Decay of monopolar vortices in a stratified fluid

The decay of monopolar vortices in a stratified fluid has been investigated experimentally, and the observations have been compared with an analytical decay model that accounts for both the increasing vertical thickness and the radial expansion of these pancake-like structures. The monopolar vortices were generated by two different forcing techniques, and the corresponding horizontal velocity field was measured by tracking passive tracer particles. It was found that the monopolar vortices are characterized by a core of single-signed vorticity and a ring of oppositely signed vorticity, and that their net circulation is zero. The observations are in good agreement with the theoretical model, which provides a better description of the vortex evolution than the diffusion models presented in earlier studies.