Intercomparison of cloud model simulations of Arctic mixed-phase boundary layer stratus observed during SHEBA

A long-lived, precipitating, low-level, mixed-phase boundary layer cloud observed during the Surface Heat Budget of the Arctic Ocean (SHEBA) experiment is used as a case study for intercomparison of six cloud-resolving and large-eddy simulation models. This case occurred during relatively polluted conditions over pack ice in the central Arctic, in contrast to the pristine, open ocean conditions for the previous Mixed-Phase Arctic Cloud Experiment (MPACE) model intercomparison study. A brief overview of the case will be presented along with detailed results from the model simulations. In addition to the baseline simulations, sensitivity tests with varying ice nucleus/ice crystal (IN) concentrations and cloud condensation nucleus (CCN) concentrations will be shown. Overall, there are large differences among the models in terms of cloud phase, condensed water path, and surface radiative fluxes, with several models able to simulate long-lived mixed-phase clouds and others producing rapid glaciation and conversion to all-ice clouds. The simulation of either mixed-phase or all-ice clouds has important consequences for the surface radiative fluxes, cloud dynamics, cloud top radiative cooling, and boundary layer structure. All models exhibit significant sensitivity to the IN concentration, but the nature of this sensitivity differs among the models. There is much less sensitivity to CCN, for the range of CCN concentrations tested. Finally, various relationships (e.g., ice water content and mean ice particle fallspeed, ice water content and vapor depositional growth) are compared among the models, and with available observations, to elucidate causes of the differences in the simulations.