Seasonal and interannual variability of the Black Sea eddies and its dependence on characteristics of the large-scale circulation

Mesoscale eddies in the Black Sea basin are investigated by automated eddy identification method (winding angle) using satellite altimetry data for 1992–2011. Seasonal and interannual eddy variability is strongly affected by the intensity of basin-scale circulation. Weakening of large-scale circulation in response to the decrease of the wind curl leads to the baroclinic instability of the Rim current and enhanced formation of mesoscale anticyclones. Increasing wind curl and circulation induce intensive formation of mesoscale cyclones. Intense developed large-scale circulation leads to the decrease in the number of both cyclonic and anticyclonic eddies. Eddies properties (orbital velocity, energy and lifetime) on the interannual time scales also depend on the intensity of the large-scale circulation. It was shown that the most powerful and long-lived anticyclones are generated in years with intense currents, right after the currents begin slowing down, which is related to the transfer of energy from large- to meso-spatial scales. Mechanisms of eddies formation and dissipation are discussed.