Deformation and splitting of baroclinic eddies encountering a tall seamount

Abstract

The transformation of baroclinic eddies encountering a tall seamount is explored using a three-layer primitive equation model on the β-plane. The topography is finite in that the seamount penetrates the isopycnal layer in which the eddy resides, but does not span the entire fluid depth. In our numerical simulations, the eddies are represented by potential vorticity anomalies in the upper and middle layers, and propagating towards the seamount due to the beta-effect. Circulations created near the topography, both by fluid removed from the seamount and by external fluid stranded over the seamount, play a key role in the drift, deformation, and erosion of the approaching eddies. When the radius of the seamount is small, the deviation of the eddy trajectory is well described by a simple kinematic model that does not take into account deformations of the vortex cores. For wider seamounts, such interactions may result in horizontal and/or vertical splitting of the vortex core, i.e., in increased occurrences of eddy destruction. In particular, an interesting mechanism is found, related to enhancement of topographic circulation by potential vorticity entrained from the vortex core in the middle layer, and resulting in strong deformations and splitting of the upper layer core. Numerical estimates of the transformed eddy structure indicate that topographic interactions provide powerful mechanisms for significantly influencing baroclinic eddy evolution. Our results are summarized in a specific nondimensional parameter space according to the eddy evolution.

Keywords:

• Mesoscale dynamics
• Vortex/Seamount encounter
• Ocean eddies
• Vortex splitting

Acknowledgements

G. Sutryrin acknowledges support from the NSF Division of Ocean Sciences and from CNRS; the hospitality during his visit at the “Laboratoire de Physique des Océans” (Université de Bretagne Occidentale-Brest-France) was greatly appreciated. X. Carton acknowledges support from the Université de Bretagne Occidentale, from CNRS (National Center for Scientific Research) and from the Brittany Region for the organization of the 2nd International Conference on high Reynolds number vortex interactions, at which this work was presented. S. Herbette also acknowledges support from the Université de Bretagne Occidentale. Finally, all authors thank the anonymous reviewers for their helpful suggestions.

Notes

^†A zonal drift speed could be defined by the integral relations of Mory (1985).