Polynyas in a high-resolution dynamic-thermodynamic sea ice model and their parameterization using flux models

Abstract

This paper presents an analysis of the solutions for a steady state latent heat polynya generatedby an applied wind stress acting over a semi-enclosed channel using: (a) a dynamic–thermodynamicsea ice model, and (b) a steady state flux model. We examine what processes in the seaice model are responsible for the maintenance of the polynya and how sensitive the results areto the choice of rheological parameters. We find that when the ice is driven onshore by anapplied wind stress, a consolidated ice pack forms downwind of a zone of strong convergencein the ice velocities. The build-up of internal stresses within the consolidated ice pack becomesa crucial factor in the formation of this zone and results in a distinct polynya edge. Furthermore,within the ice pack the across-channel ice velocity varies with the across-channel distance. It isdemonstrated that provided this velocity is well represented, the steady state polynya flux modelsolutions are in close agreement with those of the sea ice model. Experiments with the sea icemodel also show that the polynya shape and area are insensitive to (a) the sea ice rheology;(b) the imposition of either free- slip or no-slip boundary conditions. These findings are usedin the development of a simplified model of the consolidated ice pack dynamics, the output ofwhich is then compared with the sea ice model results. Finally, we discuss the relevance of thisstudy for the modelling of the North Water Polynya in northern Baffin Bay. DOI: 10.1034/j.1600-0870.2001.00113.x