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the year
MonthlyMeanTemperatures(http://upload.wikimedia.org/wikipedia/commons/b/b3/
MonthlyMeanT.gif)
From all this information you can understand why the tropics are warmer than the polar
areas. The temperate regions are in between, both in latitude and average air temperature.
The air in Earth’s atmosphere moves as the Sun warms some areas more than others. The
main reason we have different climates at various latitudes is also determined by the amount
of sunlight that hits each place (Figure17.1).
Figure 17.1: This map of annual average temperatures shows how dramatically temperature
decreases from the low latitudes to the high latitudes. ( 21 )
Prevailing Winds
There are winds that usually blow in one particular direction, called the global wind belts.
These winds are called the trade winds, the westerlies and the polar easterlies. The direction
these winds blow is different at various latitudes. In the Earth’s Atmosphere chapter, you
learned that air rises at low pressure areas, which form at 0oand again at 50oto 60onorth
and south of the equator. Air sinks at high pressure areas, which form at around 30oN and
S and at the poles. These low and high pressure zones represent the upward and downward
flowing regions of the Hadley, Ferrell and Polar atmospheric circulation cells (Figure17.2).
Low pressure areas form where air is moving upwards or rising. High pressure areas form
where cooler, drier air sinks. Areas of high pressure often have climates that are cooler and