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

Oceanic eddies have warm or cold temperatures and high or low sea surface h eight (SSH) at the center depending upon the direction of rotation. However , since the Bay of Bengal waters are highly stratified, sea surface tempera ture (SST) gradients may not be detectable even though the subsurface tempe rature sections and the SSH show prominent eddy signatures. In this investi gation, SSH observations from TOPEX altimeter data and the expendable bathy thermograph (XBT) temperature sections along the Madras-Andamans track hav e been analyzed to study the Bay of Bengal eddies. Several cyclonic and ant icyclonic eddies are identified from the TOPEX altimeter observations. Thes e eddies located along the ship's tracks have significant variations in amp litudes and show good qualitative agreement with the subsurface isotherm fe atures (troughs and ridges) of the in situ temperature profiles. However, t his 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 ar e 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 exte nsive spatial coverage of remote sensing observations, the exact position a nd shape of the eddies can be characterized from altimeter-derived SSH obse rvations which is not possible using the limited in situ profiles. Interann ual variations in both the positions and intensities of eddies are observed during the study period.