A dynamical model for wind‐driven ice motion: Application to ice drift on the Labrador Shelf

Abstract

A three‐dimensional coupled ice‐ocean model has been developed to study short‐term ice motion over the eastern Canadian continental shelf. The model consists of a Hibler ice model and a diagnostic ocean model. Ice is coupled to the ocean through a surface Ekman layer. The model is implemented for the Labrador Sea using 6‐hourly winds and atmospheric pressures as input forcings. The results show that the model is able to produce many desired features of ice motion and ocean currents including wind‐generated coastal currents, an ice velocity field reflecting the influence of permanent and transient currents, and an increased sea surface tilt and ice internal stress at the coast. The model is used to simulate ice drift trajectories from six ice beacons deployed over the Labrador and Newfoundland Shelves in 1992. In the subtidal frequency range the modeled and observed ice velocities are in excellent agreement. Model errors, measured by the rms separation between the modeled and observed positions, increase with time. The increase is 10 km d−1 in the first 2 days and slower after 2 days. The model results are compared with a model run without ice‐ocean coupling and a calculation using an empirical relationship and parameters (speed ratio and turning angle). The errors are 20% (no ice‐ocean coupling) and 70% (empirical relationship) larger than the errors in the coupled model in the first 2 days and much larger after several days.