Large subseasonal SST variability in the tropical Indian Ocean

The TRMM imaging microwave SST data set indicates that there is unexpectedly strong SST variability on subseasonal time scales over the tropical Indian ocean. Warm and cold anomalies of weekly SST in excess of 1.5C are found over large regions of the basin. Strong variations in tropical convection, as indicated by changes in outgoing long wave radiation, are associated with the SST anomalies. There are also substantial local wind stress and wind stress curl anomalies before and during the SST anomalies. Simple scaling and heat-flux estimates suggests that the SST anomalies are unlikely to have been forced primarily by changes in the net air-sea heat flux. Only access to cold subsurface water (through mixing and advection) can produce cooling of the observed rates, and horizontal advection can rapidly warm. There appears to be significant ocean-atmosphere interaction in the tropical Indian Ocean on sub-seasonal time scales, which deserves further investigation as a mechanism for understanding and forecasting monsoon breaks.

`special session on Air-sea Interaction Studies Using Satellite Observations.'