A high-resolution coupled ice-ocean model of winter circulation on the bering sea shelf. Part I: Ice model refinements and skill assessments

Abstract

The Bering Sea Shelf transitions from ice-free to mostly ice-covered and back again over each winter. Sea ice coverage and the timing of ice melt play a critical role in determining shelf structure and consequently ecosystem response during the spring transition and summer. In this study, a 2-km resolution ocean model, which is based on the Regional Ocean Modeling System (ROMS) and was initially run and verified against a variety of observational data sources for summer 2009, is augmented with an ice model to study the coupled ice/ocean dynamics of the Bering Sea shelf from fall 2009 to summer 2010. Here we demonstrate that a single-category ice model is appropriate to describe seasonal evolution of the ice. Enhancements are made to the ice thermodynamic module and air/ice stress formulations to improve the match between the model and satellite microwave estimates of ice distribution and extent. The refined model accurately represents the timing and spatial extent of the spread of sea ice over the winter season as well as the ice retreat as it melts in spring and summer. Comparison with satellite products also suggests that the model captures the sea ice response on shorter temporal (∼O(days)) and spatial scales (∼O(20 km)). The modification to the drag formulation for example, can improve the modeled sea ice distribution in response to wind events overall and in particular in polynya regions along the coastlines of the Seward and Chukotka peninsulas and St. Lawrence Island.