On interactions between the Southwest Monsoon Current and the Sea Surface over the Arabian Sea

Abstract

Some aspects of interactions that take place between the water surface of the Arabian Sea and the summer monsoon circulation are investigated. Over large portions of the Arabian Sea (and also the Bay of Bengal) there is a rapid warming of the surface water during late winter and early spring. The maximum temperatures are observed around May, at the time of the establishment of the southwest on, monsoon circulation. There is then cooling of the waters to a minimum observed in August-September, followed by a secondary maximum October-November. This trend differs from what is commonly observed over most of the tropical oceans, where there is a single water temperature maximum in late summer and a minimum in late winter. The water cooling in early summer appears to be a direct result of the establishment of the southwest monsoon regime. The resulting inter-relationships have pronounced effects on the properties of both the water body and the monsoon circulation.

In order to assess the role to heat flux in the water-cooling, computations of components of the energy balance were carried out for various stations in the Arabian Sea and vicinity. Rather large rates of heat flux by evaporation were obtained the west central portions of the Arabian Sea. It is shown that the evaporation makes a major contribution to the water-cooling in that area.

Effects of the air-sea interactions on the atmospheric current investigated by analysis of aeteorological  sounding along the monsoon surface trajectory. A characteristic low-level inversion in the levels from 900 to 700mb is found over most of the oceanic area. The moisture is concentrated below the inversion. Above the inversion the air is dry and unstable. Some of the implications of the presence of this thermal and moisture distribution on monsoon weather are discussed briefly.