Effects of local and remote aerosols on the cloud and precipitation of an extreme-rain-producing MCS

Mesoscale convective systems (MCSs) are important producers of severe weather events and are influenced by aerosols that are either locally emitted or remotely transported. Despite widespread recognition of aerosol–MCS interactions, how aerosols from local and distinct sources alter MCS cloud microphysics and precipitation remains inadequately quantified. To address this knowledge gap, this study investigates an extreme-precipitation-producing MCS event in South China affected by concurrent local anthropogenic pollution and remote biomass-burning aerosols. Using the Weather Research and Forecasting-Chem model, four sensitivity experiments are conducted, including clean, local emissions only, remote transport only, and all emissions scenarios. For the investigated MCS, results show that aerosol perturbations increase the convective-region-mean rainfall intensity by around 20%. Local aerosols, characterized by high hygroscopicity and high concentrations in the lower troposphere, promote droplet activation and exert a relatively stronger influence on precipitation during the early analysis period, but are rapidly depleted by wet scavenging. In contrast, remotely transported aerosols are less susceptible to wet scavenging and maintain a more persistent aerosol supply throughout the MCS lifecycle, resulting in a relatively stronger influence during the late analysis period in this event. Moreover, the presence of remote aerosols in the remote-only and full emission experiments may contribute to a larger stratiform fraction by generating smaller snow particles in the stratiform region with slower fall speeds. Our results underscore the necessity for an accurate representation of the sources, vertical distribution, and hygroscopicity of aerosols in numerical weather prediction models.