Detection of Bay of Bengal eddies from TOPEX and in situ observations

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 stratified, sea surface temperature (SST) gradients may not be detectable even though the subsurface temperature sections and the SSH show prominent eddy signatures. In this investigation, SSH observations from 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 identified from the TOPEX altimeter observations. These eddies located along the ship's tracks have significant variations in amplitudes and show good qualitative agreement with the subsurface isotherm features (troughs and ridges) of the in situ temperature profiles. However, this agreement does not extend to the surface and hence SST patterns are not good indicators of eddy positions in the Bay of Bengal where the waters are highly stratified. 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 characterized from altimeter-derived SSH observations which is not possible using the limited in situ profiles. Interannual variations in both the position and intensities of eddies are observed during the study period