Variable fractionation of solar energetic particles according to first ionization potential
The average composition of solar energetic particles (SEPs), like the solar corona, is known to be depleted in elements with first ionization potential (FIP) more than ~10 eV by a factor of approximately four. We examine evidence for event to event variations in the FIP-related fractionation of SEPs, following up a 1994 study by Garrard and Stone. In a survey of 46 SEP events from 1974 to 1999 the deduced FIP-fractionation varies by a factor of ~2 from event to event, with no apparent relation to charge-to-mass dependent fractionation patterns in these same events. These results are compared to similar variations observed in the solar wind.
Additional Information© 2000 American Institute of Physics. Issue Date: 15 September 2000. This work was supported by NASA at the California Institute of Technology (under grant NAS5- 6912), the Jet Propulsion Laboratory, and Goddard Space Flight Center.
Published - MEWaipcp00b.pdf