On the stability of oceanic vortices: A solution to the problem?

This paper attempts to resolve the long-standing contradiction between the observed longevity of oceanic vortices and their theoretical instability. Using the model of quasigeostrophic, two-layer ocean, we show that a vortex in the upper layer can be stabilised by a circulation in the lower layer, such that the potential vorticity (PV) there is uniform. It is also argued that the assumption of uniform PV in the 'passive' layer corresponds to the fact that most oceanic vortices are shed by frontal currents and are alien to the well-mixed water masses around them.