Hadley cell, Ferrel cell, Polar cell | Atmospheric circulation

Air circulates in the atmosphere forming six different cells, three in each hemisphere. These cells are- Hadley cell, Ferrel cell, and Polar cell.

Hadley cell

Hadley cell
  • The equator receives more heat as compared to other regions. As a result, the air at the equator becomes warm and moist (warm air holds more moisture than cold air).
  • This warm and moist air rises and thus cools giving up moisture and leading to the formation of thunderstorm clouds which bring rain at the equator.
  • A low-pressure area is created at the equator which makes the air at the surface in the tropical zone move towards the equator.
  • The air rises at the equator till near tropopause (10-15 km) and then moves towards the poles on either side of the equator.
  • As the air moves towards the poles it cools to an extent and collides with a colder air mass coming from the poles and sinks.
  • This happens at about 30 degrees latitude and a high-pressure zone is created.
  • The sinking air is forced to move towards the equator. This is because the general flow of air is from high pressure to low pressure.
  • As the air moves towards the equator, it deviates towards the west due to the Coriolis force. This gives rise to the trade winds or Easterlies of the tropics.
Trade winds
Coriolis force

Ferrel cell

  • Air in the ferrel cell move towards the poles near the surface. This is a part of sinking air mass at 30 degree latitude.
  • At about 60 degree latitude, this air mass collides with another air mass coming from the poles.
  • The air rises after collision and returns at 30 degree latitude to complete the ferrel cell.
  • The westerly winds are found near the surface in the ferrel cell due to coriolis force.

Polar cell

  • Polar cell is the smallest and the weakest cell.
  • The cold air from the poles (near the surface) move towards the lower latitudes and interacts with the ferrel cell.
  • The air rises after interaction and returns to sink at the poles again. Thus completing the polar cell.

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