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| Titel |
Centrifugal, barotropic and baroclinic instabilities of isolated ageostrophic anticyclones in the two-layer rotating shallow-water model and their nonlinear saturation |
| VerfasserIn |
Noé Lahaye, Vladimir Zeitlin |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250092959
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| Publikation (Nr.) |
 EGU/EGU2014-7324.pdf |
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| Zusammenfassung |
| Mesoscale and submesoscales eddies are ubiquitous in the ocean, and much effort is
dedicated to the analysis of such structures, especially in what concerns their stability. While
quasi-geostrophic (barotropic and baroclinic) instabilities have been well documented for the
last decades, we have fully realized relatively recently that other ageostrophic instabilities –
in particular the centrifugal instability – play a role in the submesoscale dynamics. The
importance of such a mechanism, besides being responsible for coherent vortex structure
breakdown, resides in the fact that it produces overturning vertical motions that enhance
strong mixing and energy dissipation. The impact of the vertical structure of the flow
(vertical shear and stratification) upon the centrifugal instablity is still an issue to be
clarified.
In this paper, we study the instabilities of the isolated anticyclonic vortices in the 2-layer
rotating shallow water model at Rossby numbers up to 2, with the main goal to understand
the interplay between the classical centrifugal instability and other possible ageostrophic
instabilities.
We find that different types of instabilities with low azimuthal wavenumbers exist, and
may compete. In a wide range of parameters an asymmetric version of the standard
centrifugal instability has larger growth rate than this latter. The dependence of the
instabilities on the parameters of the flow: Rossby and Burger numbers, vertical shear, and
the ratios of the layers’ thicknesses and densities is investigated. The zones of dominance of
each instability are determined in the parameter space. It is shown that density step tends to
inhibit the centrifugal instabilities and may thus play a key role on the issue of the
destabilization process in parameters regimes where they compete with the barotropic
instability.
Nonlinear saturation of these instabilities is then studied with the help of a high-resolution
finite-volume numerical scheme, by using the unstable modes identified from the linear
stability analysis as initial conditions. Differences in nonlinear development of the competing
centrifugal and ageostrophic barotropic instabilities are evidenced. |
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