Weather Whys; Circulation Cells

This is Weatherwise. Meteorologists describe three large weather circulation patterns or cell in each hemisphere. They are known as the Hadley, the Ferrel, and the polar cells. In the northern hemisphere, the Hadley cell has warm air arising at the equator, moving northward and sinking at about 30 degrees north latitude. The Ferrel cell also has sinking air at 30 degrees, which moves northward along the ground and rises at 60 degrees north. Interestingly enough, the sinking air of the Ferrel and Hadley cells is partially responsible for many of the major deserts on Earth. The Sahara has been impacted by that air, as have the southwestern United States and northern Mexico. The Saudi desert and Kuwait are in the affected region as well. Large areas of constantly descending air over a location mean almost no rain will occur there. That calm pattern also meant trouble for mariners in the days when they relied on the

wind to move their ships. In fact, a particularly unfortunate crew might be stuck without a breeze for weeks. The latitudes 30 degrees north and south of the equator are known as the horse latitudes, trapped sailors often had to throw their horses overboard when they ran out of fodder. But the Hadley cell has a lot to do with the world's major rain forests too. The warm, moist air, which rises at the equator, helps produce a lot of rain in the equatorial belt. As a result, parts of the Brazilian rain forest and equatorial Africa may receive more than a hundred inches of rain per year. We'd like to know what you think of Weatherwise, please write to us at Weatherwise, KGOU Radio, the University of Oklahoma, Norman, Oklahoma, 73019-025O. Weatherwise is made possible by a grant from the National Science Foundation. I'm creambottom.