Sensitivities of a simulated Arctic stratocumulus to aerosol and microphysical parameters

Low-level, mixed-phase clouds are a key component of the Arctic energy budget and can impact the extent and thickness of sea ice. These clouds are influenced by aerosols and microphysical processes that can determine the phase partitioning and thereby cloud lifetime and radiative impacts. Atmospheric models often struggle to represent phase partitioning in Arctic mixed-phase clouds correctly. Aerosol number concentration (ANC), aerosol type (Atype), ice crystal number concentration (ICNC), and ice crystal morphology (ice crystal habit; IChab) have previously been shown to impact phase partitioning in Arctic clouds. In this study, we quantified the relative importance of these parameters for simulated liquid water path (LWP), ice water path (IWP), and downward longwave radiation at the surface (DWLW) of a slightly supercooled Arctic mixed-phase cloud by applying factorial analysis. Using MIMICA, the MISU-MIT Cloud Aerosol large-eddy simulation code, we found that ANC was the most important parameter for LWP and DWLW, while ICNC controlled IWP. IChab ranked third for all simulated variables, yet it crucially determined the final phase state of the cloud. The impact of Atype was negligible compared to the other three parameters. Recognizing the limits of relying on a single case study and model, our results suggest that future Arctic field campaigns should prioritize observations of ANC, ICNC, and, crucially, ice habit for slightly supercooled mixed-phase clouds. Models must also represent different ice habits to accurately simulate cloud phase partitioning and its subsequent impact on the Arctic energy budget.