Atmospheric Circulation

Hadley Cells

The Hadley Cell is the beginning of the journey for the warm, moist air in Equatorial regions. The air first rises near the Equator in huge cumulus clouds, then travels poleward at very high altitudes, then sinks near 30 degrees North and South, and finally returns Equator-ward at the Earth's surface.

Let's following a parcel of air through this cycle.

1) Convective towers in the Tropics

At the Equator, warm, moist air is unstable and rises all the way to the top of the troposphere. The top of the troposphere is called the tropopause and is about 10 to 11 miles (about 17,000 m) high in the tropics. The rising air results in a broad area of low surface pressure. The surface winds are light, the weather can be monotonous, and the region is referred to as the "doldrums."

As the warm, moist air rises, water vapor condenses and forms huge cumulus towers. The condensing water vapor releases latent heat, which supplies energy for the circulating air.



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