Interplanetary Propagation of Solar
Impulsive Energetic Electrons
Linghua Wang, Bob Lin and Säm Krucker
Space Sciences Lab, UC Berkeley
SSL
UC Berkeley
2010 June
ACE/SOHO/STEREO/Wind Workshop
ρe = ρTp
Summary for the five events
*Two different PAD behaviors at low
and high energies:
At low energies (~0.3keV to E0),
the PAHM remains roughly constant
below 30° (corresponding to an actual
PAHM of <~15°, limited by the
instrumental response) from onset
through the peak.
At high energies (E0 to ~300 keV),
the PAHM increases with energy, e.g.,
from ~30° at E0 up to 85° at 300 keV
at the peak; it also increases with time.
The energy transition E0 varies from
~10 to 30 keV, from event to event.
Summary for the five events
The ratio Λ of the peak flux of outward-traveling scattered electrons to field-aligned scatterfree electrons
* Although the energy transition E0 varies
from ~10 to 30 keV and the Tp varies from
~7 to 33 eV, the E0 always corresponds to a
ρe0 ~ 0.7-1.2 ρTp.
Summary for the five events
The ratio Λ of the peak flux of outward-traveling scattered electrons to field-aligned scatterfree electrons
At energies with ρe < ρTp, electrons would
be weakly scattered because of weak power
densities for resonant fluctuations/waves at
scale λ < ρTp (the dissipation range).
At energies with ρe > ρTp, electrons
would scatter more due to stronger power
densities for fluctuations/waves at scale λ >
ρTp (the inertial range), and the power-law
increase of Λ with ρe may be associated
with the power-law increase of turbulence
power density with λ (P  λβ) .
Summary for the five events
* For high-energy electrons, the observed flux-time profiles retain a rapid-rise,
rapid-decay peak and the estimated path length is only ~4-18% longer than the
smooth spiral field length, indicating that strong scattering, if it existed within 1
AU, only occurred near 1 AU since strong scattering (mean free path <~ 0.4
AU) throughout the inner solar system would produce a fast-rise, very slowdecay (with the e-folding decay time of > 4hours for mean free path <~ 0.4 AU)
peak [Lin, 1974] and a much larger path length.
Such propagation cannot explain the previously reported delay of ~10-30 min
for high-energy electrons [Krucker et al., 1999; Haggerty & Roelof, 2002;
Wang et al., 2006]. Thus, this delay must reflect the actual delay in the solar
injection of high-energy electrons.