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What is an anticyclone?
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| An anti-cyclone is a large atmospheric circulation system with the
wind flowing clockwise
within it in the Northern Hemisphere, and counter-clockwise in the Southern Hemisphere. It is
associated with relatively high pressure at the surface and in the lower troposphere.
Anticyclones usually form when an airmass is cooled over a cool ocean surface, or over
land during the fall, winter, or spring when little sunlight is available.
The cooling causes the air
mass to shrink vertically, becoming slightly thinner. This shrinkage then causes surrounding air in the upper troposphere to fill up the extra space. The
added weight of the extra air causes higher pressure at the surface. The higher pressure air at the surface then
tries to flow outward toward lower pressure, but as it does, the rotation of the Earth turns the wind to the right (in
the Northern Hemisphere, to the left in the Southern Hemisphere), resulting in the clockwise wind flow around
the high pressure.
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| Interesting facts:
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| The strongest anticyclones occur over Asia and North America in the winter when
clear air and little sunlight causes the formation of large cold air masses.
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