Redistribution of Indian summer monsoon by dust aerosol forcing

Abstract

Previous studies based on models and observations show that dust aerosols have an impact on the timing and distribution of the Indian summer monsoon but the transition of various Indian summer monsoon-associated atmospheric features which unfolds in the process is still not clear. Through regional climate simulations, this study identifies the different phases of the change in the mean distribution of monsoon related characteristics in response to local dust forcing. The deposition of dust along the slopes of the Tibetan Plateau results in a heated atmospheric column (elevated heat pump) over there starting from May. This drags the monsoonal flow towards the foothills of the Himalayas before the conventional monsoon onset over India, which tends to decrease the rainfall over central India and increase it along the foothills of the Himalayas during May and June. July is the period of transition during which the reversal of various atmospheric conditions takes place. The elevated heat pump completely vanishes with the wet deposition of dust, which reduces the vertical wind over the Tibetan Plateau. The removal of dust increases the temperature over the Indo-Gangetic plain, which efficiently drags the moisture carrying southwesterly towards central India. Meanwhile, stronger horizontal divergence of moisture towards the Bay of Bengal reduces the rainfall over central India and these atmospheric conditions further intensify during August. These results provide strong evidence of the role of dust aerosols in shaping the Indian summer monsoon distribution over India.