Southern Indian Ocean SST variability and its relationship with Indian summer monsoon

Abstract

Sea surface temperature (SST) variability in the Southern Indian Ocean (SIO) region and its relationship to Indian summer monsoon rainfall is investigated. A correlation analysis is used to examine the relation between SIO SST variability and Indian monsoons with lag‐lead times of up to two years (eight seasons). A significant positive correlation is found between tropical SIO SST and the All India Rainfall Index (AIRI) in the March‐May and December‐February seasons before the onset of monsoon. The SST in the region south of 35°S is positively correlated with AIRI six, seven, and eight seasons before the onset of monsoon. A maximum correlation of 0.47 is found for the region south of 35°S, with a confidence level of 99%. Based on this correlation, we have defined SST indices for the central SIO (CSIO), the northwest of Australia (NWA), the SIO, and the Antarctic Circumpolar Current (ACC). These indices seem to be early predictors of Indian monsoons when their relationship with AIRI is examined. The predictive skill of these indices is also tested by multivariate linear regression. The consistency of this relationship is verified by the removal of the El Niño Southern Oscillation (ENSO) signal from SST data and is found to be unaffected by the ENSO signal, except in the region west of Australia.