On the modelling of ice-thickness redistribution

An ice-thickness distribution model based on physical ice classes is formul ated. Pack ice is subdivided into open water, two different types of undefo rmed ice, and rafted, rubble and ridged ice. Evolution equations for each i ce class are formulated and a redistribution between the ice classes is cal culated according to a functional form depending on the ice compactness, th ickness and velocity divergence. The ice-thickness distribution model has b een included in a coupled ice-ocean model, and numerical experiments have b een carried out for a simulation of the Baltic Sea ice season. The extended ice classification allows separation of thermally and mechanically produce d ice. Inherent thermodynamic growth/melting rates of the ice classes can b e introduced into the model, giving a more detailed seasonal evolution of t he pack ice. In addition, the model provides more information about the sur face properties of pack ice. Numerical experiments for the Baltic Sea show that both the sub-basin and i nter-basin ice characteristics were realistically simulated by the model. D eformed-ice production was related to storm activity. Most of the deformati on was produced in the coastal zone, which is also an important region for thermodynamically produced ice because of the ice growth in leads. The mode lled mechanical growth rates of ice were 0.5-3 cm d(-1) on a basin scale, c lose to the thermodynamic :ice-production rates. The deformed-ice fraction was 0.2 in mid-winter and increased to 0.5-1.0 during spring.