A Case Study of Marine Cold Air Outbreaks with the Simple Convection-Permitting E3SM Atmosphere Model

Marine cold air outbreaks (MCAOs) and their associated planetary boundary layer (PBL) and cloud fields pose a challenge for numerical models, including kilometer-scale models like the DOE global Simple Cloud-Resolving E3SM Atmosphere Model (SCREAM), because the scales of the shallow convection and the related mixed phase microphysical processes are much finer than the effective resolution of these models. In this study, we evaluated SCREAM's performance in simulating mesoscale variability and cloud phase partition during an intense MCAO event over the COMBLE region using satellite and ARM observations. We found that SCREAMv0 tends to overestimate cloud ice water within a cloud temperature range of −30^oC - −15 ^oC, which is much higher than the typical temperature for homogeneous freezing (≤ −38^oC). While the cloud liquid water in the cumulus cloud regime tends to be underestimated, the ice clouds are overestimated and strongly linked to the model resolved updrafts. However, due to the limited model output variables from the global SCREAM simulation, we could not fully understand mechanism underlying the simulated cloud phase transition.

To better understand the mixed-phase cloud processes simulated by SCREAM, we conducted the COMBLE case study and participated in the intercomparison modeling study of the COMBLE cases. Our goal was to investigate how prescribed aerosol and simplified mixed-phase cloud microphysical processes impact cloud transition in the Doubly Periodic mode of SCREAM (DP-SCREAM), which is much more computationally efficient than the global SCREAM for model process-level studies. We will present DP-SCREAM results about the factors controlling the efficiency for the liquid-to-ice transition in mixed-phase clouds simulated by SCREAM, including different Ice Nuclei (IN) conditions, cloud ice particle nucleation and cloud-ice collision efficiency, and large-scale condition. We will use ARM cloud observations during the COMBLE field campaign, supplemented by satellite retrievals from MODIS, CloudSat and CALIPSO, as observational references to assess the modeled physical processes.

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-848721