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Inertial instability of intense stratified anticyclones. Part 2. Laboratory experiments

Published online by Cambridge University Press:  06 September 2013

Ayah Lazar*
Affiliation:
Department of Geophysics and Planetary Science, Tel Aviv University, Tel Aviv, Tel Aviv 69978, Israel Laboratoire de Météorologie Dynamique, École Polytechnique, 91128 Palaiseau CEDEX, France
A. Stegner
Affiliation:
Laboratoire de Météorologie Dynamique, École Polytechnique, 91128 Palaiseau CEDEX, France UME, ENSTA Centre de l’Yvette, Chemin de la Hunière, 91761 Palaiseau CEDEX, France
R. Caldeira
Affiliation:
CIIMAR – Interdisciplinary Centre of Marine and Environmental Research, 289 Rua dos Bragas, 4050-123 Porto, Portugal
C. Dong
Affiliation:
Institute of Geophysics and Planetary Physics, University of California, 603 Charles E. Young Drive, East, Los Angeles, CA 90095-1567, USA
H. Didelle
Affiliation:
LEGI/Coriolis, 21 Avenue des Martyrs, 38000 Grenoble, France
S. Viboud
Affiliation:
LEGI/Coriolis, 21 Avenue des Martyrs, 38000 Grenoble, France
*
Email address for correspondence: ayahlazar@gmail.com

Abstract

Large-scale laboratory experiments were performed on the Coriolis rotating platform to study the stability of intense vortices in a thin stratified layer. A linear salt stratification was set in the upper layer on top of a thick barotropic layer, and a cylinder was towed in the upper layer to produce shallow cyclones and anticyclones of similar size and intensity. We focus our investigations on submesoscale eddies, where the radius is smaller than the baroclinic deformation radius. Towing speed, cylinder size and stratification were changed in order to cover a large range of the parameter space, staying in a relatively high horizontal Reynolds number ($Re= 2000{{\unicode{x2013}}}7000$). The Rayleigh criterion states that inertial instabilities should strongly destabilize intense anticyclonic eddies if the vorticity in the vortex core is negative enough ${\zeta }_{0} / f\lt - 1$, where ${\zeta }_{0} $ is the relative vorticity in the core of the vortex, and $f$ is the Coriolis parameter. However, we found that some anticyclones remain stable even for very intense negative vorticity values, up to ${\zeta }_{0} / f= - 3. 5$, when the Burger number is large enough. This is in agreement with the linear stability analysis performed in part 1 (J. Fluid Mech., vol. 732, 2013, pp. 457–484), which shows that the combined effect of a strong stratification and a moderate vertical dissipation may stabilize even very intense anticyclones, and the unstable eddies we found were located close to the marginal stability limit. Hence, these experimental results agree well with the simple stability diagram proposed in the Rossby, Burger and Ekman parameter space for inertial destabilization of viscous anticyclones within a shallow and stratified layer.

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Papers
Copyright
©2013 Cambridge University Press 

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Lazar et al. supplementary movie

The surface vorticity field, normalised by the Coriolis parameter, for experiment 10. This is the whole movie of the snapshots shown in figure 7.

Download Lazar et al. supplementary movie(Video)
Video 10.3 MB