global atmospheric circulation

• low pressure is when the air rises as the air is no longer pushing down on the earth , leading to less pleasant weather.
• high pressure is when air sinks and pushing on to the earth, bringing clear skies as the air cannot rise to form clouds.
• convection cells:

  the air moves in 3 convection cells:

  • polar cells are found between 90-60 degrees latitude.
  • the ferrel at 60-30 degrees latitude
  • the hadley at 30-0 degrees latitude.
  • convection cells are areas where warm air rises and cool air sinks in cycle.
• hadley cells

  air rises at the equator because it is hot, so it is less dense

  this creates low pressure so clouds can form (rainforests).

  the air then spreads out and moves away from the equator, sinking and cooling at 30 degrees n/s of the equator.

  this creates a high pressure zone so there's less rainfall as the air is sinking and not rising (eg: deserts).
• ferrel cells

  • air from the hadley cell moves poleward and begins to cool
  • this cooling causes the air to become denser + sink , leading to high pressure.
  • simultaneously, in the ferrel cell, air from the polar cell moves towards the equator + begins to warm
  • this warming causes the air to become less dense and rise = low pressure
  • the area of lower pressure is responsible for the wet climate of the UK as it provides optimal conditions for cloud formation.
• polar cells

  air sinks at the poles because it's cold, so it's dense.

  this creates high pressure so cloud formation is inhibited. therefore cold and dry areas are established.

  the air then circulates closer to the ferrel cell where it warms.