What is global atmospheric circulation?
The
air across the planet moves in a specific way. This movement starts at
the equator, the hottest part of the Earth. Due to high temperatures at
the equator, the air rises up into the atmosphere. This creates low
pressure (as the air is rising it puts less pressure on the Earth’s
surface). As the air rises it becomes colder, causing condensation
(forming clouds) that leads to rainfall. This is why tropical
rainforests are found along the equator!
Global atmospheric circulation model
When the air reaches the top of the atmosphere it needs somewhere to
go. Some of the air travels north and some south of the equator. The air
cools and then sinks at around 30° north and south of the equator. As
the air is sinking this creates high pressure. As moisture in the
sinking air fell at the equator it is dry so few clouds form here. This
is why deserts are found along 30° north and south of the equator.
The movement of air between the equator and 30° north and south is
known as the Hadley Cell. Air rises again at around 60° north and south
and descends again around 90° north and south forming the Ferrel and
Polar Cell.
Global atmospheric circulation creates winds across the planet as air
moves from areas of high pressure to areas of low pressure. It also
leads to areas of high rainfall, like the tropical rainforests, and
areas of dry air, like deserts
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