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| Titel |
The role of upstream ULF waves in the generation of quasi-periodic ELF-VLF emissions |
| VerfasserIn |
K. Morrison, M. P. Freeman |
| 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 ; 13, no. 11 ; Nr. 13, no. 11, S.1127-1133 |
| Datensatznummer |
250012035
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| Publikation (Nr.) |
 copernicus.org/angeo-13-1127-1995.pdf |
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| Zusammenfassung |
| Recent work suggests that the quasi-periodic
(QP) modulation ~10–50 s of naturally occurring ELF-VLF radio emissions (~0.5–5
kHz) is produced by the compressional action of Pc3 magnetic pulsations on the
source of the emissions. Whilst it is generally accepted that these magnetic
pulsations have an exogenic source, it is not clear what the mechanism of their
generation is. A study of QP emissions observed during 1988 at Halley,
Antarctica, in conjunction with IMP-8 satellite solar wind data, shows that the
occurrence and modulation frequency of the emissions are strongly dependent upon
the direction and strength of the IMF, respectively. The observed relationships
are very similar to those previously reported for Pc3 pulsations associated with
upstream ion-cyclotron resonance, involving proton beams reflected at the
bowshock. In comparing the observed QP modulation frequencies with upstream wave
theory, agreement was found by considering wave excitation exclusively
associated with a proton beam reflected from a position on the bowshock at which
the shock normal is parallel to the ambient IMF direction. Other geometries were
found to be either impropitious or uncertain. The work indicates the useful
diagnostic role QP emissions could play in the study of compressional ULF waves
in the upstream solar wind and in monitoring the IMF conditions responsible for
their generation. |
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