HR: 09:15h
AN: SH11A-05 INVITED     [PDF]
TI: Elemental and Isotopic Composition in Impulsive Solar\\ Energetic Particle Events: New Results from ACE
AU: * Wiedenbeck, M E
EM: mark.e.wiedenbeck@jpl.nasa.gov
AF: Jet Propulsion Laboratory, MS 169-327 4800 Oak Grove Dr., Pasadena, CA 91109 United States
AU: Leske, R A
AF: California Institute of Technology, MS 220-47 1200 East California Blvd., Pasadena, CA 91125 United States
AU: Cohen, C M
AF: California Institute of Technology, MS 220-47 1200 East California Blvd., Pasadena, CA 91125 United States
AU: Cummings, A C
AF: California Institute of Technology, MS 220-47 1200 East California Blvd., Pasadena, CA 91125 United States
AU: Mewaldt, R A
AF: California Institute of Technology, MS 220-47 1200 East California Blvd., Pasadena, CA 91125 United States
AU: Stone, E C
AF: California Institute of Technology, MS 220-47 1200 East California Blvd., Pasadena, CA 91125 United States
AU: von Rosenvinge, T T
AF: NASA Goddard Space Flight Center, Code 661, Greenbelt, MD 20771 United States
AB: Impulsive solar energetic particle (SEP) events, in which ion acceleration is thought to be associated with the energy release in solar flares, are characterized by large abundance enhancements of $^{3}$He and heavy nuclei. Models proposed to account for these fractionation patterns generally invoke some form of resonant wave-particle interaction to selectively heat and accelerate species with specific charge-to-mass ratios. Due to statistical limitations associated with the relatively low particle intensities in impulsive events, few such events have been studied in which precise abundance measurements could be obtained for a large number of species. However, several impulsive events in August 2002 were sufficiently intense above 10 MeV/nucleon to permit measurements by the Solar Isotope Spectrometer (SIS) on the Advanced Composition Explorer (ACE) of elemental abundances for most elements with atomic number Z$\le30$, as well as isotopic composition determinations for some of the more abundant elements such as Ne and Mg. Rather than having a fractionation pattern in which heavy ion enhancements increase monotonically with increasing Z, as is commonly ascribed to impulsive SEPs, these events exhibit some very significant enhancement differences between nearby elements (e.g., N/C, Ne/O, S/Ar, Fe/Ca) as well as between isotopes of individual elements (e.g., $^{22}$Ne/$^{20}$Ne, $^{26}$Mg/$^{24}$Mg) After reviewing the present understanding of composition in impulsive SEP events, we will present ACE/SIS observations of the August 2002 events, compare with previous observations of several events with unusual fractionation patterns, and discuss the constraints that these data place on models for particle acceleration. This research was supported by NASA at Caltech (under grants NAG5-6912 and NAG5-12929), JPL, and GSFC.
DE: 7514 Energetic particles (2114)
DE: 7519 Flares
SC: SPA - Solar and Heliospheric Physics [SH]
MN: 2003 Fall Meeting