Global air movements make steady winds called trade winds that blow all the time.

EQUATOR and TROPICS: Air from the mid-latitudes moves along the Earth's surface toward the equator to take the place of the air that rises there, making a loop of air movement called a Hadley cell. Air expands and rises at the equator and tropics because the sun heats that area the most.

THE POLES: The poles are cold because they do not receive a lot of heat from the sun. Therefore, air sinks down and moves away from the poles and rises again at about 60 degrees latitude.

EARTH'S ROTATION: The Earth is in constant motion turning from west to east. Since the Earth continually rotates, the trade winds are subject to the Coriolis force which affects wind direction. This means the winds—called geostropic winds—are deflected away from the rotation axis in a perpendicular direction. In other words, in the northern hemisphere, trade winds veer to the right. In the southern hemisphere, trade winds veer to the left.

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