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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere

The Atmosphere

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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere

• How big is the atmosphere? • Why is it cold in Geneva? • Why do mountaineers need oxygen on Everest?

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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere

• A relatively thin layer of gas over the Earths surface

• Earth’s radius ~ 6400km • Atmospheric thickness ~ 100km http://www.alpix.com/3d/worldwin/ WW_Atmosphere_1_m.jpg

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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere 36

Air Pressure and Altitude

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• Pressure decreases as you • The change in is pressure is not linear. Pressure decreases exponentially with altitude.

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Altitude (km)

go up in height.

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20 16 12 8

Height of Mt Everest

50% of air below this altitude

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0

200

400

600

Pressure (mb)

800

1000

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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Air Density and Altitude

• Gravity pulls all particles down

• More particles at the

bottom of the air column

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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere 500

400

Altitude (km)

Air Molecules

As gravity pulls gas molecules to the Earths surface an pressure of 100Kpa is exerted at sea level

1013.25mb

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Air Density 200

100

Air Pressure

0 Low

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High Increasing

Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Layers and Temperature

• The atmosphere can be divided into layers based on temperature characteristics

• The layering creates real physical barriers. • Mixing occurs within layers but not between layers 7

Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere 120

Layers of the atmosphere

• • Stratosphere • Mesosphere • Thermosphere

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Troposphere

Thermosphere Mesopause

Altitude (km)

80 Mesophere 60 Stratopause 40 Stratosphere 20 Tropopause Troposphere 0

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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere 120

Layers of the atmosphere

100

Thermosphere 0.001mb Mesopause

Altitude (km)

80

Four layers are defined by trends in average air temperature

0.01mb Mesophere 0.1mb

60 Stratopause

1mb

40 Stratosphere 20 Tropopause Troposphere

10mb

100mb 1000mb

0 -100 -80 -60 -40 -20

0

20

40

60

Temperature oC

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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Troposphere The habitable layer of the atmosphere

• • • • •

Contains 80% of the atmospheres mass Between 8-16 km deep Deeper at equator than at the poles The part of the atmosphere that contains weather

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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Stratosphere

• • •

Contains the ozone layer

The stratosphere is warmer than the top of the troposphere because of the energy absorbed

Where ultra-violet radiation is absorbed Protects us from harmful high-energy radiation from the sun

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120

Topic 3: Global Cycles and Physical Systems 100

Thermosphere 0.001mb

Mesopause

Altitude (km)

3.1: 80The Atmosphere

0.01mb

Mesophere

Stratosphere 60

0.1mb

Stratopause

1mb

40 Stratosphere 20 Tropopause Troposphere

10mb

Warming in the Stratosphere

100mb 1000mb

0 -100 -80 -60 -40 -20

0

20

Temperature oC

40

60

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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Ozone

• •

Highly reactive molecule oxygen O3 Two types - Stratospheric and Surface ozone O

O

O

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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Surface Ozone

Result of chemical reactions between a variety of polluting gases

• •

Mainly from vehicle emissions An irritant

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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Stratospheric Ozone

• • •

Beneficial - absorbs ultra-violet radiation Protects us from this harmful radiation Gets down by chemical reactions with chlorine containing gases (chlorofluorocarbons – CFCs): Manmade compounds used in aerosol sprays, refrigerators and air-conditioners

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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Mesosphere

• • •

Between an altitude of 50 - 85 km

This results in no heating taking place

Temperature drops with altitude to about -90oC Little or no gases, particles or water vapour to absorb UV

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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Thermosphere

• •

Extends to the exosphere at about 110km

• •

Thin layer that contains many ions (charged)

The upper layer of the mesosphere and the thermosphere are called the ionosphere

Responsible for the Northern and Southern Lights and the reflection of radio waves

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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere

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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Lapse Rate

• • •

In the troposphere temperature decreases with altitude

Averaged as the Environmental Lapse Rate (ELR)

This varies from place to place and season to season The amount of moisture in the air has a large effect on the lapse rate

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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Lapse Rate

• • •

ELR is around 6.5oC / 1000m This works for about the first 11 km of atmosphere But the idea that temperature falls in the troposphere is important

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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Atmospheric Energy Budget

Sunlight (short wave radiation)

• •

Controls weather and climate Drives photosynthesis

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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere

ENERGY IN THE ATMOSPHERE Incoming solar Radiation Reflected Solar Radiation

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Outgoing Longwave Radiation

342 Reflected by Clouds and Atmosphere

Emitted by Atmosphere

77

165

Atmospheric window

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Absorbed by

67 Atmosphere 78

Greenhouse Gases

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Latent Heat

350

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Back Radiation

Reflected by Surfaces

30 168

390

Thermals

Surface Radiation

Absorbed by surfaces

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Evapotranspiration

324

Absorbed back Radiation

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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Energy in the Atmosphere

Solar radiation can take several paths within the atmosphere

• • •

30% reflected by the atmosphere 19% absorbed by the atmosphere 51% absorbed by Earth’s surfaces

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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere 100% Solar Radiation 6% Reflected by atmosphere 20% reflected by clouds

19% absorbed by the atmosphere and clouds

4% reflected from surfaces

51% absorbed at the surface

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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Energy in the Atmosphere

UV absorption by ozone, water vapour carbon dioxide and dust and ice particles

• •

Reflection by clouds and surfaces The remainder heats up the Earth in the natural greenhouse effect

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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Differences in Solar energy across the Earths surface

Because of the curve of the Earth different values of solar energy/unit area occur

Least solar energy / unit area is at the poles

Most solar energy / unit area is at the equator

Solar Radiation

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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Differences in Solar energy across the Earths surface

Albedo effect is the balance between a surfaces ability to absorb or reflect

Surface type

Albedo (%)

Fresh snow

95

Dark rock

10

Desert sand

35

Urban areas

12-18

Grassland and forest

10-25

Dry ploughed fields 10-12 Water

8

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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Latent and Sensible heat

Heat is redistributed over the Earths surface by three main processes

• • •

Latent Heat Flux Sensible Heat Flux Surface Heat Flux

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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Latent heat flux

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Conversion of solid and liquid water into vapour

• •

Circulation by the atmosphere

Needs a large amount of heat energy to break bonds in water

Condensation to rain or snow release stored energy

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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Sensible heat flux

Transfer of energy from surface to atmosphere by conduction and convection

• • •

Energy moved by advection from tropics to poles Creates atmospheric circulation Moves warm air to poles and cool air to tropics

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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere Surface heat flux

• • •

Energy transfered into tropical oceans from sun

Horizontal transfer of warm water (heat) from equator to poles and back again

Conversion of solar radiation to heat energy Conduction and convection transfer heat down water column

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Topic 3: Global Cycles and Physical Systems 3.1: The Atmosphere

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http://sciencebitz.com/wp-content/uploads/2008/04/atmosphere