PRELIMINARY RESULTS OF LABORATORY INVESTIGATIONS OF THE EVOLUTION OF NON-FRONTAL EDDIES IN A TWO-LAYERED ROTATING FLUID

Abstract

In this work, by means of laboratory modeling, the patterns of evolution (baroclinic instability and/or viscous degeneration) of mesoscale non-frontal baroclinic eddies, or open ocean eddies (without a core with the water of different density) were revealed. The experiment was provided in a two-layer salinity-stratified aquatic environment in a cylindrical tank located on a rotating platform. Using the original application of the “cylinder method”, single axisymmetric cyclonic and anticyclonic eddies were produced in the upper layer, and their evolution was traced over 100 or more platform rotation periods (laboratory days). It has been established that the vortices lose their stability if the value of the defining parameter representing the ratio of the Burger and Froude numbers is less than the critical one. In this case, eddies either fall apart into two or more secondary vortices (strong instability) or acquire an elongated shape (weak instability). The slope of the bottom and its roughness increase the stability of eddies. For values of the determining parameter greater than the critical one, the vortices are stable and gradually degenerate due to viscous friction. In the case of a large difference in salinity (density) between the layers, the bottom roughness does not have a significant effect on the rate of upper layer eddy damping, which, apparently, is determined by the friction in this layer. A parametrization is proposed that describes the exponential law of eddy decay, which is tested on the example of the Black Sea mesoscale eddy.