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.
Highlights
Due to the development of the general atmosphere and ocean circulation theory the particular attention is paid to the studies of the impact of both baroclinic and barotropic processes caused by vertical and horizontal rate shifts, on the development of the instability of largescale oceanic currents [1, 2]
We considered the problem of specifying the mechanism of the formation of rings due to the baroclinic instability of oceanic jet currents, the development of which is possible only in the rotating liquid stratified by density [6]
Jet currents belong to the class of motions in geological environments where horizontal shifts can have a significant impact on the formation of the barotropic instability of hydrodynamic processes in the ocean
Summary
Due to the development of the general atmosphere and ocean circulation theory the particular attention is paid to the studies of the impact of both baroclinic and barotropic processes caused by (respectively) vertical and horizontal rate shifts, on the development of the instability of largescale oceanic currents [1, 2]. The shift instability occurring during the horizontal rate steps may lead to the formation of vortices, the radius of which is typically lesser than Rossby radius of deformation [7] These vortices are observed on the outer periphery of Gulf Stream jet. Instability of the Oceanic Jet Currents processes is the problem of the stability of the system of two opposed jet currents in the rotating layer of shallow water and its solution based on the experimental research of jet currents with horizontal rate shift in the laboratory model, where the barothropic instability is presented in its pure form. In this work we consider the impact of the barotropic effects on the meandering of the oceanic jet currents and ring formation based on the laboratory experiments with differentially rotating shallow liquid
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