Upwelling Off the Southwest Coast of India

Various factors r esponsible in inducing upwelling are discussed. A distinction is m a de between the process of upwelling: and its etlects On the environmental cOnditions. Upwelling oft' the southwest coast of India is discussed in relation °to the time variation of density structure (CSt), horizontal divergence of surface CUrrent vectors, wind stress components parallel and perpendicular to the COast, thermal structure and sea level. U pwelling In this r egion comm ences in the deeper layers of about 90 m in March a nd the upwelled water reaches the surface by May. The process continues to occur vigorously till June. From then, with the increase in strength of southwest winds, intensity of upwelling reduces and finally ceases to be present by July/August when the onshore winds of the southwest monsoon have maximum strength. Th~ r everse process, sinking, sets in by September. Ve rtical velocity, i.e. upwelling, calculated (1) from the ve r tical shift of the isopycnal with time and (ii) from the a verage horizontal divergence, is 1·5 X 10-s and 1·8 x 10-s em sec-I respectively.