Satellite observations of intense intraseasonal cooling events in the tropical south Indian Ocean

Abstract

Intense intraseasonal cooling events in the tropical south Indian Ocean are examined using eight years of TRMM observations. These events occur almost every year during austral summer when the intertropical convergence zone is displaced south of the equator and roughly collocated with a thermocline ridge. Composite maps of SST, OLR and surface winds, based on eleven cooling events with SST exceeding 1°C, suggest that reduced solar radiation, enhanced evaporation and possibly strong entrainment over the thermocline ridge all play a role in the SST cooling. OLR and covariability in SST exhibit latitudinal variations in spectrum. A distinct southern mode around 10°S-5°S exhibits a peak in coherence-squared at a period of 65 days. In contrast, an equatorially symmetric mode has a coherence-squared peak at 35 days. This may hint at a possible feedback onto the atmosphere from strong intraseasonal SST variability over the south Indian Ocean. Copyright 2006 by the American Geophysical Union.