Hydrographic characteristics of central Bay of Bengal waters during southwest monsoon of 1983

Abstract

During cruises 120 and 124 of R V Gaveshani two sections, viz. Visakhapatnam - Port Blair and Madras - Port Blair, in Bay of Bengal have been covered twice. The sea surface temperature (SST) shows a decrease of about 2 degrees C from premonsoon to postmonsoon. The loss of energy from the sea surface to the atmosphere by evaporational cooling due to strong monsoonal winds and reduction in the incoming solar radiation by clouds may result in a net loss of energy (cooling). During premonsoon the isotherms off Visakhapatnam show an upward slope towards the coast resulting from the Ekman drift, forcing the cooler denser subsurface water to come up under a northerly flow. However, the isothermal pattern during postmonsoon reveals the possibility of a thermal adjustment within the water column by way of advection as manifested by stretching of isotherms. Distribution of relative velocities along the sections indicates the presence of gyres (zones of convergence and divergence). There appears a remarkable variation of these gyral systems from premonsoon to postmonsoon