Long-Term Evolution of Elongated Warm Eddies

Abstract

The purpose of this research is to investigate the evolution of elongated warm eddies. A shallow-water, reduced-gravity, primitive equation model is used to perform a multicase numerical experiment, which includes vortices of very different eccentricities and strengths. The above is partly motivated by the increased number of oceanic observations, performed in recent years, that show the wide variety of warm eddies. Under the assumption that an eddy can be approximately described as a solid-body rotating elliptical vortex, the evolution is followed using a least-squares fitting procedure. Results indicate that the majority of these eddies evolve toward less eccentric states, a process called axisymmetrization. A few of the most elongated eddies break up, and some of the less eccentric ones remain unchanged. Axisymmetrization seems to be triggered by instability and, in the space of the parameters that describe the elliptical vortex, the trajectories followed in each of the cases fairly approximate contours of the conserved quantity q0V1/2, where q0 is the potential vorticity at the center of the elliptical vortex and V its total volume.