DIAGNOSIS OF UPWELLING AND DOWNWELLING SIGNALS IN THE BAY OF BENGAL

The monthly and interannual variations of upwelling and downwelling signal in the Bay of Bengal (BOB) have been investigated in this study using 52-years Simple Ocean Data Assimilation products (SODA). The intensity of upwelling and downwelling in the southern part is much higher than the other parts of BOB. The upwelling and downwelling in the BOB is not only driven by wind stress curl but also has significant contribution from the remote effect. The eastern coast and the central BOB are mostly dominated by remote effect. The wind-stress curl driven upwelling and downwelling in the open ocean is almost balanced by remote effect and as a result the central BOB does not show any upwelling and downwelling features during summer season. The increase of wind stress curl in the recent years over this region is another important outcome of this study.The Wind Stress Curl (WSC), vertical velocity and remote effect are influenced by the tropical climatic events like El-Niño/Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD). The upwelling and downwelling signals became stronger during El-Niño and La-Niña years but during the concurrent ENSO and IOD years (1988 and 1997) this signals show different behavior for different boxes. There are quite similar responses of the BOB with El- Niño and positive IOD events and also with La- Niña and negative IOD events.