Climatological Characteristics and Structure of Tropical Cyclones


Vol NO: VOL. 14, ISSUE 86,

"Tropical cyclones (TCs) are intense low pressure systems where the wind speed in the surface circulation system exceeds 33 nautical miles per hour (knots). The low-pressure systems over the northern Indian Ocean (NIO) are classified (Table 1) on the basis of associated maximum sustained surface wind (MSW) at the surface level. Systems with the intensity of depressions and above are considered cyclonic disturbances. TCs occurring over the north Atlantic Ocean are known as hurricanes and those occurring over the Pacific are known as typhoons. A TC that has a MSW of 64 knots corresponds to a very severe cyclonic storm (VSCS) over the NIO. TCs occurring near the Australian continent are the willy-willies. Tropical cyclones usually do not occur over the south Atlantic Ocean or SE Pacific (east of 140oW) mainly because of the colder sea surface temperatures (SSTs) and other unfavourable ocean and atmospheric conditions.   Frequency About five to six TCs occur in a year over the NIO during the pre-monsoon (March-April-May) and post-monsoon (October-November-December) seasons. This accounts for about seven per cent of all global TCs. The ratio of formation over the Bay of Bengal (BoB) vis-à-vis the Arabian Sea (AS) is 4:1. Globally, the freque

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    Ajit Tyagi

    A tropical cyclone is an intense low pressure system that is classified on the basis of its wind speed. The phenomena has a definitive structure and a well-defined life cycle.

    "The author is Koteswaram Professor, Ministry of Earth Sciences, Air Vice Marshal (Retd) and Former Director General of India Meteorological Department."

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