The boundary layer and cloud field associated with marine cold air outbreaks (MCAOs) in the COMBLE observations and the SCREAM DYAMOND2 simulation

Marine cold-air outbreaks (MCAOs) occur in the high-/mid-latitudes when cold polar or continental air masses move equatorward onto warmer oceans. It is challenging to represent the atmospheric boundary layer and clouds associated with MCAOs in numerical models including convection-permitting models (CPMs), because the scales of the shallow convection and the related mixed phase microphysical processes are much finer than the effective resolution of these models. Specifically, models struggle to correctly capture the mesoscale variability of the cloud fields and tend to underestimate the cloud fraction and cloud liquid water in the stratocumulus cloud region of MCAOs. In CPMs, the simulated stratocumulus clouds and their transition are found to be sensitive to the choices of the turbulence scheme and the ice/snow treatment in the microphysics scheme. The Energy Exascale Earth System Model (E3SM) project is developing a new global CPM called the Simple Cloud-Resolving E3SM Atmosphere Model (SCREAM) with globally uniform 3.25 km grid spacing. SCREAMv0 model has successfully conducted a 40-day global simulation (Jan 20-Mar 1, 2020) as part of the second GCPM intercomparison called DYnamics of the Atmospheric general circulation Modeled On Nonhydrostatic Domains (DYAMOND2). Based on the observations from the ARM COMBLE field campaign, satellite retrievals and the reanalyses data, we will evaluate SCREAMs performance in simulating the mesoscale variability of the marine boundary layer cloud over the COMBLE region associated with MCAOs. Focusing on an MCAO event between Feb 22 and Feb 27, 2020, we will analyze the transition of the PBL structure, the cloud microphysics properties and the cloud mesoscale morphology along the main air flow in the observations and in the SCREAM simulation. The results will lead to a better understanding of the physical processes controlling the cloud transitions during MCAOs in SCREAM. Acknowledgement: This work is supported by the ASR Program for the Office of Science of the U.S. DOE. This work was performed under the auspices of the U.S. DOE by LLNL under contract DE-AC52-07NA27344. LLNL-ABS-821839