Distinct effects of Fine and Coarse Aerosols on Microphysical Processes of Shallow Precipitation Systems in Summer over Southern China

The densely populated South China, adjacent to the South China Sea, which is associated with shallow precipitation during summer, makes it a natural experimental region for studying the impact of aerosols on shallow precipitation events. Using 8 years of GPM DPR, MERRA-2 aerosol, and ERA reanalysis data, this study investigates the potential influence of coarse and fine aerosol modes on the precipitation structure and microphysical processes of shallow precipitation in South China. Statistical results indicate that during coarse aerosol-polluted conditions, shallow precipitation clouds have a lower median Storm Top Height (STH, ~3.2 km), but a higher mean near-surface rainfall (RR, ~1.78 mm h-1), characterized by high concentrations of large raindrops, mainly driven by significant collision-coalescence processes (accounting for 74.1 %). Conversely, during fine aerosol-polluted conditions, shallow precipitation clouds develop deeper median STH ~3.7 km with lower surface RR characterized by a low concentration of small hydrometeors, resulting from increased breakup processes (33.1 %) and reduced collision-coalescence processes (69.6 %). The coarse (fine) aerosols act as promoters (inhibitors) of the radar and radar reflectivity in the profile of shallow precipitation, regardless of dynamic and humid conditions. The effect of coarse aerosols in promoting precipitation and the inhibiting effect of fine aerosols are the most significant under low humidity conditions, mainly attributed to the significantly enhanced collision-coalescence processes, exceeding 22.2 %. Furthermore, the increase in RR above 3 km during coarse aerosol-polluted environments is mainly driven by the high concentration of hydrometeors in low instability conditions, while by large hydrometeors in high instability environments.