ON THE MECHANISMS OF THE BLACK SEA CIRCULATION

Abstract

Bryan's (1989) model is used in this study to simulate the circulation in the Black Sea. Wind stress, heat exchange, precipitation and evaporation at sea surface are prescribed from climatic data. River inflow and the inflow from the Mediterranean Sea are taken from observations. Two types of models are discussed: GCM with horizontal resolutionDeltalambda = 1°, Deltaphi = 0.5° and 12 levels; and EGCM with horizontal resolutionDeltalambda = 20',Deltaphi = 10' on the same levels. GCM is designed to study the role of the wind and buoyancy fluxes for the establishment of circulation. Model data shows that in the baroclinic experiments kinetic energy is less than in the barotropic experiment. This is a consequence of the formation of a strong halocline in the upper layer, where a substantial part of the energy input transforms into potential energy. The specific vertical stratification in the Black Sea restricts the penetration of seasonal signal into deep layers, and preconditions the establishment of a cold intermediate layer. Model data from EGCM shows that eddies contribute to some change in the transport mechanisms, compared to those in GCM. Seasonal forcing affects substantially the variability of the main Black Sea gyre. Comparisons between model and observational data indicate that models resolve the main features of the Black Sea circulation. They illustrate correctly physical processes in strong stratified geophysical fluids, and particularly in semi-enclosed basins, where precipitation and runoff exceeds evaporation.