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  4. Stability Criterion for the Centrifugal Instability of Surface Intensified Anticyclones
 
research article

Stability Criterion for the Centrifugal Instability of Surface Intensified Anticyclones

Yim, Eunok  
•
Stegner, Alexandre
•
Billant, Paul
2019
Journal of Physical Oceanography

We investigate the linear stability of intense baroclinic anticyclones, with a particular focus on the centrifugal (inertial) instability. Various vertical and radial velocity profiles are studied. The vertical profiles are such that the velocity is maximum at the surface. These profiles correspond to oceanic eddies such as submesoscale mixed-layer eddies or intense mesoscale eddies in the upper thermocline. The results show that the main characteristics of the centrifugal instability (growth rate, vertical wavelength) depend weakly on the baroclinic structure of the anticyclone. The dominant azimuthal wavenumber is for small Burger number (Bu) and for higher Bu, where Bu is the square root of the ratio of the deformation radius over the characteristic eddy radius where the velocity is maximum. The marginal stability limits of the centrifugal instability for the different velocity profiles collapse approximately on a single curve in the parameter space (Ro, Bu), where is the Rossby number, with being the maximum velocity. By means of an asymptotic analysis for short vertical wavelength, an explicit prediction for the marginal stability limit is derived for a wide range of velocity profiles. We then suggest to use, for most of oceanic anticyclones, the instability criterion valid for a Gaussian eddy: where is the Ekman number, H is the eddy depth, and ν is the turbulent viscosity at the ocean surface. Some baroclinic anticyclones can remain stable even if they have a core region of negative absolute vorticity provided that they are small enough. This formula explains the few observations of intense anticyclonic eddies having a negative core vorticity around .

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Type
research article
DOI
10.1175/JPO-D-18-0088.1
Author(s)
Yim, Eunok  
Stegner, Alexandre
Billant, Paul
Date Issued

2019

Published in
Journal of Physical Oceanography
Volume

49

Issue

3

Start page

827

End page

849

Subjects

Baroclinic flows

•

Instability

•

Stability

Editorial or Peer reviewed

REVIEWED

Written at

OTHER

EPFL units
HEAD  
Available on Infoscience
June 7, 2024
Use this identifier to reference this record
https://infoscience.epfl.ch/handle/20.500.14299/208473
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