Observation of the western boundary current of the Bay of Bengal Deep-Sea Res 44:135-145

Author(s): Sanilkumar KV, Kuruvilla TV, Jogendranath D, and Rao RR

Abstract

The characteristics of the Western Boundary Current of the Bay of Bengal (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°N and 18°N and from the coastline to ∼400 km offshore. North of 15°N, the waters nearer the coast were warmer and more saline, with a cross-shore gradient associated with an alongshore current regime. A cold, low-salinity tongue was found offshore north of 15°N. The isotherms in the vertical sections from 11°N to 18°N showed an offshore deepening, indicating a northerly flow. The nearshore isotherms and isohalines along the 13° and 14°N sections, however, indicated the presence of a cyclonic eddy.

The geostrophic flow regime was dominated by the presence of eddies and poleward flows. 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 during March 1993. South of 13°N, the poleward flow appeared as part of an anticylconic eddy with speeds up to about 40 cm/s. The net volume transports were directed northward across all the sections (except the 13°N section) with magnitudes varying between 3 and 17 Sv (1 Sv =106 m3/s). Southward transport of 3 Sv was observed nearer the coast along 14°N due to the cyclonic eddy.

The hydrographic features along a section from off Madras to Andamans during May 1987 exhibited the characteristics of a well-developed WBC of a subtropical gyre. The volume transport in the BBWBC region was found to be considerably higher in May 1987 (16 Sv) than in March 1993 (5 Sv).

It is concluded 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.

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