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| Titel |
Quasi-parallel whistler mode waves observed by THEMIS during near-earth dipolarizations |
| VerfasserIn |
O. Contel, A. Roux, C. Jacquey, P. Robert, M. Berthomier, T. Chust, B. Grison, V. Angelopoulos, D. Sibeck, C. C. Chaston, C. M. Cully, B. Ergun, K.-H. Glassmeier, U. Auster, J. McFadden, C. Carlson, D. Larson, J. W. Bonnell, S. Mende, C. T. Russell, E. Donovan, I. Mann, H. Singer |
| 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. 6 ; Nr. 27, no. 6 (2009-06-08), S.2259-2275 |
| Datensatznummer |
250016542
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| Publikation (Nr.) |
 copernicus.org/angeo-27-2259-2009.pdf |
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| Zusammenfassung |
| We report on quasi-parallel whistler emissions
detected by the near-earth satellites
of the THEMIS mission before, during,
and after local dipolarization. These emissions
are associated with an electron temperature
anisotropy α=T⊥e/T||e>1
consistent with the linear theory
of whistler mode anisotropy instability.
When the whistler mode emissions are observed the
measured electron anisotropy varies inversely
with β||e
(the ratio of the electron
parallel pressure to the magnetic pressure)
as predicted by Gary and
Wang (1996).
Narrow band whistler emissions correspond to the small α existing
before dipolarization whereas the broad band emissions
correspond to large α observed during and after dipolarization.
The energy in the whistler mode is leaving
the current sheet and is propagating
along the background magnetic field, towards the Earth.
A simple time-independent description
based on the Liouville's theorem
indicates that the electron temperature
anisotropy decreases with the distance
along the magnetic field
from the equator.
Once this variation of α is taken
into account, the linear theory predicts
an equatorial origin for the whistler mode.
The linear theory is also consistent with the observed
bandwidth of wave emissions.
Yet, the anisotropy required to be fully consistent
with the observations is somewhat larger than the measured one.
Although the discrepancy remains
within the instrumental error bars,
this could be due to time-dependent
effects which have been neglected.
The possible role of the
whistler waves in the substorm
process is discussed. |
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