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Fluids 2017, 2(4), 57; doi:10.3390/fluids2040057

The Interaction of Two Surface Vortices Near a Topographic Slope in a Stratified Ocean

1
École Normale Supérieure de Lyon, 69007 Lyon, France
2
Laboratoire d’Océanographie Physique et Spatiale, Institut Universitaire Européen de la Mer, Université de Bretagne Occidentale, 29200 Brest, France
3
Vortex Dynamics Group, Mathematical Institute, University of St Andrews, Scotland KY16 9SS, UK
*
Author to whom correspondence should be addressed.
Received: 21 July 2017 / Revised: 10 October 2017 / Accepted: 17 October 2017 / Published: 25 October 2017
(This article belongs to the Collection Geophysical Fluid Dynamics)

Abstract

We study the influence of bottom topography on the interaction of two identical vortices in a two-layer, quasi-geostrophic model. The two vortices have piecewise-uniform potential vorticity and are lying in the upper layer of the model. The topography is a smooth bottom slope. For two cyclones, topography modifies the merger critical distance and the merger efficiency: the topographic wave and vortices can advect the two cyclones along the shelf when they are initially far from it or towards the shelf when they are initially closer to it. They can also advect the two cyclones towards each other and thus favour merger. The cyclones deform, and the potential vorticity field undergoes filamentation. Regimes of partial vortex merger or of vortex splitting are then observed. The interaction of the vorticity poles in the two layers are analysed to explain the evolution of the two upper layer cyclones. For taller topography, two new regimes appear: vortex drift and splitting; and filamentation and asymmetric merger. They are due to the hetonic coupling of lower layer vorticity with the upper layer vortices (a heton is a baroclinic vortex dipole, carrying heat and momentum and propagating horizontally in the fluid), or to the strong shear that the former exerts on the latter. The interaction of two anticyclones shows regimes of co-rotation or merger, but specifically, it leads to the drift of the two vortices away from the slope, via a hetonic coupling with oppositely-signed vorticity in the lower layer. This vorticity originates in the breaking of the topographic wave. The analysis of passive tracer evolution confirms the inshore or offshore drift of the fluid, the formation of tracer fronts along filaments and its stirring in regions of vortex merger. The trajectories of particles indicate how the fluid initially in the vortices is finally partitioned. View Full-Text
Keywords: vortex interaction; topography; quasi-geostrophic model vortex interaction; topography; quasi-geostrophic model
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

de Marez, C.; Carton, X.; Morvan, M.; Reinaud, J.N. The Interaction of Two Surface Vortices Near a Topographic Slope in a Stratified Ocean. Fluids 2017, 2, 57.

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