Role of aerosols in modulating the convection over the South China Sea associated with boundary layer clouds during boreal winter

During the winter monsoon, a high-pressure ridge extends from Siberia to the northern South China Sea (SCS). This system brings northeasterly cold air, which rises over the warm sea surface of the SCS, causing atmospheric instability and frequent convection over the region. This continental cold-air outbreak also forms cloud streets over the northwestern Pacific. In this study, we investigated the effects of aerosol-cloud interactions over the upstream northwestern Pacific (e.g., the East China Sea) on convective activity in the downstream tropical area (e.g., the South China Sea). To achieve this, we selected two distinct cases associated with boundary layer clouds and conducted sensitivity experiments using different aerosol types—such as anthropogenic or continental, oceanic, and mixed aerosols—to simulate convection characteristics over the SCS. For our analysis, we employed the aerosol-sensitive National Taiwan University (NTU) multimoment microphysical scheme coupled with the Weather Research and Forecasting (WRF) model. Our results indicate that the thermal and moisture properties of the winter cold-air mass reaching the SCS and tropical oceans can be significantly influenced by anthropogenic aerosols produced over the East Asian continent. We also examined variations in orographic rainfall patterns over different regions, such as northeastern Taiwan and coastal Vietnam, in relation to these boundary layer clouds and their sensitivity to the choice of aerosol types. This study highlights the importance of using a multimoment microphysical scheme capable of accounting for diverse aerosol types to improve simulation accuracy with the WRF model.

Keywords: Aerosol-cloud interaction, South China Sea, Boundary layer clouds, WRF