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| Titel |
Anomalous foreshock field-aligned beams observed by Cluster |
| VerfasserIn |
K. Meziane, A. M. Hamza, M. Wilber, C. Mazelle, M. A. Lee |
| 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 ; 29, no. 10 ; Nr. 29, no. 10 (2011-10-31), S.1967-1975 |
| Datensatznummer |
250017119
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| Publikation (Nr.) |
 copernicus.org/angeo-29-1967-2011.pdf |
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| Zusammenfassung |
| We report occasional observations of two simultaneously distinct ion
foreshock components recorded by the Cluster spacecraft upstream of the
Earth's bow shock. In most occurrences, the lower-energy population
originates as a field-aligned beam (FAB) associated with quasi-perpendicular
regions, which loses energy as the IMF rotates into oblique geometries. A
second beam, with energies in excess of ~10 keV, appears sometimes in
association with the onset of ultra-low frequency (ULF) waves, and sometimes
ahead of the appearance of the latter. Measurements from the mass
spectrometer indicate that both beams consist of protons. While the
lower-speed beam is well-accounted for by a known reflection mechanism, the
non-radial IMF orientations as well as other arguments seem to rule out
magnetosheath or magnetospheric sources for the higher energy component. The
wave characteristics are typical of the oblique foreshock and we have found
that they are in cyclotron-resonance with the low speed beam (FAB). These
observations constitute a theoretical challenge since conventional mechanisms
described in the literature cannot account for the production of beams at two
different energies. |
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