Simulation of marine stratocumulus using the super-droplet method: Numerical convergence and comparison to a double-moment bulk scheme using SCALE-SDM 5.2.6-2.3.0

Abstract. Marine stratocumulus clouds play an important role in the planet’s radiation budget by reflecting the incident solar radiation. Some studies have shown that the uncertainty in temperature projections in global warming simulations is mainly caused by the representation of marine low clouds in global climate models. Using the Super Droplet Method (SDM), an advanced and highly accurate particle-based numerical simulation method for cloud microphysics, the characteristics and morphology of the simulated clouds are closer to those of natural clouds. We explore separately how small a grid length is necessary for accurate simulations of stratocumulus using the SDM and a double-moment scheme called SN14 which is a traditional and simpler cloud microphysics scheme and how many Super-droplet number per grid is required for an accurate simulation using SDM. This result can be used as a reference for future related research, saving computational resources while ensuring the accuracy of the simulation. The results of both schemes are compared with the results of model intercomparison project (MIP) results showing a good agreement. The difference of results of SDM and SN14 could be explained by the numerical diffusion and different performance of aerosol particles. The former is a numerical calculation error that is present in the simulation of SN14 but not in the SDM. SDM can simulate the motion and microphysical processes of aerosol particles more accurately, so it explicitly calculates the process of aerosol removal, and this would make the cloud holes larger and longer lasting. The results of this comparison also suggest that cloud-aerosol interactions could be critical to understanding the behavior and morphology of marine stratocumulus. We hope that our findings on the mechanisms of cloud-aerosol interactions will provide new insights for future studies and help us understand stratocumulus clouds.