A Study of Pitch Angle Distributions for Six Solar Impulsive Electron Events

Details A Study of Pitch Angle Distributions for Six Solar Impulsive Electron Events A Study of Pitch Angle Distributions for Six Solar Impulsive Electron Events

Dec 2006

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmsh43b1530w&link_type=abstract

American Geophysical Union, Fall Meeting 2006, abstract #SH43B-1530

Statistics

7514 Energetic Particles (2114), 7519 Flares, 7859 Transport Processes

Scientific paper

The pitch angle distributions (PADs) of solar impulsive electron events measured at 1 AU provide important information on the solar release of the electrons and their interplanetary transport. Using WIND/3DP electron data, we investigate the energy and time dependence of the PADs for six impulsive electron events with short time durations, low pre-event background, good count statistics and the electron energy range from ~0.5 keV to ~200 keV. The PADs of the pre-event background are anisotropic below ~2 keV due to halo electrons continuously streaming out from the Sun at these energies and isotropic above. In the preliminary study of two events (1998 Aug 29 and 2002 Oct 20), we remove such pre-event background. We find that the PAD width at half maximum is roughly constant from ~0.5 keV to 10-13 keV. It remains below ~30 degrees and changes slightly through the rapid-rise, rapid-decay phase, and it increases up to ~50-60 degrees at the slow-decay phase. We also find that the PAD width above ~13-20 keV increases with both energy and time. At the peak phase the width increases from ~40-50 degrees at 30 keV to ~60-70 degrees at 200 keV. At 200 keV it increases from ~50-60 degrees at the rapid-rise phase to ~80 degrees at the slow-decay phase. These properties suggest that, for these solar impulsive electron events, the low-energy electrons propagate nearly scatter-free in the interplanetary medium, while the high energy electrons experience some energy-dependent scattering. Furthermore, at a fixed energy, after electrons are scattered to different pitch angles, they travel to 1 AU at different speeds parallel to the magnetic field line. We analyze the pitch-angle dispersion and estimate the distance between the scattering site and 1 AU. We find that for high-energy electrons the average is ~0.03±0.06 AU.

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