OBSERVATIONS OF THE WESTERN BOUNDARY CURRENT OF THE BAY OF BENGAL FROM A HYDROGRAPHIC SURVEY DURING MARCH 1993

The characteristics of the Western Boundary Current of the Bay of Beng al (BBWBC) are studied utilising MICOM STD profiles collected during 9 -23 March 1993 aboard F.O.R.V. Sagar Sampada from an area between 11 d egrees N and 18 degrees N and from the coastline to similar to 400 km offshore. North of 15 degrees N, the waters nearer the coast were warm er and more saline, with a cross-shore gradient associated with an alo ngshore current regime. A cold, low-salinity tongue was found offshore north of 15 degrees N. The isotherms in the vertical sections from 11 degrees N to 18 degrees N showed an offshore deepening, indicating a northerly flow. The nearshore isotherms and isohalines along the 13 de grees and 14 degrees N sections, however, indicated the presence of a cyclonic eddy. The geostrophic flow regime was dominated by the presen ce of eddies and poleward hows. The poleward flow, with a cross-stream of dimension 30 km, was stronger (>90 cm/s), and extended deeper (500 m) in the northwestern Bay. This flow was regarded as the BBWBC durin g March 1993. South of 13 degrees N, the poleward flow appeared as par t of an anticylconic eddy with speeds up to about 40 cm/s. The net vol ume transports were directed northward across all the sections (except the 13 degrees N section) with magnitudes varying between 3 and 17 Sv (1 Sv = 10(6) m(3)/s). Southward transport of 3 Sv was observed nearer the coast along 14 degrees N due to the cyclonic eddy. The hydrograph ic features along a section from off Madras to Andamans during May 198 7 exhibited the characteristics of a well-developed WBC of a subtropic al gyre. The volume transport in the BBWBC region was found to be cons iderably higher in May 1987 (16 Sv) than in March 1993 (5 Sv). It is c oncluded that the flow regime inferred in the western Bay during March 1993 represented the developing phase of the western boundary current system, which appeared first at the northwestern Bay. (C) 1997 Elsevi er Science Ltd.