MERGING OF BAROTROPIC SYMMETRICAL VORTICES - A CASE-STUDY FOR GULF-STREAM RINGS

We made numerical experiments to study the merging dynamics of axisymmetric barotropic ringlike vortices using a quasi-geostrophic model in a beta-plane. We want to explore the initial conditions and the physical parameters that cause the merging or that affect the merging rates of ringlike structures. The initial vortices have a [[realistic]] shape, i.e., they are taken to simulate closely the horizontal structure of Gulf Stream rings. In the first set of experiments we change the initial separation distance d between the two vortices: for bigger merging distances the process cannot occur. The initial distance affects the merging rates and it determines the development of the lateral arms and the behaviour of the <<near-field>> vortices. The latter form near the elongated arms of the merging vortices; sometimes the arms of the merged vortex become unstable and get detached from the central merged vorticity region to form dipolar structures with <<near-field>> vortices. A second set of numerical simulations is done by changing the numerical model parameters. The results show that the merging is a nonlinear process very sensitive to the value of the nonlinear parameter, alpha, and that the beta-effect does not alter appreciably the speed of merging but it affects the development of the arms.