Governing Factors Associated with Intensification of TC-A Diagnostic Study of VSCS PHAILIN and LEHAR

Tropical cyclones (TCs) are synoptic scale intense low pressure systems which form over the warm tropical oceans characterised by strong cyclonic winds and organised convection with heavy rainfall. The TC causes enormous damage to life and property at the time of crossing the coast and subsequent movement over the land. The TCs can impact over a wide area with its strong winds, heavy rains and storm surges. Gray (Hurricanes: their formation structure and likely role in the tropical circulation. In: Shaw DB (ed) Meteorology over the Tropical Oceans. Royal Meteorological Society, Bracknell, pp 155–218,1979) prepared a detailed climatology of the TCs in the global ocean basins. He observed that annually about 80 TCs form globally of which half to two thirds reach hurricane strength (maximum sustained winds greater than 33 m/s). East coast of India is frequently affected by TCs that form over Bay of Bengal (Tyagi et al., Inter-annual variation of frequency of cyclonic disturbances landfalling over WMO/ESCAP Panel Member Countries. WMO/TD-No. 1541 on 1st WMO International conference on Indian Ocean tropical cyclones and climate change, Muscat, Sultanate of Oman, 8–11 March 2009, WWRP-2010/2, 2010). During the period 1891–2010, about 134 severe TCs crossed the east coast of India (IMD, Cyclone e-Atlas-IMD tracks of cyclones and depressions over North Indian Ocean. www.​rmcchennaieatlas​.​tn.​nic.​in, 2011; Atlas of storm track). Anthes (Tropical cyclones: their evolution, structure and effects. Meteorological Monographs, American Meteorological Society, Boston, 1982) has extensively studied the three dimensional structure of TC. He observed that the surface pressure is lowest at the centre of the TC and increases outward. The wind speed reaches its maximum value at nearly 40–80 km from the centre beyond which it decreases. The central parts are warmer than the surroundings and the temperature anomaly could be more than 10° K at the upper troposphere. The TC grows upto a height of 10–15 km. Intense TCs frequently develop an eye, which is a cloud free region at the centre of the storm characterised by the presence of subsidence.