Title: Origin of the May 1998 Suprathermal Particles: SOHO/CELIAS/(H)STOF Results

Authors: Bamert, K., R.F. Wimmer-Schweingruber, R. Kallenbach, M. Hilchenbach, B. Klecker, A. Bogdanov, and P. Wurz

Reference: JGR, 107, 10129-10144, 2002

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.

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Last Update: 21 January 2003, Xuyu Wang