DECAY OF MONOPOLAR VORTICES IN A STRATIFIED FLUID

The decay of monopolar vortices in a stratified fluid has been investi gated 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. T he monopolar vortices were generated by two different forcing techniqu es, and the corresponding horizontal velocity field was measured by tr acking passive tracer particles. It was found that the monopolar vorti ces 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, w hich provides a better description of the vortex evolution than the di ffusion models presented in earlier studies. (C) 1998 The Japan Societ y of Fluid Mechanics Incorporated and Elsevier Science B.V. All rights reserved.