Physical mechanisms of submesoscale eddies generation: evidences from laboratory modeling and satellite data in the Black Sea

Abstract

The observed evidence of the implementation of three different mechanisms of the submesoscale eddies generation in the Black Sea previously studied by the field research and laboratory modeling is presented. These mechanisms are the following: (1) horizontal shear instability of the surface current; (2) flow separation behind capes and peninsulas; (3) spatial heterogeneity of the wind blowing from the coast to the sea. The first mechanism is implemented both in the open sea and in the coastal zone. The other two operate in the coastal zone. It was found that with the implementation of each from these mechanisms an asymmetry in the formation of cyclonic and anticyclonic eddies arises. Particularly, as a result of the flow shear instability, cyclonic vortices are usually observed, anticyclones are formed only in the case of rather weak anticyclonic velocity shear. Due to the alongshore current separation behind capes and peninsulas, the anticyclonic eddies and even the chains of this kind of eddies are predominantly formed. The spatially inhomogeneous wind from the coast to the sea generates eddy dipoles with dominating anticyclones. The joint analysis of surface geostrophic currents calculated using satellite altimetry data, the wind velocity field over the sea (reanalysis data), and satellite images in the optical spectral range for various regions of the Black Sea confirmed the main results of laboratory experiments and field research.