ANTICYCLONIC EDDIES LENSES FORMATION ABOVE A SLOPE BOTTOM IN A TWO-LAYER ROTATING FLUID UNDER THE ACTION OF THE TOPOGRAPHIC BETA-EFFECT

Abstract

One of the most striking hydrophysical structure in the ocean is intrapycnocline eddies lenses, or intrathermocline eddies (Filyushkin and Kozhelupova, 2020). They form in the region of intermediate-density water outflow from marginal seas into the World Ocean and have anticyclonic vorticity. They often form near canyons through which intermediate-density water flowing along the bottom of the continental slope, sink into the thickness of ocean waters at a horizon of equal density. In this work, laboratory experiments were conducted on the formation of eddies lenses in a homogeneous and two-layer stratified fluid in a cylindrical tank located on a rotating platform. An inscribed cone, apex upward, is inserted into the tank, forming an axisymmetric sloping bottom. The eddy flow is generated by a local vertical source of constant water flow, located above the cone at a distance of half the tank radius. In the case of a homogeneous fluid, water of the same density flowed from the tank; in the case of a two-layer fluid, water of intermediate density flowed directly into the region of the layer interface. In virtually all experiments, a self-oscillating mechanism for the formation of anticyclonic eddies lenses was observed, which drifted in the anticyclonic direction under the influence of the topographic beta effect (Zatsepin and Didkovsky, 1996). The eddy flow regimes were investigated over a determined range of variation in the experimental dimensionless parameters. A significant influence of the source water density value on the implementation of the self-oscillatory mechanism of eddies lens formation was found. If the density is close to the density of the water in the lower layer adjacent to the sloping bottom, this mechanism functions almost as efficiently as in a homogeneous surrounding fluid. If the density of the source water is close to the density of the water in the upper layer, the influence of the topographic beta effect weakens. Consequently, it can be assumed that the formation of intrathermocline eddies lenses due to the self-oscillatory mechanism in the World Ocean occurs most effectively if the separation of intermediate-density waters from the bottom slope occurs in the lower, and not in the upper region of the ocean pycnocline.