A summary of results on thermohaline variability in the upper layers of the east central Arabian Sea and Bay of Bengal during summer monsoon experiments

Some important features of thermohaline variability emerged from several case studies carried out utilising short time series measurements of surface marine meteorological parameters, vertical profiles of temperature and salinity, and currents. These were measured at discrete depths at selected stations in the east central Arabian Sea, the Bay of Bengal and the equatorial Indian Ocean from USSR and Indian Ships during the field experiments of ISMEX-73, MONSOON-77 and MONEX-79. The observed changes in the variable surface meteorological forcing, response characteristics of the mixed layer and thermohaloclines in the east central Arabian Sea under the onset and progress of the summer monsoon are documented and described. The efficacy of a simple one-dimensional numerical model in simulating the mixed layer cooling and deepening is evaluated. In the Bay of Bengal the evidence for a suggestive relationship between an accumulation of heat in the upper layers and the genesis of monsoon depression/cyclonic storms is presented. The role of a severe cyclonic storm in producing dramatic transient variations in the upper layer characteristics is highlighted. The observed eastward depression in the thermocline along the equator is described.