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| Titel |
Characterization of ultra low frequency (ULF) pulsations and the investigation of their possible source |
| VerfasserIn |
S. H. Mthembu, S. B. Malinga, A. D. M. Walker, L. Magnus |
| 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 ; 27, no. 8 ; Nr. 27, no. 8 (2009-08-26), S.3287-3296 |
| Datensatznummer |
250016631
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| Publikation (Nr.) |
 copernicus.org/angeo-27-3287-2009.pdf |
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| Zusammenfassung |
| In this paper we present the results from the observation of ultra low
frequency (ULF) pulsations in the Doppler velocity data from SuperDARN HF
radar located at Goose Bay (61.94° N, 23.02° E, geomagnetic).
Fourier spectral techniques were used to determine the spectral content of
the data and the results show Pc 5 ULF pulsations (with a frequency range of
1 to 4 mHz) where the magnetic field lines were oscillating at discrete
frequencies of about 1.3 and 1.9 mHz. These pulsations are classified as
field lines resonance (FLR) since the 1.9 mHz component exhibited an
enhancement in amplitude with an associated phase change of approximately
180° across a resonance latitude of 71.3°. The spatial and
temporal structure of the ULF pulsations was examined by investigating their
instantaneous amplitude which was calculated as the amplitude of the
analytic signal. The results presented a full field of view which exhibit
pulsations activity simultaneously from all beams. This representation shows
that the peak amplitude of the 1.9 mHz component was observed over the
longitudinal range of 13°. The temporal structure of the pulsations was
investigated from the evolution of the 1.9 mHz component and the results
showed that the ULF pulsations had a duration of about 1 h. Wavelet
analysis was used to investigate solar wind as a probable source of the
observed ULF pulsations. The time delay compared well with the solar wind
travel time estimates and the results suggest a possible link between the
solar wind and the observed pulsations. The sudden change in dynamic
pressure also proved to be a possible source of the observed ULF pulsations. |
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