Experiments on barotropic vortex-wall interaction on a topographic β plane

The problem of a barotropic cyclonic vortex, moving on a ß plane and interacting with a meridional vertical wall, is studied by means of laboratory experiments and a finite difference numerical model. In the laboratory, the vortex is produced in a rectangular rotating tank with a weakly sloping bottom. This socalled topographic ß plane simulates the latitudinal variations of the Coriolis parameter (ß effect). On this ß plane, the cyclonic vortex moves to the northwest and eventually interacts with the western wall. Two different results are found, depending on the initial strength and zonal position of the vortex. (1) For strong vortices, opposite-sign vorticity is created at the wall owing to the no-slip boundary condition, which leads, together with the cyclone, to the formation of a dipole structure that subsequently moves away from the wall in the northeastward direction. New wall interactions may occur when the original vortex recovers its northwestward motion. (2) In the case of weak vortices, the cyclone remains approximately at the same latitude for some time and later drifts slowly southward until it is dissipated by viscous effects. It is proposed that this behavior is a consequence of the vortex dispersion due to the ß effect.