Realism of Lagrangian large eddy simulations: Tracking a pocket of open cells under a biomass burning aerosol layer

Abstract

An approach to improve the fidelity of Lagrangian large eddy simulation (LES) of boundary layer clouds is presented and evaluated with satellite retrievals and aircraft in-situ measurements. The Lagrangian LES are driven by reanalysis meteorology and follow trajectories of the boundary layer flow. They track the formation and evolution of a pocket of open cells (POC) underneath a biomass burning aerosol layer in the free troposphere. The simulations are evaluated with data from the Spinning Enhanced Visible and Infrared Imager (SEVIRI) on board the Meteosat Second Generation (MSG) satellite, and in-situ aircraft measurements from the Cloud-Aerosol-Radiation Interactions and Forcing (CLARIFY) field campaign. The simulations reproduce the evolution of observed cloud morphology, cloud optical depth, and cloud effective radius, and capture the timing of the cloud state transition from closed to open cells seen in the satellite imagery on the three considered trajectories. They also reproduce a biomass burning aerosol layer identified by the in-situ aircraft measurements above the inversion of the POC. We find that entrainment of aerosol from the biomass burning layer into the POC is limited to the extent of having no impact on cloud- or boundary layer properties, in agreement with observations from the CLARIFY field campaign. The simulations reproduce in-situ cloud microphysical properties reasonably well. The role of the model and simulation setup and the resulting uncertainties and biases are presented and discussed, and research and development needs are identified.