Impact of the Novorossiysk Bora on the Upper Layer of the Black Sea

The structure of atmospheric fields during the bora and the response of the sea to the strong Novorossiysk bora on February 7-8, 2012 have been simulated with the WRF-NEMO coupled numerical model with a resolution of 1 km. Development of strong air currents over the lee side of the Caucasus Mountains and a temperature rise in the atmosphere over the coastal part of the sea are noted. The parameters that deter mine the features of the bora development are estimated. The perturbations of temperature fields in the sea are analyzed. It is shown that the response of the sea surface temperature field to the wind impact was spatially heterogeneous: during two days of the bora, the water temperature decreased near the Caucasian coast and, on the contrary, increased further off the shore. A cause for such heterogeneity is considered. It is shown that the development of deep penetrating convection started about 0.5 days after the bora onset. As a result of the bora passage, the temperature at the depth of similar to 40 m, where the layer of the warmer water that remained from the summertime upper quasihomogeneous layer was situated, dropped by 1-1.5 degrees C, and the thickness of the quasihomogeneous layer increased by two times, up to 60 m. The changes in the temperature and thickness of the quasihomogeneous layer resulted from the entrainment of the warmer water from underlying levels and the cooling due to sensible and latent heat fluxes from the sea surface. A characteristic effect of the bora development is analyzed, namely, a mesoscale quasi-two-dimensional vortex in the atmosphere over the southeastern part of the sea, which is associated with the features of the air flowing around the northwestern edge of the Caucasus Mountains. A response of the sea to this vortex is considered.