Item – Thèses Canada

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Numéro d'OCLC
1032895793
Lien(s) vers le texte intégral
Exemplaire de BAC
Auteur
Gauthier, Pierre.
Titre
Dveloppement de tourbillons baroclines marginalement instables.
Diplôme
Thèse (Doctor of Philosophy)--McGill University, 1988.
Éditeur
Montréal : McGill University, 1988.
Description
1 online resource
Notes
Comprend des références bibliographiques.
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Résumé
In the vicinity of the point of minimum critical shear of a quasi-geostrophic two-level model on the $ beta$-plane, the weakly nonlinear dynamics of developing baroclinic vortices can be described in terms of a nonlinear critical layer problem which, in the inviscid case, can be solved analytically. When the supercritical shear $ delta$ is such that 0 $<$ $ delta$ $ ll$ 1 and the initial conditions are sufficiently small, finite amplitude equilibration occurs even though the potential vorticity field in the bottom layer Q(X,Y,t) remains transient, the potential enstrophy being transferred to smaller and smaller scales. It is shown that the inviscid equilibrium amplitude of the unstable wave is larger by a factor of $ surd$2 than the one found by Pedlosky (1982-b) in the limit of small dissipation. This indicates that the limits t $ to$ $ infty$ and r $ to$ 0 are not interchangeable. Inviscid equilibration occurs when the mixing in the lowest layer results in the streamwise homogenization of the coarse-grained average (Q) of the potential vorticity which means that (Q) $ to$ f($ psi$), $ psi$ being the streamfunction. When $ delta$ and the initial conditions are equally important, depending on the nature of the latter, periodic solutions and finite equilibration are both possible. An example is given of a periodic case when $ delta$ = 0. The potential vorticity field then reversibly wraps and un-wraps around the streamlines and mixing does not occur. Finally, these exact solutions are used to judge the reliability of numerical results obtained from truncated spectral models. For cases where finite equilibration occurs, the resolution of a truncated model is only adequate for a finite period of time while for periodic cases, a model with sufficient resolution can represent correctly the exact solution for any length of time.
Autre lien(s)
digitool.library.mcgill.ca
Sujet
Physics, Atmospheric Science.