Anomalous warming of the western equatorial Indian Ocean in 2007: Role of ocean dynamics

Abstract

In this study, observational data, together with the simulations from a high-resolution numerical ocean model, are used to identify the processes responsible for the anomalous warm sea surface temperature (SST) in the equatorial Indian Ocean during late spring/early summer in 2007. Our analysis suggests that the SST in the western equatorial Indian Ocean (WEIO) remained unusually warm owing to the combined influence of the wind induced and reflected Rossby waves in the equatorial Indian Ocean. Anomalous westerly wind burst in the equatorial Indian Ocean in early April generated an eastward propagating downwelling Kelvin wave, which got reflected from the eastern boundary as a downwelling Rossby wave and propagated to the WEIO. The easterlies appeared during the second fortnight of April generated another downwelling Rossby wave, which also propagated to the WEIO. Thus a couple of downwelling Rossby waves, reflected and direct wind induced, propagated to the WEIO, deepened the thermocline and prohibited cooling in the WEIO during the early months of summer monsoon season. This study demonstrates the importance of the equatorial winds and associated oceanic dynamics in modulating the SST variability in the WEIO.