Atmospheric Circulation

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Atmospheric Circulation
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• The Earths energy is partly redistributed by
  atmospheric circulation.
• Factors in the Cirulation of Air include
• Pressure Gradient Force
• Coriolis Force
• Rossby Waves and Jet Streams

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• Pressure Gradient Force
• The pressure gradient is the difference in air
  pressure between 2 places on the earths surface.
• Air is pushed out of areas with high pressure
  towards areas with low pressure, where it rises.
  This is the pressure gradient force.
• The pressure gradient force is the main mechanism
  for heat energy moving from the Tropics towards
  the Poles.

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High Pressure
Low Pressure
Earth
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• Coriolis Force
• The Earth is spinning from West to East, but the
  atmosphere is not.
• Winds appear to be deflected, so they dont blow
  directly from high to low pressure, but
  diagonally instead this is the Coriolis Force.
• The Coriolis Force is zero at the Equator but
  increases towards the Poles, so winds are
  deflected more and more as they move to the
  Poles, but the opposite as they head to the
  Equator.

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The amount of deflection is reduced by friction
with the Earths surface, so winds next to the
surface are deflected only a little. Winds in
the upper atmosphere are not affected by friction
and are deflected so much that they blow parallel
to the isobars these winds are called
geostrophic winds. The Coriolis force reduces
the amount of heat energy moving from the Tropics
to the Poles, because in the upper atmosphere,
some air is deflected so much that it does not
move polewards at all.
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• Rossby Waves and Jet Streams
• Rossby waves are belts of fast flowing westerly
  winds in the upper atmosphere and move in a
  wave-like patter.
• Jet Streams are narrow bands of very fast flowing
  air within the Rossby waves.
• There are 2 jet streams in each hemisphere
• 1) The Polar Front jet stream
• 2) The Sub-Tropical jet stream
• Rossby waves and jet streams play a small part in
  the redistribution of heat energy.

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Atmospheric Circulation

• Air does not simply move from the Tropics to the
  Poles and back again in a single cell.
• There are in fact 3 circulation cells
• The Hadely Cell
• The Ferrel Cell
• The Polar Cell

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Polar Highs
H
90
Mid-Latitude Lows
60
L
H
30
Horse Highs
Equatorial Low
L
0
H
30
L
60
H
90