Linear baroclinic and parametric instabilities of boundary currents
| Autor: | Xavier Carton, Francis J. Poulin, Marc Pavec |
|---|---|
| Přispěvatelé: | Laboratoire de physique des océans (LPO), Institut de Recherche pour le Développement (IRD)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS), Department of Applied Mathematics [Waterloo], University of Waterloo [Waterloo], Actimar, ACTIMAR |
| Jazyk: | angličtina |
| Rok vydání: | 2011 |
| Předmět: |
Physics
010504 meteorology & atmospheric sciences Meteorology Baroclinity Computational Mechanics Rossby wave Astronomy and Astrophysics Mechanics 01 natural sciences Physics::Geophysics 010305 fluids & plasmas Boundary current Physics::Fluid Dynamics Wavelength Geophysics Amplitude Geochemistry and Petrology Mechanics of Materials Potential vorticity Barotropic fluid 0103 physical sciences Parametric oscillator Physics::Atmospheric and Oceanic Physics [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography 0105 earth and related environmental sciences |
| Zdroj: | Geophysical and Astrophysical Fluid Dynamics Geophysical and Astrophysical Fluid Dynamics, Taylor & Francis, 2011, 105 (4-5), pp.453-477. ⟨10.1080/03091929.2010.490556⟩ |
| ISSN: | 0309-1929 1029-0419 |
| Popis: | International audience; The linear baroclinic and parametric instabilities of boundary currents with piecewise-constant potential vorticity are studied in a two-layer quasi-geostrophic model. The growth rates of both the exponential modes and of the optimal perturbations are calculated for the baroclinic instability of steady coastal currents. We show that the growth rates of the exponential modes are maximal for a vertically symmetric flow. Furthermore, the vertical asymmetries induced by different layer thicknesses, the presence of a barotropic potential vorticity or bottom topography, all act to dampen the growth rates and favor growth at shorter wavelengths. It is shown that this behavior can be predicted from the conditions for vertical resonance of Rossby waves on the two potential vorticity fronts. Also, the baroclinic instability of the optimal perturbations has larger growth rates at shorter wavelengths and shorter time scales. As well, the presence of a sloping bottom of moderate amplitude favors the growth of these optimal perturbations. Finally, we compute the growth rates of parametric instability of oscillatory coastal flows. We show that subharmonic resonance is the most unstable mode of growth. In addition, a second region of parametric instability is found (for the first time) away from marginality of exponential-mode baroclinic instability. It is shown that the functional dependency of the growth rates of parametric instability, for optimal excitation, are similar to that of the optimal perturbations of baroclinic instability. To explain this a mechanism for parametric instability, involving the rapid growth of short-wave optimal perturbations, is proposed. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
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