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| Titel |
Gravity wave exclusion circles in background flows modulated by the semidiurnal tide |
| VerfasserIn |
L. Zhong, A. H. Manson, L. J. Sonmor, C. E. Meek |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 14, no. 5 ; Nr. 14, no. 5, S.557-565 |
| Datensatznummer |
250012294
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| Publikation (Nr.) |
 copernicus.org/angeo-14-557-1996.pdf |
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| Zusammenfassung |
| In this short paper the exclusion circles and
vertical phase locities for gravity waves launched from the ground into a
time-varying wind are studied using a ray-tracing technique. It is shown that
waves with initial observed phase speeds that should place them within the local
temporally varying exclusion circle, are often Doppler shifted outside of the
circle. This, and the finite lifetime of some critical levels, allow waves to
survive the critical layer and reach higher altitudes. Also, for slower
phase-speed waves, the temporally varying wind can shift the observed frequency
to negative values, so that the observed phase motions will be opposite (i.e.
horizontally reversed and vertically upward), even though the energy still
propagates upward. This effect can also cause the phase velocity to move inside
the local exclusion circle. Due to the directional filtering of wave sources by
the stratospheric wind, the percentage of such reverse-propagating waves will
change systematically with local time and height in our simplified but realistic
model. These results are related to ground-based systems, optical and radar,
which sample the wind field and gravity waves in the middle atmosphere. |
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