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| Titel |
QUIET-TIME INTERPLANETARY SUPERHALO ELECTRONS at SOLAR MINIMUM |
| VerfasserIn |
Linghua Wang, Robert Lin, Chadi Salem, Marc Pulupa, Davin Larson, Peter Yoon, Janet Luhmann |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250075052
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| Zusammenfassung |
| We present a statistical survey of ~2-20 keV superhalo electrons in the solar wind measured
by the SupraThermal Electron (STE) instrument onboard the two STEREO spacecraft, during
quiet-time periods from March 2007 through March 2009 at solar minimum. The observed
superhalo electrons have a nearly isotropic angular distribution and a power-law
spectrum, f - v-γ , with γ ranging from 5 to 8.7, with nearly half between 6.5 and
7.5, and an average index of 6.69±0.90. The observed power-law spectrum varies
significantly on a spatial scale of -³0.1 AU and temporal scale of -³days. The integrated
density of quiet-time superhalo electrons at 2-20 keV ranges from ~10-8 cm-3
to 10-6 cm-3, about 10-9 -10-6 of the solar wind density and it, as well as the
power-law spectrum shows no correlation with solar wind proton density, velocity or
temperature. The density of superhalo electrons decreases by approximately one
order of magnitude between early 2007 and early 2009, probably reflecting the
decay of solar cycle 23 and the approach to its unusually deep activity minimum,
while the power-law spectral index γ has no solar-cycle variation. These quiet-time
superhalo electrons are present even in the absence of any solar activity, e.g., active
regions, flares or microflares, type III radio bursts, etc., suggesting that they may be
accelerated by resonant wave–particle interactions in the interplanetary medium,
or by nonthermal processes related to the acceleration of the solar wind such as
nanoflares. |
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