Impact of middle east dust on subseasonal-to-seasonal variability of the Asian summer monsoon

摘要

We investigated the effect of increased spring (April-May) dust aerosol over the Arabian Peninsula (AP) on the subseasonal-to-seasonal (S2S) variability of the Asian summer monsoon (ASM) using MERRA-2 re-analysis data (1980-2018). Result shows that abundant AP spring dust leads to more dust covering the AP and Pakistan northwestern India (PNWI) during May-June, causing a cooler land surface and a warmer lower and middle atmosphere with enhanced local atmospheric stability. However, the warmer atmosphere increases the meridional temperature gradient, boosting moisture transport from the Arabian Sea to PNWI, causing increased convective potential energy in PNWI region. As season advances, the accumulated convection potential energy eventually breaks through the local stability, via the elevated heat pump (EHP) effect, increasing precipitation over PNWI. In July and August, cloud radiation-circulation feedback further enhances the warming of the upper troposphere, strengthening precipitation in PNWI. Dynamical adjustments of large-scale circulations induced by the feedback strongly modulate ASM precipitation. Over southern and central China, precipitation is reduced, in conjunction with a contraction of South Asian High, and the development of an anomalous east-to-west oriented upper-level wavetrain in July. In August, the upper level wavetrain undergoes strong wave-mean flow interaction, culminating in the development of an anticyclonic center with drought conditions over northeast China, Korea and Japan. Over the Indian subcontinent, increased precipitation in PNWI plays an important role in initiating the EHP feedback leading to increased precipitation over the Indian subcontinent, and in modulating the jetstream-wave interaction in downstream East Asian regions in July-August.