Physics – Plasma Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsh33a1828w&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #SH33A-1828
Physics
Plasma Physics
[7514] Solar Physics, Astrophysics, And Astronomy / Energetic Particles, [7859] Space Plasma Physics / Transport Processes, [7867] Space Plasma Physics / Wave/Particle Interactions
Scientific paper
We investigate pitch angle distributions (PADs) and temporal variations for five solar impulsive electron events with a rapid rise and rapid decay, observed by the WIND 3D Plasma & Energetic Particle instrument in the energy range from ˜0.3 to 300 keV. Below a transition energy E0 ( ˜10-30 keV), the PADs are highly anisotropic with a pitch-angle width at half maximum (PAHM) of <15o (unresolved) through the peak; the ratio of the peak flux of scattered (22.5-90o) to field-aligned scatter-free (0-22.5o, relative to the outward direction) electrons is <0.1. Above E0, the PADs become broader and the PAHM at peak increases with energy up to 85o at 300 keV; the peak-flux ratio of scattered to scatter-free electrons also increases with energy up to ˜0.8 at 300 keV. Thus, in these events, electrons with energies below E0 propagated essentially scatter-free through the interplanetary medium, while electrons at higher energies experienced pitch-angle scattering, with scattering strength increasing with energy. In the five events studied, the transition energy E0 between the two populations occurs where the electron gyroradius (ρ e) is equal to the local thermal proton gyroradius (ρ Tp), suggesting that the higher energy electrons were scattered by resonance with turbulent fluctuations at scale ≳ ρ Tp in the solar wind. In two events, the temporal profiles above 25 keV also show a second peak of inward-traveling electrons tens of minutes after the first peak, possibly due to reflection/scattering at ˜0.5-1 AU past the Earth, and a third peak due to outward-traveling electrons minutes later, likely caused by reflection/scattering of those inward-traveling populations between the Sun and Earth.
Krucker Sa"m
Lin Robert P.
Wang Lanjuan
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