Sensitivity of an August 2022 Arctic Cyclone to Sea Ice and Ocean Representation in Polar WRF

The ability to resolve interactions between Arctic cyclones (ACs) and sea ice is expected to be important in forecasting ACs, and the dynamical processes and physical mechanisms underlying these interactions are not fully understood. The boundary between sea ice and open ocean is typically associated with low-level baroclinicity, which can be an important ingredient for Arctic cyclogenesis. Furthermore, the spatial distributions and properties of sea ice affect the spatial variability and magnitude of surface turbulent sensible and latent heat fluxes (hereafter referred to as surface fluxes), and these fluxes affect low-level diabatic heating patterns that modulate Arctic cyclogenesis. In the marginal ice zone, wind and waves from ACs can redistribute fragmented sea ice. The resulting sea-ice rearrangement influences distributions of surface fluxes and low-level baroclinicity, thereby affecting the boundary-layer structure of ACs. An improved understanding of the interactions between ACs and sea ice may contribute to improvements in the ability to forecast ACs in the presence of these interactions.

The purpose of this presentation is to investigate the sensitivity of AC structure and evolution to surface boundary conditions in the polar-modified Weather Research and Forecasting Model (i.e., Polar WRF). Specifically, a range of model specifications for the treatment of ocean temperature and sea-ice concentration (e.g., whether these fields are static or updated) is used to explore the influence of these quantities on a simulated AC. This presentation focuses on an AC case on 15–27 August 2022, which was observed near Svalbard during the Office of Naval Research’s THINICE campaign on 5–25 August 2022. The 15–27 August 2022 AC represents an archetypal case, which includes a nearby upper-level trough, cold-core structure, frontal features, a low-level jet, and movement of the AC over sea ice.

AC intensity, boundary-layer features such as surface fronts and low-level jets, and surface flux distributions are compared across simulations with different treatments of ocean and sea-ice conditions. The control simulation uses static sea-surface temperature and sea-ice data from the ERA5. Experimental simulations utilize the built-in ocean model in Polar WRF and sea-ice fields from the Operational Group for High Resolution Sea Surface Temperature Level-4 dataset, and the ocean and sea-ice conditions are updated over time. Polar WRF uses ERA5 data for initial and boundary conditions in all simulations. Where possible, observations are used to assess the validity of simulated AC structure and surface fluxes.