The Coriolis Effect provides a general wind pattern in belts. The
rising moist air at the equator creates a series of low pressure zones
along the equator. Water vapor in the moist air rising at the equator
condenses as it rises and cools causing clouds to form and rain to fall.
After this air has lost its moisture, it spreads to the north and south,
continuing to cool, where it then descends at the mid-latitudes
Descending air creates zones of high pressure, known as subtropical
high pressure areas. Because of the rotating Earth, these descending
zones of high pressure veer in a clockwise direction in the northern
hemisphere, creating winds that circulate clockwise about the high
pressure areas, and giving rise to winds that blow from the northeast
back toward the equator. These northeast winds are called the trade
winds. In the southern hemisphere the air circulating around a high
pressure center moves toward the left, causing circulation in a
counterclockwise direction, and giving rise to the southeast trade winds
blowing toward the equator.