Baroclinic instability and transient features of mesoscale surface circulation in the Black Sea: Laboratory experiment

Abstract

The circulation in the Black Sea is characterized by a strong basin-wide current along the shore in the cyclonic direction (the Rim Current). Satellite and field data demonstrate that this circulation is subject to mesoscale variability in the form of meanders, eddies, and filaments. The unstable cyclonic boundary current was modeled in a new series of laboratory experiments on a rotating platform using a scaled model of the Black Sea. The dynamical similarity of the important dimensionless control parameters including the normalized Rossby deformation radius, the Rossby number, and the Ekman number was satisfied in the experiments. The results demonstrate the development of the baroclinic instability due to freshwater discharge imitating the river inflow in the Black Sea. The typical wavelength of the baroclinic instability observed in the experiments is analogous to that observed in the satellite images of the Black Sea when compared to characteristic dimensions of the basin. The cyclonic boundary current in the laboratory model is dynamically similar to the Rim Current. Persistent transient features of the circulation of the Black Sea, such as the so-called Batumi Eddy and the Sevastopol Eddy as well as other features, were reproduced in the experiments when the background rotation rate of the system was varied.