The three cell model

Hadley cells, 0-30° latitude

  • Solar heating at the equator warms the air above.
  • The air rises and expands creating low pressure.
  • The air travels to around 30°, cooling as it moves.
  • At around 30° the cooled air sinks back to Earth to create an area of high pressure.
  • Air moves from this high-pressure area to the equatorial low-pressure area.
  • This is a thermally direct cell.

Polar cells, 60-90° latitude

  • The air above the poles is cold.
  • The cold air sinks creating high pressure.
  • The air moves towards the equatorial low-pressure zone, and warms up when it meets the land or ocean.
  • At around 60° this warmed air rises.
  • This is another thermally direct cell.

Ferrel cells, 60-30° latitude

  • The Ferrel cells are found between the Hadley and Polar cells.
  • Cold air sinks near 30° and rises near 60°. The air at the Earth's surface flows northwards and is affected by the Coriolis force.
  • The Ferrel cell is thermally indirect.
The Hadley cells occur next to the equator. The Polar cells occur next to the North and South Poles. In between the two are the Ferrel cells.Global circulation cells

Jet streams

These are very strong and fast-moving meandering wind bands. They are found at high altitudes, just below the tropopause, where the circulation cells meet. Jet streams are caused by pressure differences in the upper atmosphere and they move the weather systems around the planet.