On the relationship between Indian ocean sea surface temperature and Asian summer monsoon

Indian Ocean SST has been thought to play a weaker role in Indian summer monsoon rainfall than does the equatorial eastern Pacific SST. In this study we show that on the tropical biennial oscillation (TBO, 2-3 year) time scale the Indian monsoon rainfall has significant positive correlations with the Indian Ocean SST and moisture flux transport in the preceding winter and spring. The effect of this SST influence is quite different from the remote forcing of the Indian monsoon rainfall by the eastern Pacific SST, which is more dominant on the El Nino-Southern Oscillation (ENSO, 3-7 year) time scale. We conclude that while the eastern Pacific SST and the Eurasian land temperature both may affect the monsoon on the ENSO time scale, they are not important on the TBO time scale. Our results support the tropical and local feedback theories of TBO that this most important component of the monsoon variation is largely influenced by the Indian Ocean SST and interactions within the tropical atmosphere-ocean system (Chang and Li, Nichols).