The Hadley Cell involves air rising near the equator, flowing toward the North and South Poles, returning to the surface of the Earth in the subtropics, and flowing back toward the equator at the surface of the Earth. This produces winds called the trade winds and the tropical easterlies. Click on image for full size (114 Kb) Image courtesy of Tinka Sloss

The Hadley cell is an atmospheric circulation pattern in the tropics that produces winds called the tropical easterlies and the trade winds. In the Hadley cell, air rises up into the atmosphere at or near the equator, flows toward the poles above the surface of the Earth, returns to the Earth’s surface in the subtropics, and flows back towards the equator.

This flow of air occurs because the Sun heats air at the Earth’s surface near the equator. The warm air rises, creating a band of low pressure at the equator.  Once the rising air reaches the top of the troposphere at approximately 10-15 kilometers above the Earth’s surface, the air flows toward the north and south poles. The Hadley cell eventually returns air to the surface of the Earth in the subtropics, near 30 degrees north or south latitude.

Air near the surface flows toward the equator into the low pressure area, replacing the rising air. This area of low pressure and converging winds (air flowing together) is called the Intertropical Convergence Zone (ITCZ).  These winds are turned toward the west by the Coriolis effect and become the trade winds or the tropical easterlies.

The air that returns back to the surface of the Earth in the subtropics produces a band of high pressure called the subtropical high. Once the air reaches the surface, some air flows toward the equator from the subtropical high to the lower pressure in the ITCZ to become part of the trade winds.