The Barotropic Instability of the Oceanic Jet Currents

Abstract

In this article we present the results of the laboratory experiments with shift currents in the homogenous shallow water generated by differentially rotating elements of the vessel bottom: central axisymmetric disk and outer coupled rings. Based on the experimental results, we explain the generation of vortex rings due to the development of barothropic or shift instability of currents. We show that the surface of the differentially rotating liquid in the horizontal rate shift zone creates the conditions for generating chains of vortices rotating clockwise. When changing the values of rate shift and the rotation rate of the whole system, the formation of modes of instability of vortex structures is observed, the conditions for which were quantified on the laboratory current stability diagram in Rossby and Ekman numbers. To interpret the experimental data we considered the solutions of the equations for quasi-two-dimensional geophysical currents in the form of elementary waves of the current function disturbance. We estimated the parameters of the perturbations development at the meanders of the different parts of Gulf Stream using the calculation of the increment of experimental curves for neutral stability. The evaluation results provide a basis for the development of realistic approaches to understanding the processes of generation and evolution of synoptic vortices in the meanders of intense oceanic jet currents.