The Propagation of Submesoscale Coherent Vortices

Abstract

A combined analytical and numerical examination of submesoscale coherent vortex (SCV) dynamics and propagation is conducted. This study is prompted by observations of the movement relative to their surroundings of one class of SCVs, that is, Meddies. An asymptotic analysis is performed to study the mechanics governing SCV propagation. It is found that the large-scale flow plays a dominant role in determining the trajectory of SCVs and that the ? effect and form drag of neighboring layers are weaker effects. As a result, SCVs propagate at a speed that is a density-weighted average of the flow in the surrounding layers. Meddies may thus move relative to the surrounding water, which is in accordance with observations. This theory extends previous studies on eddy propagation by considering more general situations. For example, a lenslike eddy embedded in a nonzonal, vertically and horizontally sheared flow is studied. A significant difference between this study and most previous related work is that the submesoscale nature of SCVs is exploited. It is this nature that leads to our conclusions about SCV drift. The theory is tested both by solving the asymptotic equations and through experiments with a primitive equation model. Agreement is found between the results of our numerical experiments and the analytical predictions, thus suggesting that the asymptotic analysis has captured the leading order behavior of SCV propagation.