A case study on the genesis of a monsoon depression in the northern Bay of Bengal during Monsoon-77 experiment

Abstract

The collection of a short time series of upper air radiosonde, wind and upper ocean temperature data sets from the USSR four ship stationary polygon over the northern Bay of Bengal for the first time during 11-19 August 1977 afford & a unique opportunity to evaluate the hypothesis proposed by W. M. Gray on the genesis of a tropical cyclone for a monsoon depression which formed over the Head Bay on 19 August 1977. The product of six parameters (a) low level vorticity, (b) coriolis parameter, (c) inverse of the vertical shear of the horizontal wind from lower to upper troposphere, (d) ocean thermal energy of the top 60 m layer above 26 deg. C, (e) moist stability from surface to 500 mb (f) middle tropospheric relative humidity known as Gray's cyclogenesis parameter when modified suitably has also shown strong indications for the genesis of a monsoon depression which formed towards the end of the observational period in the neighbourhood of the polygon.