A model of a Mediterranean salt lens in external shear

Abstract

Abstract : A pair of models representing the interaction of a continuously stratified f-plane quasigeostrophic lens with an external shear flow are examined. The first models the eddy as a pair of quasigeostrophic 'point potential vortices' in uniform external shear; in the second the lens is represented by an isolated three dimensional patch with potential vorticity linear in z, which is embedded in a uniform shear. Analytical solutions are found representing a baroclinic lens with a trapped fluid core, which may propagate in the presence of external shear. An algorithm which is a generalization of the contour dynamics technique to stratified quasigeostrophic flows is used to extend these results into the nonlinear domain, allowing a determination of the range of conditions in which steadily translating solutions may be found. The stability of the solutions is examined numerically, and it is found that the solutions are stable if neither the external shear nor the core baroclinicity are too large. As a test of the model, new results from a recent SOFAR float experiment are presented. The data show that the cores of two different Mediterranean Salt lenses are tilted in agreement with the model solutions, presumably as a result of interactions with external flows. Quasigeostrophic vortex dynamics, Mediterranean salt lenses, Contour dynamics.