The Coriolis force causes the simple solar-driven Hadley circulation on Earth to break up into three smaller circulating systems or cells. The cell nearest the Equator is called the Hadley cell, in which air rises near the equator, flows north or south, and sinks again near a latitude of 30° in both hemispheres. Returning air near the surface is deflected westward by the Coriolis force, causing the so-called trade winds. In the cells nearest the poles, the Polar cells, air sinks at the poles, flows outward along the surface, rises near latitude 60° in both hemispheres, and flows back to the poles at high altitudes. A very weak cell, called the Ferrel cell, occurs between the Hadley and Polar cells. Here, air rises near latitudes of 60°, flows equatorward at high altitudes, and sinks near latitudes of 30°. Returning air near the surface is deflected westward, forming the so-called prevailing westerlies.
The Coriolis force also affects air flow on a smaller scale. As air flows out of areas of high pressure in both hemispheres, they are turned to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. The result is a clockwise flow around the Northern Hemisphere high and a counterclockwise flow around the Southern Hemisphere subtropical high.
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