FINITE AREA BETA-PLANE DIPOLES

We study a class of vortex dipoles consisting of two patches of unifor m potential vorticity in an otherwise quiescent flow on a beta-plane. Steadily propagating solutions that are desingularised analogues of po int vortex dipoles are found and compared with the point vortex soluti ons. Like the point vortex dipoles, both rapidly and slowly propagatin g solutions exist. Numerical simulations show that the slow solutions are unstable and break up under the influence of weak external perturb ations. The fast solutions are more robust. The minimum dipole strengt h necessary for the existence of a steadily propagating solution is le ss than that found for point vortex dipoles.