Underwater Ridge Impact on the Motion of Anticyclonic Eddies over a Sloping Bottom as a Result of the Topographic Beta-Effect: Laboratory Experiment

Purpose. The work is purposed at investigating the underwater ridge impact on the motion of anticyclonic eddies over a sloping bottom as result of the topographic beta-effect in the laboratory conditions. Methods and Results. The experiments are carried out in a cylindrical tank located on a rotating platform. A cone is placed into the tank so that its base coincides with the cylinder lower base. The cone height is less than the base radius. Before the start of each experiment, the tank is filled with fresh or salt water of certain salinity. The fluid layer height exceeds that of the cone in the tank. The anticyclonic eddies are generated using a local constant source of a blue-colored fresh water flow. The source is located directly below the water layer surface at a distance equal to a half of the tank's radius from its center. Having achieved the critical diameter, the generated eddies drift along the isobaths in the "western" direction ("north" is at the cone top in the tank center) due to the topographic beta-effect. The experiments were carried out over the cone with a smooth surface, and over the cone with a ridge on its side whose height was significantly smaller than that of the cone located on the path of the eddy drift. In the experimental runs with the ridge, the drift both of barotropic (fresh water in the tank) and baroclinic (salt water in the tank) eddies slowed down as compared to the eddy drift velocities in the absence of the ridge. After crossing the ridge, the orbital velocity of the eddies also decreased significantly. Conclusions. Field observations and numerical modeling of the Sevastopol anticyclonic eddy in the Black Sea moving over the continental slope along the isobaths in the southwestern direction showed that the eddy motion slowed down in the area of the underwater ridge formed by a local rise in the bottom relief between two canyons - the Danube and the Western Dnieper paleochannels. The results of the laboratory experiment have confirmed the data of field observations and numerical modeling on a slowdown of the Sevastopol eddy motion and a decrease in its orbital velocity while crossing the underwater ridge due to the topographic beta-effect.