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| Titel |
THEMIS observations of compressional pulsations in the dawn-side magnetosphere: a case study |
| VerfasserIn |
G. I. Korotova, D. G. Sibeck, V. Kondratovich, V. Angelopoulos, O. D. Constantinescu |
| 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. 10 ; Nr. 27, no. 10 (2009-10-02), S.3725-3735 |
| Datensatznummer |
250016664
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| Publikation (Nr.) |
 copernicus.org/angeo-27-3725-2009.pdf |
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| Zusammenfassung |
| We present THEMIS-A low- and high-energy plasma, magnetic
field, and energetic particle observations of long period (11–36 min)
irregular compressional pulsations in the dawnside magnetosphere from 08:00
to 12:24 UT on 7 November 2007. We demonstrate that the pulsations maintain
thermal and magnetic pressure balance, then employ finite gyroradius
techniques to determine wave properties from the gyrophase distributions of
5–10 keV ions. The waves generally move sunward at velocities ~10 km s−1
with the background plasma convection flow. Wavelengths range from
6700 to 23 300 km, corresponding to azimuthal wavenumbers m from 18 to 76.
Wave periods decrease with increasing radial distance. Having determined the
parameters describing the waves, we consider three previously proposed
explanations: generation by substorm injection, generation by bounce or
drift-bounce instabilities, and generation by the drift-mirror instability.
The interval was quiet geomagnetically, arguing against any relationship to
substorm injections. We found that ions with low energies of 69–628 eV or
high energies of 28–615 keV would have been required to account for
drift-bounce resonance during this interval, but inspection reveals ion
fluxes at these energies near background levels during the time period
considered. On the other hand, the criteria for the drift mirror instability
are marginally satisfied. As predicted for the drift mirror instability,
particle distributions peak more sharply near 90° pitch angles during
magnetic field strength enhancements than during strength depressions. At
this point we therefore interpret the compressional pulsations observed by
THEMIS A in terms of the drift mirror instability. |
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