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| Asked by:
Anonymous on May-06-2008 04:49:41 | |
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| Answer
1 Contributor: prophetess on May-08-2008 09:31:54 |
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In meteorology, a cyclone is an area of low atmospheric pressure characterized by inward spiraling winds that rotate counter clockwise in the northern hemisphere and clockwise in the southern hemisphere of the Earth. The generic term covers a wide variety of meteorological phenomena. These include tropical cyclones and extratropical cyclones, so meteorologists rarely use "cyclone" without additional qualification.
There are a number of structural characteristics common to all cyclones. Their center is the area of lowest atmospheric pressure, often known in mature tropical and subtropical cyclones as the eye. Near the center, the pressure gradient force (from the pressure in the center of the cyclone compared to the pressure outside the cyclone) and the Coriolis force must be in an approximate balance, or the cyclone would collapse on itself as a result of the difference in pressure. The wind flow around a large cyclone is counterclockwise in the northern hemisphere and clockwise in the southern hemisphere as a result of the Coriolis effect. (An anticyclone, on the other hand, rotates clockwise in the northern hemisphere, and counterclockwise in the southern hemisphere.)
Cold-core cyclones (most cyclone varieties) form due to the nearby presence of an upper level trough, which increases divergence over an area that induces upward motion and surface low pressure. Warm-core cyclones (such as tropical cyclones and many mesocyclones) can have their initial start due to a nearby upper trough, but after formation of the initial disturbance, depend upon a storm-relative upper level high to maintain or increase their strength.
Each of the six main types of cyclone has further characteristics which define it as either a Polar cyclone, Polar low, Extratropical, Subtropical, Tropical, or Mesoscale. |  Report
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