Mean circulation and water exchange in the Gulf of Finland — a study based on three-dimensional modelling

A three-dimensional baroclinic prognostic model has been applied to study the mean circulation and its persistency as well as the water exchange in the Gulf of Finland. A five-year simulation for 1987–1992 was carried out using a nested grid approach, where a high-resolution sub-model of the Gulf of Finland was forced at the open boundary by a larger-scale Baltic Sea model. Realistic meteorological forcing for the period under study was used. The overall results of the investigation showed that the mean circulation pattern was complex with numerous meso-scale eddies, although a cyclonic mean circulation generally is discernible. The mean surface circulation of the Gulf was found to take place in the form of a strong outflow adjacent to the Finnish coast compensated for by an inflow at the Estonian coast, a circulation which is highly dependent on depth. The outflow on the northern side of the Gulf proved to be a distinct feature with a persistency ranging between 50% and 80%. The water exchange between the Gulf and the Baltic Proper appears to be stronger than previously estimated. It was found that ordinary budget estimates of water exchange (based on calculating the amount of in- and out-flowing water) do not give much relevant information concerning the Baltic Sea Proper–Gulf water exchange since these straightforward estimates do not reflect the internal dynamics of the Gulf of Finland.