The Impact of the Tropical Indian Ocean on South Asian High in Boreal Summer

The tropical Indian Ocean (TIO) is warmer than normal during the summer whenor after the El Ni~{n}o decays. The present study investigates the impact of TIO SSTon the South Asian High (SAH) in summer. When the TIO is warmer, the SAH strengthensand its center shifts southward. It is found that the variations in the SAH cannot beaccounted for by the precipitation anomaly. A possible mechanism is proposed to explainthe connection between the TIO and SAH: warmer SST in the TIO changes the equivalentpotential temperature (EPT) in the atmospheric boundary layer (ABL), alters the temperatureprofile of the moist atmosphere, warms the troposphere, which produces significant positiveheight anomaly over South Asia and modifies the SAH.An atmospheric general circulation model, ECHAM5, which has a reasonable prediction skillin the TIO and South Asia, was selected to test the effects of TIO SST on the SAH. Theexperiment with idealized heating over the TIO reproduced the response of the SAH to TIOwarming. The results suggest that the TIO-induced EPT change in the ABL can account forthe variations in the SAH.