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| Titel |
Wavelet analysis on transient behaviour of tidal amplitude fluctuations observed by meteor radar in the lower thermosphere above Bulgaria |
| VerfasserIn |
D. Pancheva, P. Mukhtarov |
| 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 ; 18, no. 3 ; Nr. 18, no. 3, S.316-331 |
| Datensatznummer |
250013934
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| Publikation (Nr.) |
 copernicus.org/angeo-18-316-2000.pdf |
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| Zusammenfassung |
On the basis of bispectral analysis applied
to the hourly data set of neutral wind measured by meteor radar in the MLT
region above Bulgaria it was demonstrated that nonlinear processes are
frequently and regularly acting in the mesopause region. They contribute
significantly to the short-term tidal variability and are apparently responsible
for the observed complicated behavior of the tidal characteristics. A Morlet
wavelet transform is proposed as a technique for studying nonstationary signals.
By simulated data it was revealed that the Morlet wavelet transform is
especially convenient for analyzing signals with: (1) a wide range of dominant
frequencies which are localized in different time intervals; (2) amplitude and
frequency modulated spectral components, and (3) singular, wave-like events,
observed in the neutral wind of the MLT region and connected mainly with
large-scale disturbances propagated from below. By applying a Morlet wavelet
transform to the hourly values of the amplitudes of diurnal and semidiurnal
tides the basic oscillations with periods of planetary waves (1.5-20 days), as
well as their development in time, are obtained. A cross-wavelet analysis is
used to clarify the relation between the tidal and mean neutral wind
variability. The results of bispectral analysis indicate which planetary waves
participated in the nonlinear coupling with the atmospheric tides, while the
results of cross-wavelet analysis outline their time intervals if these
interactions are local.
Key words: Meteorology and atmospheric dynamics (middle
atmosphere dynamics; waves and tides) - Radio science (nonlinear phenomena) |
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