The role of air-sea interactions in regulating the thermal effect of the Tibetan-Iranian Plateau on the Asian summer monsoon

The thermal effect of the Tibetan-Iranian Plateau (TIP) on the Asian summer monsoon and the role of air-sea interactions over the Indian Ocean in regulating the effects of the TIP are explored. The results demonstrate that the direct thermal effect of the TIP produces a lower troposphere cyclonic circulation in the area surrounding the TIP and increases the continental precipitation over South and East Asia. It also decreases the precipitation over the tropical Indian Ocean and increases the sea-surface temperature (SST) of the tropical Indian Ocean with a large gradient zone located along 10 degrees N but decreases SST of the western coast of Indonesia. In the lower troposphere, the air-sea interaction induced by the TIP thermal forcing produces an anticyclonic circulation surrounding the TIP and a stronger westerly flow to the south of the anticyclone. A circulation dipole thus forms to the south of the TIP. Together with this horizontal dipole, a meridional circulation dipole is generated to the south of the TIP, which is characterized by strong air ascent from 10 to 15 degrees N where a strong westerly flow occurs, and the descent of air over the southern slope of the TIP and south Hemisphere. These results demonstrate that the indirect effect of the air-sea interaction over the Indian Ocean induced by the TIP thermal forcing is to counteract its direct effect on the Asian summer monsoon. The uncertainty of this indirect effect is also discussed.