A grid refinement study of trade wind cumuli simulated by a Lagrangian cloud microphysical model: the super-droplet method

The impact of spatial resolution on the simulation of trade wind cumuli was investigated. The super-droplet method, an efficient stochastic Lagrangian cloud microphysical model, was used to reduce uncertainties due to the empirical parameterisation of cloud microphysics and numerical diffusion for advection, which is inevitable in an Eulerian cloud microphysical model. We showed for the first time that cloud cover numerically converged with a grid resolution of 12.5 m. Our grid refinement analysis elucidated a significant contribution of small cumulus clouds to total cloud cover, as such cumuli are generated by small-scale updrafts that can be resolved only at a fine resolution.