DYNAMICS OF A NONLINEAR DIPOLE VORTEX

A localized stationary dipole solution to the Euler equations with a r elationship between the vorticity and streamfunction given as omega=-p si+psi(3) is presented. By numerical integration of the Euler equation s this dipole is shown to be unstable. However, the initially unstable dipole reorganizes itself into a new nonlinear dipole, which is found to be stable. This new structure has a functional relationship given as omega=alpha psi+beta psi(3)-gamma psi(5). Such dipoles are stable t o head-on collisions and they are capable of creating tripolar structu res when colliding off axis. The effects of increasing Newtonian visco sity on the nonlinear dipole is studied revealing that even though the nonlinearity is weakening, the dipole does not relax towards a Lamb d ipole. (C) 1995 American Institute of Physics.