The present paper represents the results of two experiments on numerical modeling (within the framework of the two-layer eddy-resolving model) of the Black Sea large-scale circulation under the influence of the seasonally-variable wind. The actual bottom topography is taken into account in the model. The motion is excited only by the tangential wind stress with a non-zero vorticity. The energy loss is due to the bottom friction, the friction at the layers' interface and the horizontal turbulent viscosity. In one of the experiments under consideration, the wind stress vorticity changes its sign depending on the season (in winter it is cyclonic, in summer-anticyclonic), but remains constant in space. In the other experiment, the field of the tangential wind stress is preset (according to the modern notions on its spatial variability) in such a way that over the sea western half there is the zone of anticyclonic vorticity, the area and intensity of which vary throughout the year. In both cases, the circulation in the Black Sea is periodically divided into two large cyclones-the "Knipovich glasses". However, due to the western intensification of currents caused by the β-effect, the wind stress with spatially uniform vorticity results in formation of a cyclonic cycle of extremely high intensity in the southwestern part of the basin. In the other experiment that takes into account spatial variability of the wind stress vorticity above the sea, namely, anticyclonic vorticity of the wind tangential stress over the basin western part, the obtained circulation quite corresponds to the observational data.
Marine Hydrophysical Institute of RAS , Sevastopol, Russian Federation * pavlushin@mhi-ras.ru Purpose. The present article is aimed to carry out the energy analysis of the numerical experiment results obtained from modeling of the large-scale circulation in the Black Sea within the framework of a two-layer eddy-resolving model under the tangential wind stress forcing, and also to determine directions and magnitudes of the energy transitions accompanying formation of the large-scale flows and mesoscale eddies in the sea. Methods and Results. The analysis is carried out for the period of statistical equilibrium in which the average values of all the characteristics calculated in the model remain constant in time. According to the motion scales, the Reynolds averaging method permits to divide the energy characteristics (mechanical energy and its transitions) into those relating to the large-scale flows andto the eddies. The large-scale currents are defined as average flows over a certain selected time interval, and the deviations from them are considered to be the vortices. The energy characteristics averaged over time and/or space, are analyzed. For the period of statistical equilibrium, calculated are the energy diagrams showing contribution of the large-scale currents and the vortices to the total mechanical energy, to the magnitudes and directions of energy transitions. The time-averaged fields both of the energy components and the forces involved in the energy balance were constructed for the same period. Conclusions. It is shown that baroclinic instability of a large-scale flow is the main cause of the Rim Current meandering, and the energy is transferred to the bottom layer due to baroclinic instability of the eddies. It has been revealed that a large portion of wind energy falls on the eastern part of the sea, whereas the energy losses take place in the western and northwestern regions of the basin. The basic part of energy dissipation takes place due to the friction forces' work on the lower boundary of the upper layer in the area where the layer interfaces intersect the bottom.Keywords: kinetic energy, available potential energy, energy balance, numerical model, the Black Sea, energy diagram, eddy-mean flow interactions.Acknowledgements: the research is carried within the state task on theme No. 0827-2018-0002 "Development of the methods of operational oceanology based on the interdisciplinary studies of the marine environment formation and evolution processes and mathematical modeling using the data of remote and direct measurements".
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