Cyclone From Wikipedia, the free encyclopedia Jump to: navigation , searchThis article is about the meteoro logi cal pheno menon. For other uses, see Cyclone (disambiguation) . Polar low over the Barents Sea on February 27, 1987 In meteorology , a cyclone is an area of closed, circular fluid motion rotating in the same direction as the Earth. [1][2] This is usually characterized by inward spiralingwinds that rotate counter clockwise in theNorthern Hemisphere and clockwise in the Southern Hemisphere of the Earth. Most large-scale cyclonic circulations are centered on areas oflow atmospheric pressure. [3][4] The largest low-pressure systems are cold-core polar cyclones and extratropical cyclones which lie on the synoptic scale. Warm-core c ycl ones such a s tropical cyclones, mesocyclones , and polar lows lie within the smallermesoscale . Subtropical cyclones are ofintermediate size. [5][6] Upper level cyclones can exist without the presence of a surface low, and can pinch off from the base o f the Tropical Upper Tropospheric Trough during the summermonths in the Northern Hemisphere. Cyclones have also been seen on other planets outside ofthe Earth, such as Mars andNeptune. [7][8] Cyclogenesis describes the process o f cyclone formation and intensification. [9] Extratropical cyclones form as waves in large regions of enhanced mi dlatitude temperature contrasts ca lled baroclinic zones . These zones contract to form weather fronts as the cyclonic circulation closes and intensifies. Later in their life cycle, cyc lones occlude as cold core systems. A cyclone's trackis guided over the course of its 2 to 6 day life cycle by the steering flow of the cancer orsubtropicaljet stream. Weather fronts separate two masses of airof different densities and are associated with the most prominent meteorological phenomena . Air masses separated by a front may differ in temperatureorhumidity . Strong cold fronts typically feature narrow bands ofthunderstorms and severe weather, and may on occasion be preceded by squall lines ordry lines. They form west of the
