Influence of Islands and Their 3-D Geometry on the Bifurcation of Eddies

Abstract: We investigated the interaction between a self-propagating barotropic cyclonic eddy with an obstacle and determined the conditions for an eddy to bifurcate into two eddies. A series of idealized laboratory experiments were carried out in a glass tank mounted concentrically on a 1 m diameter rotating turntable. As in a previous study, after a self-propagating cyclonic eddy came into contact with the obstacle, fluid peeled off the outer edge of the vortex and a so-called “streamer ” went around the cylinder in a counterclockwise direction. Under certain conditions, this fluid formed a new cyclonic vortex in the wake of the cylinder, causing bifurcation of the original vortex into two vortices. In the present study we performed three sets of idealized laboratory experiments. The goal of the first set was to investigate the importance of the slope of the side walls of the obstacle, the second set was performed to investigate the influence of the horizontal cross sectional area and the third set to investigate the importance of the height of the obstacle. All the experiments were carried out varying the geometry of the encounter, represented by the ratios Y/R and D/d, where Y is the distance between the center of the vortex and an axis passing through the center of the obstacle, R is half of the obstacle length orthogonal to the direction of propagation of the vortex, R2D = and d is the diameter of the incident vortex. The velocity and vorticity fields of the fluid, together with its trajectories, were obtained using the image analysis system Particle Tracking Velocimetry. The agreement between laboratory experiments and the observation of a “Meddy ” bifurcating after collision with the Irving Seamount in the Canary Basin suggests that these idealized laboratory experiments may yield new insights into the fate of mesoscale vortices in the ocean.