Other
Scientific paper
May 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agusmsh23b..03l&link_type=abstract
American Geophysical Union, Spring Meeting 2004, abstract #SH23B-03
Other
2118 Energetic Particles, Solar, 7514 Energetic Particles (2114)
Scientific paper
During this solar cycle we have found that solar energetic particle (SEP) isotopic composition in large gradual events can vary greatly from event to event. It is an open question how much of this fractionation is present in the source material and how much occurs during particle acceleration or propagation out of the corona. To first order, this mass fractionation seems to scale as a power law in the ionic charge to mass ratio, Q/M, similar to what is observed for SEP elemental fractionation. However, differences from power-law scaling seem to be required for most events to completely account for the observed abundances, for example in the case of Fe isotopes. Determining the actual fractionation patterns is necessary in order to use these data to better constrain the coronal source abundances and to understand the fractionation processes. In the >6 years since the launch of NASA's Advanced Composition Explorer (ACE), we have obtained SEP isotope measurements of abundant elements from C to Ni in >40 large SEP events. We find that the isotopic and elemental abundance enhancements are strongly correlated. By assuming isothermal conditions and using calculated equilibrium charge states, we attempt to characterize deviations in the fractionation patterns from simple power-law scaling. This work was supported by NASA at Caltech (under grants NAG5-6912 and NAG5-12929), JPL, and GSFC.
Cohen M. C.
Cummings Alan C.
Leske Richard A.
Mewaldt Richard A.
Stone Edward C.
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