Other
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufmsh43b1519l&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #SH43B-1519
Other
2114 Energetic Particles (7514), 7513 Coronal Mass Ejections (2101), 7514 Energetic Particles (2114)
Scientific paper
Solar energetic particles (SEPs) provide a direct sample of the Sun from which the solar composition may in principle be determined. Using high-resolution measurements from the Solar Isotope Spectrometer (SIS) onboard NASA's Advanced Composition Explorer (ACE) spacecraft, we have studied the isotopic composition of SEPs at energies >20 MeV/nucleon in large SEP events. We present SEP isotope measurements of C, O, Ne, Mg, Si, S, Ar, Ca, Fe, and Ni made in nearly 50 large events from the launch of ACE in late 1997 to the present. Obtaining the underlying source composition is complicated by the fact that the isotopic composition is highly variable from one SEP event to another due to mass fractionation that presumably occurs during the acceleration and/or transport of these particles. Although elemental abundances are often strongly energy dependent, we find little evidence of any energy dependence in the isotopic composition over the limited energy interval of this study. However, we find that various isotopic and elemental enhancements are correlated with each other in a manner indicating that the fractionation scales approximately as a power law in the ionic charge to mass ratio. This allows us to derive empirical corrections to account for the compositional variability and obtain estimated solar isotopic abundances. We compare the solar values and their uncertainties inferred from SEPs with those that are available from solar wind and meteoritic measurements and find generally good agreement. This work was supported by NASA at Caltech (under grant NAG5-12929), JPL, and GSFC.
Cohen M. C.
Cummings Alan C.
Leske Richard A.
Mewaldt Richard A.
Stone Edward C.
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