The role of plastic ice interaction in marginal ice zone dynamics

Abstract

Under appropriate conditions, the nonlinear nature of plastic ice interaction together with a nonlinear coupling between ice thickness characteristics and ice rheology can substantially modify the character of marginal ice zone dynamics. This paper examines the steady state ramifications of these nonlinearities by using a one‐dimensional simplification of Hibler's (1979) two‐level viscous plastic sea ice model. A series of idealized small‐scale simulations (4‐km resolution) are carried out with the model formulated in a moving Lagrangian grid in order to remove diffusion effects. Analytic solutions for the equilibrium plastic adjustment case are also constructed. The results show that if the ice thickness distribution is allowed to equilibrate in response to a constant wind field, the thickness strength coupling will yield a sharp ice edge, with the compactness dropping rapidly to zero near the ice margin. Despite this compactness falloff, the steady adjusted ice velocity is nearly constant across the marginal ice zone. However, the adjustment to a steady state constant velocity can be preceded by a period of shearing, which will abate as the ice strengthens by ridging. With an increase in forcing near the edge, the ice velocity scales with the wind velocity but with a speed less than free drift. In the absence of water drag and wind stress the model exhibits a very slow outward creep but yields no ice edge jet effects. The ramifications of plastic interaction on upwelling and downwelling are also examined. With the same drag coefficients over ice and ocean, and for a north‐south ice edge, the model yields (in the northern hemisphere) upwelling for northward winds, downwelling for southward winds, and no effect for off‐ice winds.