process

Hadley cell

A large-scale atmospheric circulation in the tropics with rising air near the equator and sinking in the subtropics.
10 related articles

Description

The Hadley cell is a large-scale pattern of atmospheric circulation in the tropics, characterized by warm air rising near the equator, flowing poleward at high altitude, cooling and sinking in the subtropics (around 20–30° latitude), and then returning toward the equator near the surface. This circulation is a fundamental driver of tropical weather and climate, shaping rainfall patterns, trade winds, and the location of deserts. It is named after George Hadley, who proposed the basic idea in 1735 to explain the trade winds.

History

George Hadley first described the circulation in 1735, though his model was later refined in the 19th and 20th centuries by meteorologists who incorporated the effects of Earth's rotation and angular momentum conservation.

How it works

Intense solar heating at the equator warms the air near the surface, causing it to expand and rise, creating a zone of low pressure and heavy precipitation (the Intertropical Convergence Zone). As the air rises, it cools and loses moisture through rain, then spreads poleward in the upper troposphere. At subtropical latitudes, the now-dry air sinks, creating high-pressure zones and clear skies—this is why many of the world's deserts, like the Sahara, lie near these latitudes. The sinking air then flows back toward the equator at the surface, deflected by the Coriolis effect into the easterly trade winds.

In practice

Understanding the Hadley cell is essential for seasonal weather forecasting, predicting monsoon patterns, and projecting how climate change may shift tropical rain belts and expand subtropical dry zones.

Fun fact

The Hadley cell is expanding poleward at about 0.5–1 degree of latitude per decade due to climate change, which is shifting desert boundaries and altering weather patterns in regions like the Mediterranean and southern Australia.

Concept graph →

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