Dynamic coupling of sea ice and water for an ice field with free boundaries

Abstract

Ice-ocean dynamics is investigated using field data and a transient ice-ocean model. The measurements were made in April 1975 in the Bothnian Bay in an ice patch (100 km across) with free boundaries. The data consist of velocity time series of wind, ice, and currents at depths of 7, 10, 20 and 30 m from the ice. The ice-ocean model is used to examine the characteristics of the observations; the model consists of an unsteady free ice drift model and a transient Ekman flow model, which uses a two-equation turbulence model to achieve closure. For the surface wind at the altitude of 10 m, the estimated wind factor was 1.9%, and the deviation angle 21°, the ice-wind correlation being 0.90. The wind factor value is slightly low, probably due to biased wind data. The optimized oceanic boundary layer parameters are: roughness length 0.05 m and displacement height (due to ice ridge keels) 5 m. The model simulations predict significant inertial oscillations in the whole ice–ocean system, but in the ice measurements, they are missing and appear as highly damped in the current measurements. The reason for this discrepancy is probably due to the internal friction of the ice. Using the ocean model forced by observed ice drift data, a better fit to the current data was achieved and the inertial oscillations in the current calculations were correctly damped.