A numerical study of ice-drift divergence by cyclonic wind with a Lagrangian ice model

In polar regions low-pressure systems drive sea ice divergence, which can accelerate summer sea ice melt through energy absorption at resulting open water areas. This paper examines the mechanisms that cause the ice divergence and its seasonal change with a Lagrangian ice model. We focus on the effects of initial ice concentration, ice strength and ocean stratification. A series of idealized simulations (initially at 5 km resolution) are carried out with a Rankine combined vortex as external wind forcing. We have found a characteristic length scale r^*₁ in free drift, based on the influence of the Coriolis term. The results show that ice concentration decreases most greatly within the range of r^*₁. In addition, ice divergence becomes small in the inner region for high concentrations (i.e. over 0.95), due to inward internal force blocking divergent deformations. The effects of ocean stratification on ice-drift divergence are also examined. Numerical results show that as the density stratification increases divergent Ekman flows beneath ice further promote the ice-drift divergence and lead to more reduction in the ice concentration through thinning of surface Ekman layer.