Generation and Separation of Mesoscale Eddies from Surface Ocean Fronts

This study is motivated by Arctic Ocean observations of sub-mixed layer eddies found at large distances from their assumed formation region of a surface ocean front. Eddy formation is explored through high-resolution numerical simulations of surface fronts, separating two mixed layers, with a range of configurations similar to those observed in the Arctic Ocean. This study finds that frontal instabilities lead to the development of self-propagating dipoles, which have the potential to propagate far from the front if interactions with other eddies are avoided. However, most dipoles are unbalanced, consisting of a dominating surface cyclone and a weaker anticyclone below, and thus propagate on curved trajectories with eventual recirculation back to the front. Their maximum separation distance from the front depends on the ratio of self-advecting velocities E; balanced dipoles that have E approximate to 1, and the ability to propagate far from the front. For dipoles generated numerically, this study estimates E using analytical solutions of a 21/2-layer quasigeostrophic model for Gaussian vortices. The distribution of the ratio E for these dipoles is found to be skewed toward higher values (i.e., cyclones are dominant in dipoles). Sensitivity experiments suggest that shallow fronts that separate mixed layers of approximately equal depths favor the development of balanced dipoles that can self-propagate over long distances.