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| Titel |
Spectral evolution of two-layer weak geostrophic turbulence. Part I: Typical scenarios |
| VerfasserIn |
T. Soomere  |
| 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 ; 3, no. 3 ; Nr. 3, no. 3, S.166-195 |
| Datensatznummer |
250001021
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| Publikation (Nr.) |
 copernicus.org/npg-3-166-1996.pdf |
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| Zusammenfassung |
Long-time evolution of
large-scale geophysical
flows is considered in a β-plane approximation.
Motions in an
infinite 2-layer model ocean are treated as a system of
weakly
nonlinear Rossby waves (weak geostrophic turbulence).
The
evolution of the energy spectrum of the barotropic
and the
baroclinic modes is investigated on the basis of
numerical
experiments with the kinetic equation for
baroclinic Rossby
waves.
The basic features of free (nonforced inviscid)
spectral evolution of baroclinic flows are similar to those
of the
barotropic motions. A portion of the energy is
transferred to
a sharp spectral peak while the rest of it is
isotropically
distributed. The peak corresponds to an intensive
nearly zonal
barotropic flow. Typically, this well-defined
barotropic zonal
anisotropy inhibits the reinforcement of
its baroclinic
analogy. For a certain set of initial
conditions (in
particular, if the barotropic zonal flow is not
present
initially), a zonal anisotropy of both modes is
generated.
The interplay between the multimodal nearly zonal
flow
components leads to the excitation of large-scale
(several
times exceeding the scale of the initial state),
mostly meridional, baroclinic motions at the expense
of the
barotropic nearly zonal flow. The underlying
mechanism is
explained on the level of elementary mixed-triad
interaction.
The whole wave field retains its essentially
baroclinic as
well as spectrally broad nature. It evidently
tends towards a
thermodynamically equilibrated final state, consisting
of the
superposition of a (usually barotropic, but
occasionally multimodal) zonal flow and a wave system with a
Raleigh-Jeans
spectrum. This evolution takes place as a
multi-staged process, with fast convergence of the modal spectra to
a local equilibrium followed by a more gradual adjustment of
the energy balance between the modes. |
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