Laboratory experiments on mesoscale vortices colliding with a seamount

[1] Interaction between a vortex and a right vertical cylinder was investigated in the laboratory for both a self-propagating vortex and one advected by a background uniform flow. In the former case, experiments were carried out with a sloping bottom in order to simulate the beta plane. In the latter case the bottom was flat and a cylinder was towed, with a uniform speed, through a fluid otherwise at rest and into a stationary vortex. In both cases, after a cyclonic vortex came in contact with the cylinder, fluid peeled off the outer edge of the vortex and went around the cylinder with a counterclockwise velocity vs as predicted by the circulation equation. This fluid formed a new cyclonic vortex in the wake of the cylinder, and bifurcation of the original vortex into two vortices occurred provided 400 Re 1100, where the Reynolds number Re = v(s)L(max)/nu and L-max is the larger of the vortex or the cylinder diameter. This result is in agreement with previous studies of uniform flow past a cylinder in a rotating environment, and therefore we suggest that the new vortex in the wake of the cylinder was formed like those in the well-known Karman vortex street. Experiments have been carried out systematically by varying D/d, the ratio of the cylinder diameter to the vortex diameter and the geometry of the encounter. The results suggest that the presence of a background flow enhances the bifurcation mechanism. A good agreement between the laboratory experiments and the observation of a meddy bifurcating after collision with the Irving Seamount in the Canary Basin, suggests that the oceanic vortex-bifurcation process is similar to that observed in the laboratory experiments.