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Three-cell Circulation model - Coggle Diagram
Three-cell Circulation model
Three-cell circulation model
Convection cells are separated by pressure belts, bands of high pressure and low pressure found about every 30o of latitude.
Air travels in many large, circular patterns called convection cells.
According to the three-cell circulation model, in each hemisphere,
atmospheric circulation cells are located between
the equator and 30o altitude, 30o and 60o altitude, and 60o altitude and the pole.
As warm air rises over the equator and moves towards the poles, the air begins to cool. At about 30° north and 30° south latitude, some of the cool air begins to sink. Cool sinking air causes high pressure belts near 30° north and 30° south latitude.
The cool air flows back to the equator where it warms and rises again
.
At the poles, cold air sinks and moves towards the equator. Air warms as it moves away from the poles. Around 60° north and 60° south latitude, the warmer air rises creating a low pressure belt.
The warmer air flows back to the poles
.
Global winds
The combination of convection cells found every 30° of latitude, and the Coriolis effect produce patterns of circulation called
global winds.
The wind belts that extend from the poles to 60° latitude in both hemispheres are called the
polar easterlies
.
The polar easterlies are formed as cold, sinking air moves from the poles toward 60° north and 60° south latitude.
In the Northern Hemisphere, polar easterlies can carry cold arctic air over the United States, producing snow and freezing weather.
The wind belts found between 30° and 60° latitude in both hemispheres are called the
prevailing westerlies
.
The westerlies flow toward the poles from west to east.
The westerlies can carry moist air over the United States, producing rain and snow.
In both hemispheres, the winds blowing from 30° latitude almost to the equator are called
trade winds
.
The Coriolis Effect causes the trade winds to curve to the west in the Northern Hemisphere and to the east in the Southern Hemisphere.
Calm regions
The air usually stays calm in high pressure and low pressure regions.
Winds are light, and they often change direction.
The trade winds of the Northern and Southern Hemispheres meet in an area around the equator called the
doldrums
. In the doldrums, there is very little wind because the warm, rising air creates a region of low pressure.
At about 30° north and 30° south latitude, sinking air creates a region of high pressure. The winds at these locations are weak. These regions are called the
horse latitudes
.