Characteristic features of monsoon depression of the Bay of Bengal – An observational study

Abstract

The present study deals with three aspects of Bay of Bengal depressions during the monsoon period (i) to trace the possible origin of the disturbances, (ii) vertical structure during the formative, mature and decaying stages, and (iii) examination of the inter-relation between the intensification of depressions in the Bay and the strengthening of the lower tropospheric westerly jet and tropospheric upper level easterly jet. In all, 64 cases of monsoon depressions which formed in the decade from 1970 to 1979 have been studied.

It is observed that (i) 82 per cent of the total number of the systems advected either from east or southeast, (ii) the tilt of the circulation with height, was in the direction from which the systems advected in the formative stage. In the mature stage, there was practically no tilt and during the dissipating stage, no well-defined pattern was observed and (iii) the lower level westerly jet strengthened 1-2 days prior to the maximum intensification in about 55 per cent cases, whereas the strengthening of upper level easterly jet and maximum intensification were simultaneous in about 75 per cent of the total number of the cases.