A coupled ice‐ocean mixed layer model of the marginal ice zone responding to wind forcing

A free‐drifting thermodynamic sea ice model is coupled with a continuously stratified ocean model, whose vertical mixing coefficients are determined by a turbulent closure scheme. The system has variability in the cross‐ice‐edge direction, while two‐dimensionality (along‐ice‐edge homogeneity) is assumed. The model is initially motionless and has no horizontal variability in ocean interior, whereas ice covers only a half portion. A uniform wind stress is imposed suddenly to drive the coupled system. The surface mixed layer is developed as time increases; i.e., a top few tens of meters are well mixed in a day. With an initial water temperature above a freezing point, the fresh mixed layer forms in the ice‐covered portion. A wind‐driven ice velocity is oriented to the right from the wind direction. A wind with the ice to the right (left) looking downstream produces upwelling (downwelling) under the ice edge caused by a difference in Ekman transport. An off‐ice (on‐ice) wind advects the ice toward the open water (ice‐covered) area, and makes the ice edge sharper (gentler) owing partially to faster movement in the region with higher ice concentration. In the off‐ice wind case, the mixed layer near the ice edge is shallower under development, so that a melt rate is smaller than that estimated by a prescribed‐depth mixed layer. An inertio‐internal gravity wave is generated by a transient variability in surface stress associated with a moving ice edge, most significantly in the case of the off‐ice wind, and enhances sharpness of the ice edge.