The sensitivity of the heat exchange at sea surface to meso and sub-basin scale eddies - Model study for the Black Sea

The heat exchange between the atmosphere and ocean (a function of the diffe rence between the sea surface temperature and atmospheric temperature) is d ifferently accounted for in numerical models, depending on their horizontal resolution. This could result in large differences in the rates of formati on of water masses in coarse resolution and eddy resolving models. We addre ss this issue in the present paper comparing simulations carried out with t he modular ocean model (MOM), which is set-up with coarse (1/4 degrees) and eddy (1/12 degrees) resolution. Both models are forced by atmospheric anal ysis data. The Black Sea is used as a test area, since it has well constrai ned heat balance. The absence of large open boundaries, which is not usuall y the case in most ocean models, precludes the dependency of the results on poorly known open boundary conditions and makes possible to accurately eva luate the model heat fluxes associated with mesoscale processes. We find ma ny indications that the transport and mixing associated with mesoscale eddi es provide an important mechanism for the penetration of cold surface water into the pycnocline. Their contribution is illustrated on the example of h eat exchange with the atmosphere and the resulting intermediate water mass formation, Two areas are investigated in more detail: the shelf edge/contin ental slope area, where the time averaged patterns of cooling are realistic ally simulated in eddy resolving models, and the area of anticyclonic circu lation between the coast and the main current the latter following approxim ately the continental slope. It is shown that the winter convection is enha nced at the periphery of coastal anticyclones. Lateral intrusions of coasta l waters into the pycnocline associated with eddies govern the characterist ics of cold intermediate water and the amplitude of annual signal at these depths. Statistical characteristics quantifying the contribution of mean ve rsus eddy part of the heat flux at sea surface in the two models are analyz ed. (C) 2001 Elsevier Science B.V. All rights reserved.