The role of cloud glaciation in modulating aerosol susceptibility: insights from cold-air outbreak stratiform clouds over the Northwest Pacific

Abstract Cloud susceptibility to aerosol (CSA) refers to their sensitivity to increases in condensation nuclei (CN) concentration. Yet, CSA in mixed-phase clouds remains largely unexplored. This study investigates CSA in marine boundary layer clouds during cold-air outbreaks, where ice particles are often present, using the WRF model coupled with the NTU microphysical scheme. In warm clouds, the CSA of cloud albedo (precipitation) remains positive (negative); however, this sensitivity weakens as CN concentration increases. In mixed-phase clouds, CSA signal remains positive in sign but becomes weaker (relative to the warm clouds) and non-monotonic. Reflecting the interplay of multiple microphysical processes under varying aerosol conditions, cold precipitation increases with increasing aerosol loadings and peaks at intermediate CN concentrations, shaping the CSA of cloud albedo into an inversed-N pattern. Aside from microphysical responses, cloud fraction—a macro-physical feature—also shows susceptibility to aerosol effects. As CN increases, cloud fraction tends to decrease, which can mitigate up to one-third of the cloud albedo CSA in warm clouds and three-fourths in mixed-phase clouds.