Impact of eastern equatorial Indian ocean during positive tropical dipole on regions over Tamilnadu and coastal Andhra Pradesh

Abstract

The main objective of the present work is to investigate the influence of eastern Sea surface temperature (SST) anomalies during the Positive Tropical Indian Ocean dipole (PTIOD) events on regional summer monsoon rainfall especially over Tamilnadu and Coastal Andhra Pradesh (A. P.) for the period of 1980-2009. There were 7 strong PTIOD events recorded during the period of study which are accompanied by significant increase in the seasonal summer monsoon rainfall over India. Averaged SST anomalies (SSTA) over the EQ.ESIO (Equatorial Eastern South Indian Ocean) during AMJ (April, May, June) shows that colder (warmer) EQ.ESIO during AMJ and positive TIOD events were associated with the decreasing (increasing) tendency of summer monsoon rainfall over Tamilnadu and coastal A.P. The statistical analysis shows the correlation coefficient of 0.59 and 0.79 between AMJSST anomalies and the rainfall over Tamilnadu and Coastal A. P. respectively. Wind anomalies during PTIOD years with negative AMJSSTA, transports the cold upwelled oceanic current off Sumatra-Java towards the South West Bay of Bengal (SWBOB) and caused anomalous SST cooling in the region. Thus, the low level southerly wind reaching over the SWBOB during AMJ enforced the colder oceanic surface temperature of the region during the month of maximum solar insolation and thereby weak thermal gradient was observed with the shifting of the convective activity towards the south-east/northern Bay of Bengal (BOB). Moreover, less moisture advection with less convective activity in SWBOB region during pre-monsoon season may be the caused of the below-normal rainfall over Tamilnadu and coastal A. P. sub-divisions during June, July, August and September (JJAS)