During the Southwest Monsoon strong upwelling and distinctive oceanic eddy structures form adjacent to and off of the coast of Somalia and further north in the Arabian Sea. Research vessel cruises have identified very cold water (<20°C) in filaments and fronts in this area, but our knowledge of their space-time structure and evolution is incomplete. These structures appear in high-resolution ocean general circulation model simulations, but are not present in the global SST analyses.

Using the TRMM microwave SST data we here provide a view of these structures and their evolution, in weekly SST. The satellite data indicate that both the climatological seasonal cycle and its interannual variability are larger than indicated from COADS or the NCEP SST product. Based on the TRMM microwave SST, accurate monthly mean SST over the western Indian Ocean can be obtained only if the cold feature data are properly sampled. The subseasonal, seasonal and interannual SST variability in this region are dominated by changes in the upwelling plumes. Thus, variability of the ocean processes that control the spin up and evolution of the ‘Great Whirl’ and other western Indian Ocean eddy structures may thus determine interannual SST variability in the region. Our present understanding of the low frequency variance of SST in the region, and the covariability of SST with other climatic parameters, over the Indian basin need to be revisited in light of these results.