The Hadley cell mechanism is well understood. The atmospheric circulation pattern that George Hadley described to provide an explanation for the trade winds matches observations very well. It is a closed circulation loop, which begins at the equator with warm, moist air lifted aloft in equatorial low pressure areas (the Intertropical Convergence Zone, ITCZ) to the tropopause and carried poleward. At about 30°N/S latitude, it descends in a high pressure area. Some of the descending air travels equatorially along the surface, closing the loop of the Hadley cell and creating the Trade Winds.
Though the Hadley cell is described as lying on the equator, it is more accurate to describe it as following the sun’s zenith point, or what is termed the "thermal equator," which undergoes a semiannual north-south migration.
Read more about this topic: Atmospheric Circulation, Latitudinal Circulation Features
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