Comparison of hydrodynamical models of the Gulf of Finland in 1995: a case study

Three-dimensional hydrodynamic models of the Gulf of Finland, namely Finnflow and Finest, have been compared with observations of salinity, temperature water levels and currents in 1995. The Finnflow model had a vertical co-ordinate system with fixed levels whereas in the Finest model a modified sigma co-ordinate system was used. The model results were also compared with each other. Both models were able to reproduce the main spatial east–west gradient of salinity, the temporal variability of temperatures in the uppermost layers and the height variations of water levels. Problems were caused by the inaccuracies of the open boundary conditions. The verification of the models with current measurements gave less satisfactory results, mainly due to the too coarse horizontal resolution of the models. The accuracy of the near-bottom salinity and temperature suffered from inaccuracies in the open boundary condition and related problems in defining the stratification conditions in the Gulf. The Finnflow model described better up- and downwellings, while the stratification conditions were more accurately described by the Finest model. These differences are probably best explained by the different co-ordinate systems in the models.