A numerical model of the atmospheric boundary layer over a marginal ice zone

Abstract

A two‐dimensional, multilevel model for simulating changes in the atmospheric boundary layer across a marginal ice zone is described and applied to off‐ice, on‐ice, and along‐ice edge wind conditions. The model incorporates a second‐moment closure for parameterizing the intensification and suppression of turbulent mixing in the boundary layer due to stratification effects. For off‐ice winds, as the atmospheric boundary layer passes from cold smooth ice onto warm open water, the onset of intense convection raises the inversion. Over the transition zone of rough rafted ice with open leads, the shear stress on the ice cover increases significantly before dropping down to the downstream values over water. Such nonmonotonic surface stress could be the cause of divergence of sea ice near the ice edge in a marginal ice zone. These results are in agreement with the one‐layer model simulations of off‐ice winds by Overland et al. (1983). For on‐ice wind conditions, as the warm flow in the boundary layer encounters the cold ice conditions, the resulting stable stratification could rapidly suppress the turbulence in the boundary layer, leading to the development of a shallow inversion and an associated jet. When the wind is predominantly along the ice edge, the temperature contrast between the open water and the ice could produce a thermal front at the ice edge in the boundary layer with strong associated turbulence. More observations are needed to verify these model predictions. Nevertheless, these model results suggest that it is important to account for the changes in the characteristics of the atmospheric boundary layer across the marginal ice zone in our attempts to understand the behavior of the ice cover in these regions.