Evaluating Lagrangian Large Eddy Simulations of a Pocket of Open cells with Satellite and In-situ Data

Pockets of open cells (POCs) are regions of broken, precipitating stratocumulus clouds embedded into an overcast stratocumulus cloud deck with little or no drizzle. Owing to their low cloud fraction, POCs have a reduced cloud shortwave radiative effect compared to the surrounding stratocumulus cloud. POCs can persist for several days, but respond to meteorological and microphysical (aerosol) controls. We evaluate a Lagrangian large eddy simulation (LES) of a POC that was observed in the South-East Atlantic during the Cloud Aerosol Radiation Interactions and Forcing field campaign (CLARIFY) with MODIS and SEVIRI satellite and CLARIFY in-situ data. The LES are driven by ERA5 reanalysis data and follow the POC for two days along HYSPLIT trajectories. The LESs reproduce satellite cloud properties (optical depth, effective radius, and liquid water path) reasonably well, with deviations outside the retrieval uncertainty likely arising from limited vertical resolution and potentially retrieval biases in broken cloud situations. Cloud organization as observed by MODIS is reproduced well. The LESs reproduce ERA5 boundary layer temperature and moisture profile in before onset of precipitation, but exhibit a cold and dry bias in the presence of precipitation relative to ERA5 and the CLARIFY in-situ data. We test the sensitivity of the simulations to vertical resolution, assumptions in the cloud microphysics scheme (width of cloud and rain drop size distribution, sedimentation velocity, and microphysical kernel), and discuss satellite retrieval uncertainties in broken cloud situations.