Aerosol-drizzle-cloud interaction in marine boundary layers: Impacts of large-scale conditions

Recent field observations and modeling studies suggested that the aerosol-cloud-drizzle interaction may be responsible for the observed cloud reduction and the transformation from the closed-cell to open-cell structure. Evaporation of rain drops is proposed in the studies to be an essential mechanism that drives the transformation as it changes the local thermal stability and promotes vertical motion. This study focuses on the issue of the impact of large-scale conditions including sea surface temperature, subsidence, and the strength of the inversion. It is motivated by the facts that not all precipitating stratus closed-cell clouds are transformed to open-cell cumulus type clouds. What are the fundamental large-scale meteorological parameters that can regulate the aerosol-drizzle-cloud interaction?

We apply COAMPS-LES to the drizzling cloud cases observed in VOCALS-Regional Experiment. The model uses a two-moment scheme for the cloud and rain processes, and a simple vertical velocity dependent cloud droplet activation scheme. The LES domain covers 50 km „e 50km „e 3 km domain with the horizontal resolution being 250 m and the vertical 50 m. The model simulation is successful in producing the closed-cell to open cell cloud transformation under the observed large-scale conditions. We then conduct a series of experiments with the different large-scale conditions. Currently, we are analyzing our results; we will report the results in details in the presentation.