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| Titel |
Gravity wave penetration into the thermosphere: sensitivity to solar cycle variations and mean winds |
| VerfasserIn |
D. C. Fritts, S. L. Vadas |
| 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 ; 26, no. 12 ; Nr. 26, no. 12 (2008-12-02), S.3841-3861 |
| Datensatznummer |
250016314
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| Publikation (Nr.) |
 copernicus.org/angeo-26-3841-2008.pdf |
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| Zusammenfassung |
| We previously considered various aspects of gravity wave penetration and
effects at mesospheric and thermospheric altitudes, including propagation,
viscous effects on wave structure, characteristics, and damping, local body
forcing, responses to solar cycle temperature variations, and filtering by
mean winds. Several of these efforts focused on gravity waves arising from
deep convection or in situ body forcing accompanying wave dissipation. Here
we generalize these results to a broad range of gravity wave phase speeds,
spatial scales, and intrinsic frequencies in order to address all of the
major gravity wave sources in the lower atmosphere potentially impacting the
thermosphere. We show how penetration altitudes depend on gravity wave phase
speed, horizontal and vertical wavelengths, and observed frequencies for a
range of thermospheric temperatures spanning realistic solar conditions and
winds spanning reasonable mean and tidal amplitudes. Our results emphasize
that independent of gravity wave source, thermospheric temperature, and
filtering conditions, those gravity waves that penetrate to the highest
altitudes have increasing vertical wavelengths and decreasing intrinsic
frequencies with increasing altitude. The spatial scales at the
highest altitudes at which gravity wave perturbations are observed are
inevitably horizontal wavelengths of ~150 to 1000 km and vertical
wavelengths of ~150 to 500 km or more, with the larger horizontal
scales only becoming important for the stronger Doppler-shifting conditions.
Observed and intrinsic periods are typically ~10 to 60 min and ~10 to
30 min, respectively, with the intrinsic periods shorter at the
highest altitudes because of preferential penetration of GWs that are
up-shifted in frequency by thermospheric winds. |
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