G.C. Ho, E.C. Roelof, R.E. Gold, S.M. Krimigis The Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA G.M. Mason, J.R. Dwyer Department of Physics, University of Maryland, College Park, MD 20742, USA J.E. Mazur The Aerospace Corporation, Los Angeles, CA 90009, USA
Using both the EPAM and ULEIS instruments on ACE, we investigated from November 1997 to May 1999 a total of 66 3He-rich solar energetic particle (SEP) events. The majority of these events (~68%) have a clear association with energetic electrons (38-53 keV) but a significant portion (~15%) has no detectable energetic electrons. For those events in which energetic electrons were detected, an inverse correlation was found between the maximum electron event intensities and the event-average 3He/4He (0.3 - 0.5 MeV/nuc.) ratios. We have found that SEP events with high 3He/4He (> 1) ratios in general do not have high electron intensities. Conversely, SEP events with small 3He/4He (< 0.1) ratios usually have higher electron intensities. In addition, the event average 3He/4He and Fe/C ratios are clearly correlated. This result differs from those of previous studies that used data at higher energy with less sensitivity. This correlation suggests that the 3He and Fe enrichments could be related and places further constraints any 3He-enhancement models.