First results of multi-year simulations using a 3D Baltic Sea model.

Typ: Rapport
Serie: RO 27
Författare: H.E. Markus Meier


Results of 13-year hindcast simulations for the period 1980-1993 are presented using a 6 nm version of RCO (the Rossby Centre Ocean model). The coupled ice-ocean model for the Baltic Sea with open boundary in northern Kattegat is forced with realistic atmospheric forcing and river runoff. The results are compared to monitoring temperature and salinity profile data, mean sea surface height, ice extent and ice thickness data. The model performance is regarded as good. For example, erosion of the halocline in the Baltic proper could be avoided due to carefully chosen parameterizations. However, it is necessary to extend the model domain, to embed a bottom boundary layer model (or to increase horizontal resolution) and to include more ice classes.

Furthermore, a set of sensitivity and process oriented studies are performed to increase our understanding of the processes involved. Thereby, different mixing parameterizations, advection schemes and open boundary data are tested. Experiments with and without wind, present day and increased runoff, with and without ice or with and without ice dynamics are compared and analyzed. The results show that the mean wind-driven circulation affects mean SST's and SSH's. Mean Ekman transport is added to the thermohaline vertical circulation causing a 3-layer transport system into the Gulf of Finland for example. Mean surface heat flux pattrns are affected by horizontal advection, up- and downwelling and ice cover. Without ice heat loss in ice covered areas is increased tremendously. Ice dynamics re-distribute mean ice thickness and concentration from south-westem to north-eastern parts in the Gulf of Bothnia. Increased river runoff causes a decrease of surface layer salinity and halocline depth in Gotland Basin. In Bornholm Basin mainly lower layer salinity is affected indicating reduced salt water inflow through the Danish Straits.