Modeling the seasonal, interannual, and long-term variations of salinity and temperature in the Baltic proper

Salinity and temperature variations in the Baltic proper and the Kattegat h ave been analyzed with a numerical ocean model and a large amount of observ ational data. In the model, the Baltic Sea is divided into 13 sub-basins wi th high vertical resolution, horizontally coupled by barotropic and barocli nic flows and vertically coupled to a sea-ice model which includes dynamics as well as thermodynamics. The model was integrated for a 15-year period ( 1980-1995) by using observed meteorological forcing data, river-runoff data and sea-level data from the Kattegat. The calculated 15-year median profil es of salinity and temperature in the different sub-basins are in good agre ement with observations. However, the calculated mid-depth salinities in th e Arkona Basin and Bornholm Basin were somewhat overestimated, and the calc ulated deep-water temperatures in the Arkona Basin and the Bornholm Basin a re somewhat lower than the observed values. Frontal mixing and movements in the Kattegat and the entrance area of the Arkona Basin were important to c onsider in the model. Water masses were simulated well, and prescribing con stant deep-water properties in the Kattegat proved to be a reasonable later al boundary condition. Further, comparisons were made between observed and calculated seasonal and interannual variations of the hydrographic properti es in the Eastern Gotland Basin, as well as the interannual variations of t he annual maximum ice extent. We conclude that the model can simulate these variations realistically. The major Baltic inflow of 1993 was also simulat ed by the model, but the inflowing water was 1-2 degrees degrees too cold. Finally, the response times to changes in forcing of the Baltic proper and the Kattegat were investigated by performing the so-called lock-exchange ex periment. Typical stratification spin-up times were of the order of 10 year s for the Kattegat, and 100 years for the Baltic proper.