VIEW: Convection Cells
Convection Cells
Within the troposphere are convection cells. Air heated at the ground rises, creating a low pressure zone. Air from the surrounding area is sucked into the space left by the rising air. Air flows horizontally at top of the troposphere; horizontal flow is called advection. The air cools until it descends. When the air reaches the ground, it creates a high pressure zone. Air flowing from areas of high pressure to low pressure creates winds. The greater the pressure difference between the two pressure zones, the faster the wind blows.
Warm air rises, creating a low pressure zone; cool air sinks, creating a high pressure zone. Image courtesy of CK-12.
Because more solar energy hits the equator, the air warms and forms a low pressure zone. At the top of the troposphere, half moves towards the north pole and half toward the south pole. As it moves along the top of the troposphere it cools. The cool air is dense, and when it reaches a high pressure zone it sinks to the ground. The air is sucked back toward the low pressure at the equator. This describes the convection cells north and south of the equator.
There are two more convection cells in the Northern Hemisphere. The Ferrell cell is between 30oN and 50o to 60oN. This cell shares its southern, descending side with the Hadley cell to its south. Its northern rising limb is shared with the Polar cell located between 50oN to 60oN and the North Pole, where cold air descends.
There are three mirror image circulation cells in the Southern Hemisphere. In that hemisphere, the Coriolis effect makes objects appear to deflect to the left. The total number of atmospheric circulation cells around the globe is six.
Source: Circulation in the Atmosphere. Retrieved from http://www.ck12.org/book/CK-12-Earth-Science-Concepts-For-High-School/r16/section/9.15/ on August 26, 2013.
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