Holton, James R. Department of Atmospheric Sciences, University of Washington, Seattle, Washington.
Last reviewed:January 2020
- Extratropical cyclones
- Tropical cyclones
- Related Primary Literature
- Additional Reading
A vortex in which the sense of rotation of the wind about the local vertical is the same as that of the Earth's rotation. Thus, a cyclone rotates clockwise in the Southern Hemisphere and counterclockwise in the Northern Hemisphere. In meteorology the term cyclone is reserved for circulation systems with horizontal dimensions of hundreds of kilometers (tropical cyclones) or thousands of kilometers (extratropical cyclones). For such systems the Coriolis force due to the Earth's rotation and the centrifugal force due to flow curvature are both directed to the right of the direction of the flow. Away from the surface of the Earth these two forces are approximately balanced by the pressure gradient force, which is directed toward low pressure (Fig. 1), so that there must be a pressure minimum at the center of the cyclone, and cyclones are sometimes simply called lows.
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