An investigation of the influence of the southern annular mode on Indian summer monsoon rainfall

The present research was aimed at identifying the influence of the southern annular mode on the Indian summer monsoon (ISM) by investigating the inter-annual as well as seasonal variation in the southern annular mode index (SAMI) and the ISM rainfall. It is shown that each month of the ISM is influenced by the southern annular mode of different months. The association between the June SAMI and July rainfall was found to be significant as well as important. The investigation was carried out with the NCEP/NCAR reanalysis dataset. The result shows that the monsoon rainfall anomaly is significantly and negatively correlated with the SAMI. The influence of the June SAMI is estimated with sea surface temperature (SST), horizontal wind at 850 hPa pressure level, vertical wind and moisture convergence. The result shows the existence of warm sea surface at 30 degrees S during high SAMI years which is surmised to control the cross-equatorial flow during the ISM. It was also observed that the enhanced southerly flow over the south of India is divided into two parts. The major flow is observed towards the western Arabian Sea, subsequently turning clockwise and moving towards the western part of India through the north Arabian Sea. The result further shows that an intense ascending motion from the equator to 30 degrees N along the western coast coincides with the low rainfall region. These conditions may lead to an enhanced divergence zone over the western and northeastern region of India which, in turn, may result in less rainfall over India.