Atmospheric Circulation

The Earth’s energy is partly redistributed by atmospheric circulation. 1.Factors in the Cirulation of Air include; Pressure Gradient Force Coriolis Force Rossby Waves and Jet Streams

Pressure Gradient Force The pressure gradient is the difference in air pressure between 2 places on the earth’s 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.

Earth High Pressure Low Pressure

Coriolis Force The Earth is spinning from West to East, but the atmosphere is not. Winds appear to be deflected, so they don’t 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.

The amount of deflection is reduced by friction with the Earth’s 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.

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.

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; 1.The Hadely Cell 2.The Ferrel Cell 3.The Polar Cell

L H L H H L H Polar Highs Mid-Latitude Lows Horse Highs Equatorial Low