The Western Boundary Current of the seasonal subtropical gyre in Bay of Bengal

Author(s): Shetye SR, AD Gouveia, SSC Shenoi, DSundar, GSMichael, et al.

Abstract

Hydrographic data collected during March-April 1991 show the presence of a poleward current along the western boundary of the Bay of Bengal of about 10 degrees N carrying warmer waters of southern origin. The inshore side of the current was markEd. by cooler, more saline waters brought to the surface due to the presence of the current which transported approximately 10 x 10 sup(6)m sup(3)/s. The hydrography is suggestive of many of the features that have been associated with the western boundary currents of the subtropical gyres of the world oceans:a recirculation zone, waves, eddies, etc. These features, however, were not satisfactorily resolved in the data. Using available climatologies of monthly mean ship drifts, seasonal hydrography, and monthly mean wind stress, we propose that the poleward current is the western boundary current of a seasonal anticyclonic subtropical gyre which forms in the Bay during January, is best developed during March-April, and decays by June. The gyre and the western boundary current are unique because of their seasonal character. The pattern of circulation leading to formation and decay of the gyre is reproduced reasonably well in the computation of the monthly mean barotropic transport inducEd. by the curl of wind stress, which has a well-defined annual cycle due to the monsoon and which is conductive to the formation of an anticyclonic gyre only during the months of January-May. The pattern of circulation due to barochlinic transport inducEd. by the wind stress, however, is not known at present, and this makes it difficult to conclude unequivocally that e wind stress curl over the bay is the sole mechanism to force the gyre.

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