Detection of Bay of Bengaleddies from Topex and in situ observations

Author(s): Gopalan AKS, GopalaKrishna VV, Ali MM, Sharma R

Abstract

Oceanic eddies have warm or cold temperatures and high or low sea surface height (SSH) at the center depending upon the direction of rotation. However,since the Bay of Bengal waters are highly stratiŽ ed, sea surface temperature (SST) gradientsmay not be detectable even though the subsurface temperature sections and the SSH show prominent eddy signatures. In this investigation, SSH observationsfrom TOPEX altimeter data and the expendable bathy thermograph (XBT) temperature sections along the Madras–Andamans track have been analyzed to study the Bay of Bengal eddies. Several cyclonic and anticyclonic eddies are identiŽ ed from the TOPEX altimeter observations. These eddieslocated along the ship’s tracks have signiŽ cant variationsin amplitudes and show good qualitative agreement with the subsurface isotherm features (troughs and ridges) of the in situ temperature proŽ les. However, this agreement does not extend to the surface and hence SST patterns are not good indicators of eddy positionsin the Bay of Bengal where the waters are highly stratiŽ ed. Therefore, a better approach to the study of eddies in regions like the Bay of Bengal is to use SSH observations. Due to the extensive spatial coverage of remote sensing observations, the exact position and shape of the eddies can be characterizedfrom altimeter-derivedSSH observationswhich is not possible using the limited in situ proŽles. Interannual variations in both the positions and intensities of eddies are observed during the study period.

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