Formation of ice bands by winds

A mechanism for the formation of ice bands is proposed as a coupled response of ice edge and lee waves to wind under the hydrostatic approximation. A high-resolution ice-ocean coupled model is used in an x-z domain with grid sizes (x, z) = (250 m, 1 m). Under an along-ice-edge wind, such that the Ekman transport is away from the ice edge, the nearly discontinuous surface stress between the ice-covered and open seas generates lee waves. A thin layer of high-potential vorticity fluid under the ice is produced by the Ekman forcing, enabling the ice edge to rapidly slip over less stratified water. This is favorable for supercritical conditions when lee waves are generated. Ice bands are formed by the corresponding convergences and divergences. The flow becomes subcritical farther behind the ice-edge but secondary lee waves and ice bands form because of the secondary stress discontinuity behind the lead ice band. An analytical solution is derived to show that ice bands have longer widths than the lee-wavelengths because the ice-ocean stress creates the smoothing effect. Vertical motions associated with the lee waves have speed of the order of 10 m/day, extend to the bottom (300 m), and contribute to deep vertical mixing and the subsequent melting of the ice. These small-scale features are not modeled well with horizontal grids coarser than approximately 2.5 km.