollution.

198.

Answer: b. In areas of the Middle East and northern Africa, particulate matter mostly comes from the desert in the form of dust as well as from Dusty roadways.

199.

Answer: c. Dry acid is more dangerous to humans than any other type of acid deposition, because these particles can enter human lungs and endanger our health directly.

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