Date

1996-07-15

Author

Oguz, T
MalanotteRizzoli, P

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The seasonal variability of the Black Sea circulation is studied using an eddy-resolving primitive equation model. A series of numerical experiments is carried out to determine the relative importance of wind stress, air-sea thermohaline fluxes, and river-induced lateral buoyancy forcing in driving the circulation on the monthly and seasonal timescales. A synthesis is made of the results with those obtained under yearly climatological conditions by Oguz et al. [1995] to assess whether the major circulation features are a response to the yearly forcings or are dominated by the seasonal cycle. The model experiments indicate that under all forcing mechanisms, the overall basin circulation is characterized by a very strong seasonal cycle dominating the yearly signal described by Oguz et al. [1995]. The purely wind-driven circulation reveals most of the observed circulation features including a well-defined meandering boundary current system and subbasin scale cyclonic gyres forming the interior flow structure of the basin. Topography obviously remains a crucial factor in controlling the pattern of the persistent rim current system all year long. The dynamical instabilities of the rim current produce strong meandering and mesoscale eddies which often modulate the basin and subbasin scale structures of the circulation. The surface thermohaline fluxes generate simpler circulation patterns with a comparable strength but mostly in the opposite direction to the wind-driven circulation. Two important by-products emerge from the present work. First is the necessity of reanalyzing the heat flux climatology. The existing surface thermohaline fluxes, even though not affecting critically the general characteristics of the surface circulation patterns, may induce rather unrealistic horizontal temperature distributions and water mass properties in the surface layer. Second, the role of the northwestern shelf in the cold intermediate water (CIW) mass formation process is shown to be secondary during moderate-to-high winter discharge conditions from the northwestern rivers. In these conditions the freshwater outflow reduces the density of the cold water formed on the shelf by about 1 kg/m(3) as compared with that of the basin interior, which is the major reservoir for the formation of the winter CIW.

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https://hdl.handle.net/11511/66042

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Graduate School of Marine Sciences, Article