Modelling the Baltic Sea as thirteen sub-basins with vertical resolution

A mathematical model of the Baltic Sea is presented and explored. The model divides the Baltic Sea into 13 sub-basins. The dynamics in each sub-basin is reduced to a one–dimensional boundary layer problem with vertical mean velocities based upon in- and outflows from surrounding basins. The turbulent exchange coefficients are calculated using a two-equation model of turbulence. The boundary conditions consider wind stress as well as the heat exchange between water and air. Sea ice is neglected in the model; instead, the water temperature is kept at the freezing point when the temperature is below freezing. The model is tested against observations from the severe sea ice winter 1986/87 and found to simulate the surface water temperature reasonably in all sub-basins during the whole winter. The thermal response due to sea ice has, however, to be considered in some sub-basins, particularly during spring warming.