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Precipitation patterns are linked to temperature, since more water
evaporates from the ocean surface when its temperature is higher.
This water vapor condenses as clouds and then rain, hail or snow.
Maximum rainfall, therefore is around the equatorial zone, with
the poles actually receiving very little snowfall. Areas which receive
low rainfall throughout the year are deserts and the lack of cloud
cover makes some of them the hottest areas of the world.
The band of high equatorial rainfall moves north and south with
the seasons and marks the boundary between northern and southern
atmospheric circulation - called the inter-tropical convergence
zone. The cycle of rainfall has more meaning within the tropics
than the variation of temperature, with rainy and dry seasons
determined by latitude, adjacent ocean currents and topography.
The monsoon cycle of southern Asia is reinforced over India by
a reversal of currents and airflow from the Indian Ocean, producing
a pronounced rainfall maximum in July-August.
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