A three-dimensional baroclinic eddy-resolving model of the Baltic Sea

Abstract

A three-dimensional eddy-resolving baroclinic model of the Baltic Sea is presented. The model comprises the whole Baltic Sea including the Gulf of Bothnia, the Gulf of Finland, Gulf of Riga as well as the Belt Sea, Kattegat and Skagerrak. With a horizontal resolution of 5 km and a discretization of 21 levels in the vertical, the general circulation and mesoscale dynamics as well as the exchange of water masses between North Sea and Baltic can be analysed. The model is forced by realistic wind fields computed from atmospheric surface pressure charts. Fresh water input due to river runoff is explicitly taken into account. At the surface, seasonal fluctuations of temperature and salinity are prescribed from a corresponding climatology. At the western boundary, an idealized North Sea basin is attached to the model domain. It is used to take up sea surface elevations in the area of the Skagerrak and to provide the water masses neccessary for the water mass exchange which have the characteristics of the North Sea. The three-dimensional initial fields of temperature and salinity were constructed from monthly mean maps of temperature and salinity and additional hydrographic measurements. Effects of vertical turbulent mixing are parameterized by using a vertical diffusion coefficient which is a function of the Richardson Number. The coefficient for horizontal diffusion of momentum is coupled with the relative vorticity. Results from different versions of the model (12/21 levels) are compared with hydrographic measurements taken during 1989 and 1992/1993. Generally, the correlation of the model solutions with the hydrographic observations is high. Most of the differences are due to uncertainties in the specified boundary conditions and forcing functions.