33RD INTERNATIONAL COSMIC RAY CONFERENCE, RIO DE JANEIRO 2013 THE ASTROPARTICLE PHYSICS CONFERENCE The Solar-cycle Variation of 3He from Solar Energetic Particle Events

Abstract: A study of the frequency of occurrence of enhancements of energetic 3He from impulsive solar energetic particle events has been carried out using data from the ULEIS and SIS instruments on the Advanced Composition Explorer spacecraft. The data set, which currently extends over a 15+ year period from late 1997 through early 2013, shows rapid increases in the fraction of time that 3He was observable during both solar cycle 23 and cycle 24. Averaged over the first three years of cycle 24 the fraction of time with 3He detected was significantly less than for a comparable period in cycle 23. Over the period of this study, the variation of 3He exhibited a better correlation with sunspot number than with several other parameters that were investigated