Authors: Bamert, K., R.F. Wimmer-Schweingruber, R. Kallenbach,
M. Hilchenbach, B. Klecker, A. Bogdanov, and P. Wurz
Reference: JGR, 107, 10129-10144, 2002
Abstract:
The SOHO/CELIAS/(H)STOF ((Highly) Suprathermal Time Of Flight) mass
spectrometer measures the elemental composition and the charge-state
distribution of ions with suprathermal energies in the range 10--4000 keV/amu from
above the solar wind particle distribution up to low-energy flare particle
energies. We analyze the time period around the large coronal mass
ejection (CME) event on May 2--3, 1998. Using data from (H)STOF we study the
charge-state distribution of He, the CNO group, and Fe. In addition, we investigate the energy dependence of the mean ionic charge
state of Fe in the energy-per-nucleon range 12--100 keV/amu. Furthermore,
we also report energy spectra of H$^{+}$, He$^{++}$, and He$^{+}$
and the variations in the elemental abundance ratios He/H, He/CNO, and
Fe/CNO. These observations greatly extend the energy range in which
particles associated with this time period have been measured. Because of
their elevated energies, suprathermal particles are the prime seed population for further acceleration in
gradual events. We identify interstellar pick-up ions as an important non-solar seed
population. The observed low mean ionic charge states of Fe and the small
Fe/CNO ratio are typical for large gradual events. The energy dependence
of the Fe charge states may be a result of the presence of different iron populations or of the thermal history of the
accelerated material. The temporal variations of Fe/CNO and He/CNO
indicate a stronger confinement of low-rigidity particles at the
acceleration site.