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| Titel |
Properties of internal planetary-scale inertio gravity waves in the mesosphere |
| VerfasserIn |
H. G. Mayr, J. G. Mengel, E. R. Talaat, H. S. Porter, K. L. Chan |
| 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 ; 22, no. 10 ; Nr. 22, no. 10 (2004-11-03), S.3421-3435 |
| Datensatznummer |
250015021
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| Publikation (Nr.) |
 copernicus.org/angeo-22-3421-2004.pdf |
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| Zusammenfassung |
| At high latitudes in the upper mesosphere, horizontal wind
oscillations have been observed with periods around 10h. Waves with
such a period are generated in our Numerical Spectral Model (NSM), and they
are identified as planetary-scale inertio gravity waves (IGW). These IGWs
have periods between 9 and 11h and appear above 60km in the zonal mean
(m=0), as well as in m=1 to 4, propagating eastward and westward. Under
the influence of the Coriolis force, the amplitudes of the waves propagating
westward are larger at high latitudes than those propagating eastward. The
waves grow in magnitude at least up to about 100km and have vertical
wavelengths around 25km. Applying a running window of 15 days for spectral
analysis, the amplitudes in the wind field are typically between 10 and 20m/s
and can reach 30m/s in the westward propagating component for m=1 at
the poles. In the temperature perturbations, the wave amplitudes above 100km
are typically 5K and as large as 10K for m=0 at the poles. The IGWs
are intermittent but reveal systematic seasonal variations, with the largest
amplitudes occurring generally in late winter and spring. Numerical
experiments show that such waves are also generated without excitation of
the migrating tides. The amplitudes and periods then are similar, indicating
that the tides are not essential to generate the waves. However, the
seasonal variations without tides are significantly different, which leads
to the conclusion that non linear interactions between the semidiurnal tide
and planetary waves must contribute to the excitation of the IGWs. Directly
or indirectly through the planetary waves, the IGWs are apparently excited
by the instabilities that arise in the zonal mean circulation. When the
solar heating is turned off for m=0, both the PWs and IGWs essentially
disappear. That the IGWs and PWs have common roots in their excitation
mechanism is also indicated by the striking similarity of their seasonal
variations in the lower mesosphere. Compared to the PWs, however, the
planetary-scale IGWs propagate zonally with much larger phase speeds. In
contrast to the PWs, the IGWs thus are not affected much by interactions
with the background zonal winds whose seasonal variations drastically change
with altitude in the mesosphere. Since the IGWs can propagate through the
mesosphere without much interaction, except for viscous dissipation, one
should then expect that they reach the thermosphere above with significant
and measurable amplitudes. |
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