6 The Global Wind System

Hadley Cells

Hot Equator → Air Rises → Sinks at 30°

• Found between 0° and 30° latitude.

• Warm, moist air rises at the equator → low pressure.

• Air moves poleward high up, then cools and sinks at 30° → high pressure.

• Surface winds blow back towards the equator as Trade Winds.

Ferrel Cells

Middle Cell → Westerlies

• Found between 30° and 60° latitude.

• Driven by the Hadley and Polar Cells.

• Surface winds blow towards the poles.

• These winds are called the Westerlies.

Polar Cells

Cold Poles → Air Sinks → Flows Out

• Found between 60° and 90° latitude (the poles).

• Cold, dense air sinks at the poles → high pressure.

• Air flows towards the equator at the surface.

• It eventually rises and returns poleward higher up.

• Surface winds are called Polar Easterlies.

Annotated Sketch Tip

Use a blue pen to indicate cold air masses and sinking air, and a red pen to indicate warm air masses and rising air.

Show the direction of air movement at the surface and at high altitudes for each cell.

Indicate the prevailing wind belts (Trade Winds, Westerlies, Polar Easterlies).