Some features of a tropical depression over the Arabian Sea during the onset of the southwest monsoon during Monex 1979

Abstract

During the onset phase of the southwest monsoon, occasionally, deep depressions/cyclonic storms form over the Arabian Sea. Some aspects of formation and structure of a tropical depression which formed over the Arabian Sea have been studied based on extensive data. The relative vorticity, divergence, thermal and moisture fields for the system have been analysed. This study revealed the existence of the following main characteristics of the tropical depression/storm: (a) the depression developed from the middle level vortex; (b) the shear vorticity of the low level westerly jet, cumulus convection and low vertical wind shear played significant role in its development, (c) cyclonic vorticity maximum in the middle level, (d) convergence maximum in the forward sector to the west of the storm centre, (e) level of non-divergence around 700 mb, (f) lowest temperature in the southwest sector and highest temperature in the northern sector in the lowest troposphere and (g) moisture maximum around the storm centre upto middle troposphere.