On the Black Sea water mass formation. Model sensitivity study to atmospheric forcing and parameterizations of physical processes

Abstract

A numerical model of the Black Sea circulation is developed using the Bryan-Cox-Semtner modular ocean model. Some available climatic and atmospheric analysis data are used to force the model. The analysis of the simulations gives a strong motivation to construct new sea surface forcing functions for this basin. It is shown that they provide heat and water fluxes that are consistent with the observations and with some independent balance estimates. The improved model forcing results in simulating of a realistic circulation. The inflow through the Strait of Bosphorus is parameterized using physical concepts, based on theoretical models and observational data, relating the strait exchange to the net fresh water flux at sea surface. A new parameterization is included to simulate the Mediterranean plume. The model sensitivity to driving forces, physical processes, and different parameterizations is studied. The results are used to tune the model to simulate adequately the water mass formation. The most sensitive elements of the vertical stratification, as the cold intermediate layer and the deep temperature intrusions, are used in this tuning. The model circulation, ventilation of the deep and intermediate layers, some characteristic time and length scales show a good agreement with the observations. The cooling capacity of the intermediate water is analysed as dependent on the fresh water flux at sea surface. The model simulations give indications that the changes in thermal stratification in the intermediate depths are indicative not only for how severe the preceding winter was. These changes are also dependent on the variability in the fresh water. In a long run, they could illustrate climate changes in the catchment area of the Black Sea rivers.