HR: 14:35h
AN: SH53B-04    [Abstracts]
TI: Upper Limit on ³He Fluence in Solar Energetic Particle Events
AU: * Ho, G C
EM: George.Ho@jhuapl.edu
AF: Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, United States
AU: Mason, G M
AF: Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, United States
AU: Roelof, E C
AF: Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Road, Laurel, MD 20723, United States
AB: We have investigated more than 260 ³He-rich (³He/⁴He > 0.004 at 0.2-2.0 MeV/nucleon) solar energetic particle (SEP) events from September 1997 through December 2006 using the ULEIS instrument on ACE. Both "impulsive" (flare-related) and "gradual" (CME-related) events are included. The ³He fluences varied only by a factor of 100 above our instrument sensitivity threshold while the 4He fluences varied by factor of 10,000 above the same threshold. Moreover, there appears to be no significant correlation between the ³He and ⁴He fluences. We find it striking that with more than 9 years of continuous SEP data, we could not find any SEP event that has a ³He fluence higher than 2.0×10⁵/cm2-sr-MeV/nucleon, while the largest ⁴He fluence observed was 7.0×10⁷/cm2-sr-MeV/nucleon. In the approximation that the event fluence is proportional to the net particle outflow from the Sun, the observed upper limit for the ³He fluence seems to indicate that only limited outflow of 0.2-2 MeV/nucleon ³He can be released from the Sun in a SEP event.
DE: 7807 Charged particle motion and acceleration
DE: 7845 Particle acceleration
DE: 7846 Plasma energization
SC: SPA-Solar and Heliospheric Physics [SH]
MN: 2007 Fall Meeting