G. M. Mason, J. E. Mazur, J. R. Dwyer University of Maryland, College Park, Maryland USA
We have measured the 3He abundance from ~0.5-2 MeV/nuc in 12 large solar energetic particle (SEP) events during the period November 1997 - June 1999. In 5 of the events, the 3He time-intensity profile is similar to the 4He time-intensity profile, indicating a common acceleration and transport origin for the two species. The average 3He/4He ratio during these events is 1.9 0.2 x 10-3, a factor of ~5 enhancement over the solar wind value. During this same survey period we have also measured the low energy ion intensities during quieter periods in-between the large particle events. We find 3He and Fe remnant from impulsive events present on a majority of the days, implying that they fill a substantial volume (>50%) of the in-ecliptic interplanetary medium during our survey. We suggest that these suprathermal ions may therefore be a source population that is available for further acceleration by interplanetary shocks that accompany large SEP events, thereby leading to the 3He enhancements in a significant fraction of large SEP events. This impulsive SEP event material might also account for recent observations of large solar particle events with energetic particle ionization states that have a wide range of ionization states that encompass values expected for both gradual and impulsive solar SEP events.