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| Titel |
Stochastic resonance in a nonlinear model of a rotating, stratified shear flow, with a simple stochastic inertia-gravity wave parameterization |
| VerfasserIn |
P. D. Williams, T. W. N. Haine, P. L. Read |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1023-5809
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| Digitales Dokument |
URL |
| Erschienen |
In: Nonlinear Processes in Geophysics ; 11, no. 1 ; Nr. 11, no. 1 (2004-02-25), S.127-135 |
| Datensatznummer |
250009029
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| Publikation (Nr.) |
 copernicus.org/npg-11-127-2004.pdf |
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| Zusammenfassung |
| We report on a numerical study of the impact of short, fast inertia-gravity waves
on the large-scale, slowly-evolving flow with which they co-exist. A nonlinear
quasi-geostrophic numerical model of a stratified shear flow is used to simulate,
at reasonably high resolution, the evolution of a large-scale mode which grows
due to baroclinic instability and equilibrates at finite amplitude. Ageostrophic
inertia-gravity modes are filtered out of the model by construction, but their
effects on the balanced flow are incorporated using a simple stochastic
parameterization of the potential vorticity anomalies which they induce. The
model simulates a rotating, two-layer annulus laboratory experiment, in which
we recently observed systematic inertia-gravity wave generation by an evolving,
large-scale flow. We find that the impact of the small-amplitude stochastic contribution to the
potential vorticity tendency, on the model balanced flow, is generally small, as
expected. In certain circumstances, however, the parameterized fast waves can
exert a dominant influence. In a flow which is baroclinically-unstable to a
range of zonal wavenumbers, and in which there is a close match between the growth
rates of the multiple modes, the stochastic waves can strongly affect wavenumber
selection. This is illustrated by a flow in which the parameterized fast modes
dramatically re-partition the probability-density function for equilibrated
large-scale zonal wavenumber. In a second case study, the stochastic perturbations
are shown to force spontaneous wavenumber transitions in the large-scale flow,
which do not occur in their absence. These phenomena are due to a stochastic
resonance effect. They add to the evidence that deterministic parameterizations in
general circulation models, of subgrid-scale processes such as gravity wave drag,
cannot always adequately capture the full details of the nonlinear interaction. |
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