On simulating high-frequency variability in Antarctic sea-ice dynamics models

Due to frequent and intense storm systems moving across the Antarctic sea ice, ice drift and deformation fluctuate substantially. Observations of drifting buoys show inertial power to be a substantial component of ice drift and deformation. Because the inertial period at high latitudes is close to tidal periods, this peak can be amplified due to resonance. In practice, the energy dissipation by ice interaction plays a significant role in dampening out this inertial energy. In present sea-ice dynamics models both with and without ice interaction, this inertial motion is overdamped due to the underestimation of coupling to the ocean boundary layer. To develop a more consistent treatment of ice drift under fluctuating wind fields, we consider here a vertically integrated formulation of the ice-ocean boundary-layer system that incorporates a more realistic treatment of the upper ocean. Under steady wind conditions this model reduces to the normal water-drag formulation used in most sea-ice dynamics models. Simulations using this "imbedded" model are analyzed to elucidate the role of ice interaction in the Antarctic ice-pack in modifying the high-frequency motion and inducing deformation which in turn significantly impact ice-thickness characteristics. The simulations demonstrate that in an interacting ice field in the presence of kinematic waves inertial imbedding can lead to oscillations in ice concentration of up to similar to 10% open water. These variations are similar in magnitude to observed deformation fluctuations in tide-free regions.