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National Meteorological and Hydrological Services
Box 3.9 Technical Insight: How Weather and Climate Interact Although weather describes the short-term behavior of the atmosphere and climate describes the long-term average of the weather, no physical boundary separates them; the physical processes of the atmosphere, ocean, and land operate on a continuum in time and space. In reality, weather affects climate, and climate affects weather. Consider the following scientific insights: • Natural climate variations, such as the El Niño–Southern Oscillation and the North Atlantic Oscillation, significantly alter the intensity, track, and frequency of hazardous weather, such as extratropical and tropical cyclones and associated high-impact weather. • No longer-term regional variations exist, such as decadal variability in tropical cyclones and multidecadal drought in the Sahel region in Africa. • Conversely, small-scale processes have significant upscale effects on the evolution of large-scale circulation and the interactions among the components of the global system. For scientists, one big challenge is to better predict the spatial temporal continuum of the interactions between weather and climate, thereby bridging the gap between forecasting high-impact events at daily to seasonal time-scales. Another is to develop an integrated approach to improve how we predict this Earth system without making arbitrary distinctions that have no physical basis. Sources: Data from Brunet et al. 2010; Hurrell et al. 2009; Shapiro et al. 2010.
Box 3.10 Technical Insight: Using Radiosondes for Upper-Air Measurements Upper-air data are particularly useful and should ideally be obtained twice per day per station. The temperature, humidity, and wind profile is obtained by a radiosonde, which consists of an instrument package and balloon (hydrogen or helium filled). The balloon ascends to a height of about 20 kilometers. The instrument package is not recoverable, and the cost of each ascent is approximately US$280. Including the cost of a ground station (with a five-year lifetime), the annual indicative operating costs of running an upper-air station are about US$210,000 (Gray 2012). Because of the high cost of expendables, many developing countries struggle to maintain their upper-air networks without external support.
Numerical Weather Prediction (NWP) provides the basic guidance for weather forecasting beyond the first few hours (Kalnay 2003). Yet the human forecaster still has a critical role in interpreting the output and in reconciling sometimes conflicting information from different sources. This role is especially important in situations of locally severe weather. The capacity to use this information depend s on access to good-quality interactive workstations for overlaying and manipulating the basic information (photo 3.3). Weather forecasting offices produce a variety of forecast products, depending on their capability and users’ requirements. Many provide forecasts from 12 hours to seven days or longer. In modern NMHSs, forecasters spend most of Weather and Climate Resilience • http://dx.doi.org/10.1596/978-1-4648-0026-9