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lesson 6 - Introduction In Our Atmosphere Global Climate...

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1 Introduction In Our Atmosphere & Global Climate Regions , you were introduced to how circulation in the atmosphere transfers energy around the globe. You learned the fundamentals of atmospheric pressure, pressure systems, variables that influence atmospheric air flow, and (general) global circulation patterns. If you recall, these general circulation patterns were the result of unequal global heating between the tropics and the polar regions. In this module, we are going to discuss atmospheric circulation in the tropics and an example of the way humans have adjusted to its seasonal variation. Our discussion on human response will concentrate primarily on the African Sahel . Why the Sahel, you ask? Take a guess. Global circulation Before exploring the details of this topic, let's review. General review Atmospheric motions are variable over space and through time, in that some motions occur over vast expanses of space (land or water) while others are very localized. Similarly, some motions occur unchanged for months or seasons, while others are very short-lived. General patterns of circulation arise, however, at a global scale. These patterns involve semi-permanent and predictable pressure and wind conditions and act as the preeminent mechanism for global heat redistribution. You should remember that four broad areas of pressure generally exist in the Northern and Southern Hemispheres. The Earth's general circulation is composed in part of a few, specific primary high- and low-pressure areas, which are highlighted for you on the figure below. You may notice that these areas exist as cells or bands of similar pressure and are often interrupted by landmasses. Secondary high- and low- pressure areas also exist, but we will talk about the importance of these areas in a bit. Major global pressure cells in July with equatorial low-pressure trough represented by the ITCZ dotted line (based on data from 1993).
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2 Between the major areas of pressure shown above, predictable wind patterns flow. Based on what you have already learned, in what direction do these winds flow? Considering both primary pressure areas and primary winds can help us to visualize a generalized model of global circulation. This list includes the seven surface components of circulation starting at poles and moving equatorward: Polar high-pressure cells (over N and S polar regions) Polar easterlies (poleward of 60° N and S latitude) Subpolar low-pressure cells (50° to 60° N and S latitude) Westerlies (35° to 60° N and S latitude) Subtropical high-pressure cells (STHs) (25° to 35° N and S latitude) Trade winds (between 25° N and S latitude) Equatorial low-pressure trough (the intertropical convergence zone (ITCZ)) (tropical) Generalized components of global atmospheric circulation .
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