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| Titel |
Statistics of counter-streaming solar wind suprathermal electrons at solar minimum: STEREO observations |
| VerfasserIn |
B. Lavraud, A. Opitz, J. T. Gosling, A. P. Rouillard, K. Meziane, J.-A. Sauvaud, A. Fedorov, I. Dandouras, V. Génot, C. Jacquey, P. Louarn, C. Mazelle, E. Penou, D. E. Larson, J. G. Luhmann, P. Schroeder, L. Jian, C. T. Russell, C. Foullon, R. M. Skoug, J. T. Steinberg, K. D. Simunac, A. B. Galvin |
| 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 ; 28, no. 1 ; Nr. 28, no. 1 (2010-01-22), S.233-246 |
| Datensatznummer |
250016758
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| Publikation (Nr.) |
 copernicus.org/angeo-28-233-2010.pdf |
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| Zusammenfassung |
| Previous work has shown that solar wind suprathermal
electrons can display a number of features in terms of their anisotropy. Of
importance is the occurrence of counter-streaming electron patterns, i.e.,
with "beams" both parallel and anti-parallel to the local magnetic field,
which is believed to shed light on the heliospheric magnetic field topology.
In the present study, we use STEREO data to obtain the statistical
properties of counter-streaming suprathermal electrons (CSEs) in the
vicinity of corotating interaction regions (CIRs) during the period March–December 2007.
Because this period corresponds to a minimum of solar
activity, the results are unrelated to the sampling of large-scale coronal
mass ejections, which can lead to CSE owing to their closed magnetic field
topology. The present study statistically confirms that CSEs are primarily
the result of suprathermal electron leakage from the compressed CIR into the
upstream regions with the combined occurrence of halo depletion at 90°
pitch angle. The occurrence rate of CSE is found to be about 15–20% on
average during the period analyzed (depending on the criteria used), but
superposed epoch analysis demonstrates that CSEs are preferentially observed
both before and after the passage of the stream interface (with peak
occurrence rate >35% in the trailing high speed stream), as well as
both inside and outside CIRs. The results quantitatively show that CSEs are
common in the solar wind during solar minimum, but yet they suggest that
such distributions would be much more common if pitch angle scattering were
absent. We further argue that (1) the formation of shocks contributes to the
occurrence of enhanced counter-streaming sunward-directed fluxes, but does
not appear to be a necessary condition, and (2) that the presence of
small-scale transients with closed-field topologies likely also contributes
to the occurrence of counter-streaming patterns, but only in the slow solar
wind prior to CIRs. |
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