Regional simulation of aerosol impacts on precipitation during the East Asian summer monsoon

Ensemble simulations with the WRF-Chem model are performed to examine aerosol impacts on precipitation over China during the East Asian summer monsoon (EASM). In the first EASM phase (May 6 - June 13), monsoonal rain band is located to the south of high aerosol areas. The surface cooling by the aerosol radiative effect induces an anti-cyclonic circulation in northern China, causing a precipitation decrease over southern China. The aerosol microphysical effect tends to broaden the precipitation region. In the second EASM phase (June 14 -August 5), the precipitation band jumps to northern China, where heavy pollution locates. By serving as CCN, the aerosol microphysical effect causes a reduction of local cloudiness and induces ascent to the north and descent to the south, leading to a precipitation shift from south to north. The aerosol radiative effect strengthens such a meridional asymmetry. Moisture budget analysis shows the aerosol-induced anomalies of precipitation in both phases are mainly contributed by the changes in vertical velocity associated with convection, while the horizontal advection of moisture plays a non-negligible role. Our study highlights that aerosol effects on EASM precipitation depend on the location of monsoon precipitation band and its relative location to aerosols, which may be a main factor contributed to the discrepancy in literature regarding to aerosol impacts on the so-called “southern flood and northern flood” over China.