Dynamics, stability, and evolutionary patterns of mesoscale intrathermocline vortices

Abstract

Mesoscale intrathermocline eddies play an important role in transferring heat, salinity, and momentum in large-scale flows, actively influencing the general circulation of the ocean. Nevertheless, the factors controlling the longevity and coherence of mesoscale eddies are much debated. One of the key questions is the relative significance of double diffusion and turbulence in the dispersion of mesoscale variability. Several observational studies have implicated the lateral intrusions, driven by double-diffusive mixing, in the ultimate disintegration of eddies. However, observational limitations precluded unambiguous quantification of the impact of interleaving on the basis of field measurements. To the best of our knowledge, this research presents the first intrusion-resolving numerical simulation of a mesoscale eddy. This study is focused on the dynamics of a Mediterranean eddy (meddy). Double diffusion and turbulence of various strengths are applied to both static and dynamic (rotating) eddies in order to isolate the effects and determine the dominant players. The prominent findings of this study are threefold: (1) Double diffusion is a key process in dissipating an eddy. (2) Lateral diffusivity values calculated from the numerical simulations fall within the range of observed values. (3) A static eddy dissipates in a very different manner from a dynamic eddy, which underscores inherent limitations of intrusion modeling in quiescent background states. Finally, it should be emphasized that while the key physical processes at play are illustrated here on a specific example of meddies, the broader implications of our findings are much more fundamental and far-reaching. It is our belief that this study provides a clue to one of the long-standing problems in physical oceanography, namely, the link between the basin-scale forcing of the ocean by air-sea fluxes and the dissipation of energy and thermal variance at the microscale.