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| Titel |
Interfacial and trapped waves in flows over mountains |
| VerfasserIn |
Johannes Sachsperger, Stefano Serafin, Vanda Grubišić |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250109951
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| Publikation (Nr.) |
 EGU/EGU2015-9905.pdf |
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| Zusammenfassung |
| The horizontal propagation of internal waves in stratified fluids is
often explored in the context of Scorer’s theory of wave trapping in a
two-layer atmosphere, where a discontinuity in the Scorer parameter -
with evanescent conditions in the upper layer - gives rise to trapped
lee waves. The frequency dispersion relationship (FDR) of these waves
suggests that their horizontal wavelength depends on the Scorer
parameters in both layers and on the depth of the lower layer.
Horizontal wave motion can also occur in form of interfacial waves along
a density discontinuity in the interior of a fluid, similar to surface
waves on a free water surface. The wavelength of interfacial waves is
defined by the height and strength of the discontinuity and by the
horizontal wind speed.
We modify Scorer’s wave trapping theory by applying a boundary condition
that accounts for a density jump between the two stratified layers. In
this case, wave resonance is possible along the density jump even if the
lower layer is neutrally stratified. Therefore, both interfacial waves
and trapped lee waves are supported. The resulting linear theory can be
applied for instance to boundary layer flows over complex terrain, where
part of the mountain wave energy can be trapped along the inversion that
caps the boundary layer.
We show that, under certain combinations of parameters, trapped lee
waves behave exactly as pure interfacial waves, i.e. they obey to
identical FDRs. Since trapped lee waves and interfacial waves have
transcendental FDRs that cannot be solved analytically, we also discuss
the implications of the shallow- and deep-water approximations on the
wavelength of the resonant mode. |
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