Variability of the flow field in the inner shelf along the central east coast of India during April, 1989

Abstract

Current measurements collected along the inner shelf off the central east coast of India (water depth ⋍ 50 m) at three stations, A (17°59′N, 83°53.9′E), B (17°00′N, 82°32.1′E) and C (16°31.3′N, 82°21.8′E) during the cruise 211 of R.V. Gaveshani (April 1989) are discussed. Data analysis show there to be two layer circulation at Sta. A: a northerly flowing current, which is restricted to the surface and a southerly flowing current at mid water depth and near the bottom. Southerly flowing current occupies the whole of the water column at Sta. B and northerly flowing current at Sta. C. The striking divergence of the mean velocity field between Stas B and C is due to disparate advection states of the local eddy field. The mean southerly velocity of 6–12 cm s −1 from the surface to 45 m depth at Sta. B, and northerly velocity of 84–121 cm s −1 from the surface to 45 m at Sta. C suggesting that the meridional flow is substantially baroclinic. The onshore-offshore component of the currents is much smaller than the alongshore current at all the stations. The upwelling circulation off Kakinada was generally three layered: the surface offshore flow was confined to approximately the upper 10 m, the compensating onshore flow was maximum at mid depth (about 30 m) and there was weak offshore flow along the bottom. The large values of both K e and K m encountered at Sta. C are consistent with the idea that, in this region, baroclinic instability is converting potential energy of the strong mean flow into fluctuation energy. The overall K e decreases northward from Sta. C to Sta. A represent the interior of the northern anticlockwise gyre.