The Intertropical Convergence Zone is a band of upwelling moist air near the equator. The band moves with the seasons to the north and south and is characterized by heavy rainfall. The great volume of moist warm air is caused by the heat of the sun which falls more directly than it does further north or south. Great quantities of water vapor are evaporated from the oceans and other water bodies as well as from tropical vegetation. As warm water vapor is lighter than the air above it, it rises, by convection, until it grows cool enough that it condenses and falls as precipitation. The air is then pushed either to the south or north by the rising moist air below it. Meanwhile, at the surface the ascending air is pulling cool dry air in from the north and south. This circulation pattern, which circles the globe, is called a Hadley cell. The circulation is not simply in the north-south plane, but has a strong westerly component, the return flow being the trade winds which collect water by evaporation.
If air circulation patterns, either to the north or south of the Zone, pull moist air towards the pole, a monsoon may occur, as is regularly the case in the summer in the subcontinent of India. This is generally associated with a continental high pressure area which on its western side circulates to the north or northeast. or in the southern hemisphere to the south or southeast.
In 2007, above average rain associated with the zone occurred in Africa, resulting in flooding and breaking an extended drought. This occurrence may be associated with increased evaporation due to global warming, or not...
- Satellite image of the Intertropical Convergence Zone on Earth Observatory
- The Wikipedia article, "Intertropical Convergence Zone
- The Wikipedia article "Monsoon trough"
- Heavy rains in Africa during 2007 Image made with data collected by the Tropical Rainfall Measuring Mission.
Adapted from the WaterWiki article "Intertropical convergence zone" http://water.wikia.com/index.php?title=Intertropical_convergence_zone&oldid=3275
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