Response of the upper layers of the northern and central Bay of Bengal to the atmospheric events during summer monsoon of 1999

oN, 87 o E (TS1) and 17.5 o N, 89 o E (TS2). Two stations, separated by 545 km, were selected based on the fact that the occurrence of organized convection was high at both locations. From oceanographic point of view, TS1 and TS2 were located within anti-cyclonic and cyclonic gyres respectively, that shifted westward at a rate of 6.3 cm/sec. During the BOBMEX-99 observational period, three systems were formed over the northern BoB. Because of the proximity of TS2 to various systems, its influence was more reflected on the atmospheric and oceanic parameters at this location than at TS1. During the initial stages, atmospheric pressure at TS2 dropped by 3-6 mb and the atmosphere and the ocean surface cooled by 1.5 to 3 o C and 0.35 to 0.85 o C respectively. Associated with the systems, thermal inversions of 0.1 o C to 0.15 o C were observed at the base of isothermal layer. Surface salinity dropped by 0.8 psu and 1.2 psu with the rainfall during 31 July-1 August (70 mm) and 15-6 August (>90 mm) respectively. The freshwater influx resulted in the formation of a barrier layer at TS2, which showed a positive relation thermal inversions. During BOBMEX99 period, the systems were formed whenever there was large positive salinity gradient; sea surface temperature exceeded 28.5 o C and heat content with respect to 28.3 o C exceeded ~3×10 7 Jm -2 .