January 1999 Indian ocean cooling event

Unexpectedly strong sub-seasonal SST variability over the tropical Indian Ocean has been observed by the TRMM microwave imager, which provides unprecedented tropical SST information in the presence of clouds. In January-February 1999 SST averaged over an area 20° longitude by 10° latitude cooled by ∼1.5°C over 10 days and warmed by ∼1.25°C in the following week. Local changes were up to ±3°C. There were strong variations in atmospheric convection and surface wind stress associated with the SST variability. The evolution of the convection suggests a feedback from the SST changes into atmospheric convection. Net air-sea heat-flux cannot account for the observed cooling; oceanic processes are fundamental to this event. The roles of such sub-seasonal ocean-atmosphere interactions in the evolution of the Madden-Julian Oscillation, the seasonal and the interannual variability of Indian Ocean SST deserve further investigation.