Authors: P. Wurz, P. Bochsler, and M.A. Lee
Reference: J. Geophys. Res. 105 (A12), (2000), 27239-27251
Abstract:
For the coronal mass ejection (CME) of January 6, 1997, strong
element fractionation of the heavy ions was observed with the
SOHO/CELIAS/MTOF instrument at 1~AU. During the passage of the CME
plasma and the passage of the erupted filament, which followed the
CME, a mass-dependent element fractionation was found with an
enhancement of heavy elements, increasing monotonically
with atomic mass. Si/O and Fe/O ratios around 0.5 were
observed, which corresponds to an increase of about a factor of four
compared to regular slow solar wind. We present a theoretical model
with which we can reproduce the observed element fractionation. The
model assumes hot coronal loops with non-Maxwellian electron
distributions as the precursor structure of the CME on the solar
surface. Diffusion perpendicular to the magnetic field
results in the preferential loss of lighter ions from the loop,
leading to mass fractionation. To quantitatively reproduce the
fractionation process the loops must have existed for about 28
hours before they became part of the CME plasma, a time which is
commensurate with optical observations of loops in the active
region from which the CME was launched.