SIMULATING THE BALTIC SEA-ICE SEASON WITH A COUPLED ICE-OCEAN MODEL

The Baltic Sea ice season climatology is studied with a coupled ice-oc ean model, The evolution of sea temperature, ice thickness and ice dri ft has been simulated for three particular ice seasons, normal (1983/8 4), severe (1986/87) and mild (1991/92), forced with the prescribed da ily atmospheric data. The ice model is a plastic Hibler model with a t hree-level ice thickness distribution (open water, undeformed ice and ridged ice) and thermodynamics. The ocean model consists of a barotrop ic circulation model with 4-layer vertical thermodynamic evolution. Th e models are coupled via the momentum and heat fluxes; the grid size i s 10' in latitude and 20' in longitude. With the same initial conditio ns and observed meteorological forcing, a fully prognostic thirteen-mo nths integration was performed for each ice season from 1 May to 31 Ma y in the following year. The model results were compared with routine ice charts. The annual cycles of sea surface temperature, ice thicknes s and coverage, and the interannual variability of the ice seasons wer e realistically simulated. Ocean surface temperatures were produced we ll in the shallow sea areas, but over the deeper central parts of the basins they were too warm in the winter stage. On the average and seve re winters the predicted maximum ice extent was about 20% less than th at observed, while in the mild winter the agreement was very good. Bas in scale features were rather well realized in the ice thickness field . The freezing date and ice growth were in agreement with observations , but the beginning of the ice melting was delayed which led to about 1-2 weeks delay in the ice break-up date.