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

A recent study investigated the interaction of a self-propagating barotropic cyclonic eddy with a right vertical cylinder and determined the conditions for an eddy to bifurcate into two eddies. In the present study we performed two series of idealized laboratory experiments. The first series investigated the importance of the geometry of the obstacle, in particular its height, the slope of the side walls and the geometry of the horizontal cross sectional area. As in the previous study, after a self-propagating cyclonic eddy came in contact with the obstacle, fluid peeled off the outer edge of the vortex and a so called "streamer" went around the cylinder with a counterclockwise velocity. Under the right conditions, this fluid formed a new cyclonic vortex in the wake of the cylinder, causing bifurcation of the original vortex into two vortices. The present results suggest that bifurcation occurs only when the obstacle height is more than 0.85% of the eddy height and that fairly steep sloping walls do not influence the bifurcation mechanism. In addition, an elliptical horizontal cross section of the obstacle brought into light that an important parameter for the bifurcation to occur is the length the "streamer" has to travel around the obstacle and not the dimension of the obstacle in the direction orthogonal to the flow. The second series of experiments investigated the importance of two obstacles to the bifurcation of the self-propagating cyclonic eddy. Multiple eddies were generated by the interaction of a single cyclonic eddy with two right vertical cylinders. The exact number of eddies depends on the ratio of the obstacle separation to the eddy size and the geometry of the encounter. Furthermore, we observed the formation of an eddy of opposite sign, anticyclonic, at the downstream side of the gap between the two obstacles. This last observation in the laboratory is in agreement with recent observations of North Brazil Current Rings, suggesting that these very idealized laboratory experiments may bring some insights to the fate of mesoscale vortices in the Ocean.