January 1999 Indian Ocean cooling event

Unexpectedly strong sub-seasonal SST variability over the tropical Indian O cean has been observed by the TRMM microwave imager, which provides unprece dented tropical SST information in the presence of clouds. In January-Febru ary 1999 SST averaged over an area 20 degrees longitude by 10 degrees latit ude cooled by similar to1.5 degreesC over 10 days and warmed by similar to1 .25 degreesC in the following week. Local changes were up to +/-3 degreesC. There were strong variations in atmospheric convection and surface wind st ress associated with the SST variability. The evolution of the convection s uggests a feedback from the SST changes into atmospheric convection. Net ai r-sea heat-flux cannot account for the observed cooling; oceanic processes are fundamental to this event. The roles of such sub-seasonal ocean-atmosph ere interactions in the evolution of the Madden-Julian Oscillation, the sea sonal and the interannual variability of Indian Ocean SST deserve further i nvestigation.