K Muni Krishna and S Ramalingeswara Rao
Keywords: Summer monsoon, rainfall, circulation, latent heat flux.
Abstract: The decadal variations of all India summer monsoon seasonal rainfall during 1871-2000 are studied. Two extreme decades, one positive (1951-60) and another negative (1981- 1990) in the recent decades are considered depending upon the values of all-India monsoon seasonal rainfall. For these two decades, the synoptic features are studied for the parameters like mean seasonal values of air temperatures, zonal wind and meridional wind at two levels, 850hPa and 150hPa and latent heat flux in domain of 30oE-120oE and 30oS-40oN. The frequency of Bay of Bengal cyclonic systems during June through September is also studied. During good (poor) monsoon decade there is an enhancement (a reduction) in the intensity of easterly jet and frequency of Bay of Bengal cyclonic systems during June through September. It is also observed that the strength of the monsoon trough is pronounced/reduced during active/poor monsoon situations. Bay of Bengal and Arabian Sea play an important role in transporting moisture towards Indian main land and deciding the behaviour of Indian summer monsoon.
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