A. B. Galvin, E. Moebius, M. A. Popecki, L. M. Kistler, D. Morris, and D. Heirtzler Institute for the Study of Earth, Oceans an Space, and the Dept of Physics, Univ. of New Hampshire, Durham, NH 03824 USA D. Hovestadt, B. Klecker, A. Bogdanov MPE, Postfach 1603, D-85740 Garching, Germany B. Thompson NASA GSFC, Greenbelt MD, USA
Several Coronal Mass Ejection (CME) events observed by SOHO have an associated Gradual Solar Energetic Particle (SEP) event observed by L1 and near-earth spacecraft. Gradual SEPs show fractionation of source population (corona) abundances over photospheric abundances, typically organized by the first ionization potential (FIP). In addition, the Gradual SEP acceleration process introduces an energy and event dependent compositional bias organized by the element's mass per charge (A/Q). The SEPICA instrument on the ACE spacecraft determines the element (Z), energy (E) and ionic charge (Q) of energetic ions. Hence the A/Q of a given element is measured rather than inferred (Moebius et al., GRL, vol.26, 145, 1999). For selected SEP events occurring in 1997-1998, we present SEP abundance ratios of high (Ne, O), low (Mg, Si, Fe) and intermediate (C) FIP elements as a function of their measured mean A/Q and compare them to mean photospheric values.