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| Titel |
Observation of energy-time dispersed ion structures in the magnetosheath by CLUSTER: possible signatures of transient acceleration processes at shock |
| VerfasserIn |
P. Louarn, E. Budnik, J. A. Sauvaud, G. Parks, K. Meziane, J. M. Bosqued, I. Dandouras, H. Rème, U. Mall, P. Daly, M. Dunlop, A. Balogh, L. M. Kistler, E. Amata |
| 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 ; 21, no. 7 ; Nr. 21, no. 7, S.1483-1495 |
| Datensatznummer |
250014656
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| Publikation (Nr.) |
 copernicus.org/angeo-21-1483-2003.pdf |
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| Zusammenfassung |
We analyse energy-time
dispersed ion signatures that have been observed by CLUSTER in the dayside
magnetosheath. These events are characterized by sudden increases in the ion
flux at energies larger than 10 keV. The high energy ions (30 keV) are first
detected, with the transition to the low energy ions (5 keV) lasting about 100
s. These injections are often associated with transient plasma structures of a
few minutes in duration, characterized by a hotter, less dense plasma and a
diverted flow velocity, thus presenting similarities with "hot flow
anomalies". They also involve modifications of the magnetic field
direction, suggesting that the shock interacts with a solar wind discontinuity
at the time of the event. The injections can originate from the magnetosphere
or the shock region. Studying in detail a particular event, we discuss this
last hypothesis. We show that the observed energy/time dispersion can be
explained by combining a time-of-flight effect with a drift of the source of
energetic particles along the shock. We propose that the acceleration results
from a Fermi process linked to the interaction of the discontinuity with a
quasi-perpendicular shock. This model explains the observed pitch-angle
selection of the accelerated particles. The Fermi process acting on the beam of
ions reflected from the shock appears to be sufficiently efficient to
accelerate over short time scales (less than 30 s) particles at energies above
30 keV.
Key words. Magnetospheric physics
(solar-wind-magnetosphere interaction; magnetosheath) – Space plasma physics
(shock waves) |
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