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| Titel |
Gain of balance and critical level absorption for inertio gravity waves |
| VerfasserIn |
François Lott, Christophe Millet, Jacques Vanneste |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250090677
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| Publikation (Nr.) |
 EGU/EGU2014-4931.pdf |
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| Zusammenfassung |
| The absorption of an inertio gravity wave (IGW) at critical levels is analyzed in the rotating
linear case, and for a constant vertically sheared flow. We give for the first time
an exact solution valid over the entire domain, and check its validity by deriving
from it the classical values of the transmission and reflection coefficients of the
wave |T| = exp( )
- Ï°J-(1+-ν2)–0.25- and |R| = 0, respectively. Here J is the
Richardson number and ν the ratio between the horizontal transverse and along shear
wavenumbers.
For large J, a WKB analysis permits to interpret this classical result in term of
tunneling. In this interpretation, the wave as it arrives to the lowest inertial critical
level becomes evanescent (there is a turning point very near the critical level), and
the transmitted signal is just the amplitude of this evanescent disturbance at the
upper inertial level where it becomes an IGW again. As this evanescent solution
is near a quasi-geostrophic solution between the inertial levels we see that it is
a gain of balance there that explain the exponential smallness of the transmitted
wave.
The exact and approximate solutions also permit to describe how the "valve"
effect, which amplify the disturbances with phase line tilted in the direction of the
isentropes, is only significant when the flow is inertially unstable (when J < 1). In
this case, a small incident asymmetric transverse wave can result in a very large
disturbance between the inertial levels, a result that establish a correspondence
between the absoptive properties of the shear layer and the criteria for flow stability. |
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