A Coupled Coastal Polynya–Atmospheric Boundary Layer Model

Abstract

This paper formulates and presents opening solutions of a one-dimensional coastal polynya flux model in which frazil ice is characterized by its depth and concentration. In comparison with polynya flux models in which variable frazil ice concentration is absent, this model is found to predict a smaller heat flux to the atmosphere. Consequently the model in this paper exhibits a wider steady-state polynya and longer opening times when compared with models in which ice concentration is neglected. The aforementioned polynya flux model is then coupled to a lower-atmosphere boundary layer model, and it is demonstrated that the polynya opening time and the steady-state width are significantly altered in the coupled, as compared with the decoupled, system. In essence, the heating of the lower atmosphere above the evolving polynya in the coupled system reduces the sensible heat flux between the ocean and atmosphere, thereby reducing the frazil ice production rate and hence leading to longer polynya opening time and wider steady-state width. This phenomenon is particularly noticeable when the potential temperature of the atmosphere at the coast is only slightly below the freezing point. In addition, a cutoff atmospheric wind speed is shown to exist, above which a steady-state polynya can never be obtained. Solutions calculated by the two models, using parameters representative of the St. Lawrence Island polynya, show that the new models contain substantial predictive capability.