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- Title
Solar Wind Suprathermal Electrons.
- Authors
Wang, Linghua; Yang, Liu; Tao, Jiawei; Li, Gang; Wimmer--‐Schweingruber, Robert; Bale, Stuart
- Abstract
Solar wind surpathermal particles carry important information on the common particleacceleration/transport processes at the Sun and in the IPM. We present a statistical survey ofsolar wind suprathermal electrons measured at ∼0.1-200 keV by the WIND 3DPinstrument at 1 AU during quiet times in solar cycles 23 and 24. All the strahl, halo andsuperhalo electron populations show no obvious correlation with the solar wind corepopulation. The halo electron population has an isotropic angular distribution, while the strahlpopulation, predominantly observed in fast solar wind, is antisunward beaming along theinterplanetary magnetic field. The observed energy spectrum of both strahl and halo electronsat ∼0.1-1.5 keV generally fits to a Kappa distribution function, with an index κ and effectivetemperature Teff. We find a strong positive correlation between κ and Teff for both strahland halo electrons and a strong positive correlation between the strahl density and halodensity, likely reflecting the nature of the generation of these electron populations. Inaddition, the strahl electron number density appears to positively correlate with both thesolar wind electron temperature and the IMF magnitude, in both slow and fast solarwind. For the superhalo electron population at quiet times, the observed pitch-angle distributionis generally isotropic, and the observed omnidirectional differential flux generally fits to apower-law function, J ∝ E−β. The spectral index β ranges from ∼1.6 to ∼3.7, with a broadmaximum between 2.4 and 2.8 (2.0 and 2.4) in solar cycle 23 (24). Both β andnsup show no obvious correlation with the sunspot number, solar flares, CMEs,etc. These results suggest that solar wind suprathermal electrons have a different origin fromthe solar wind core: the strahl could originate from the Sun, e.g., due to the escapingelectrons from the hot corona, to form a strong positive correlation between κ andTeff; the halo may be due to some processes (including scattering and/or furtheracceleration) acting on the strahl in the IPM; the superhalo may originate fromnonthermal processes related to the acceleration of the solar wind or could be formedin the IPM due to further acceleration and/or long-distance propagation effects.
- Subjects
SOLAR cycle; ELECTRONS; SOLAR flares; SOLAR corona; POSITRONS; SOLAR wind; MAGNETIC fields; ELECTRON temperature
- Publication
Geophysical Research Abstracts, 2019, Vol 21, p1
- ISSN
1029-7006
- Publication type
Article