Tropical Cyclone Wind Threat for the Bay of Bengal

摘要

The problem in the Bay of Bengal is partly attributable to the distribution of population in low lying and unprotected areas along the bay, but more important is the configuration of the bay which results in large cyclone induced storm surges (often incorrectly referred to as tidal waves). These surges are an elevation of the sea surface because of the 'barometer effect' (pushing up the water into the cyclones central low pressure) combined with the buildup of wind driven water along the coast. These are superimposed on the astronomical tides which have a 12-hourly period (two highs and two lows per day) and a large tidal range at least with some combinations of the solar-lunar cycles. An unfortunate coincidence of a large storm surge and high tide can increase the mean water level by several meters, thus inundating large coastal areas with devastating effects. Forecast errors have gradually been reduced over the past few decades, but still they persist and their reduction seems to have leveled off in the decade of the seventies (Jarrell et al 1978, Neumann 1978). The improvement was most pronounced in the regions of the world where observation improved. This was mostly post WWII aircraft reconnaissance supplemented increasingly after 1964 by meteorological satellites. In the Bay of Bengal the satellite era is just emerging, thus we may expect to see improvement in forecasting capability there. The aim of this research was to develop a reliable estimate of the probability of 40, 65 and 100 kt winds for points under threat of a tropical cyclone.