Topographic Stabilization of Ocean Rings

Abstract

AbstractCoherent large‐scale vortices in the open ocean can retain their structure and properties for periods as long as several years. However, the patterns of potential vorticity in such vortices suggest that they are baroclinically unstable and therefore should rapidly disintegrate. This study proposes a plausible explanation of the longevity of large‐scale ocean rings based on bottom roughness, which restricts flow in the lower layer and thereby stabilizes the eddy. We perform a series of simulations in which topography is represented by the observationally derived Goff‐Jordan spectrum. We demonstrate that topography stabilizes coherent vortices and dramatically prolongs their lifespan. In contrast, the same vortices in the flat‐bottom model exhibit strong instability and fragmentation on the timescale of weeks. A critical depth variance exists that allows vortices to remain stable and circularly symmetric indefinitely. Our investigation underscores the essential role played by topography in the dynamics of large‐ and meso‐scale flows.