The Interplanetary Population of Suprathermal Ions from Impulsive Solar Energetic Particle Events: Solar Cycle Variations

摘要

Suprathermal ions in the solar corona or interplanetary medium play an important role in the determining the accelerated particle population produced by CME-driven shocks. Impulsive solar energetic particle events provide one of the sources of interplanetary suprathermals, and the presence of this material is detectable based on its unique composition in which the ion ~3He is normally enhanced by several orders of magnitude over its typical solar wind abundance. Using composition measurements made with instruments on NASA's Advanced Composition Explorer between 1997 and 2013 we have investigated the solar cycle variation of suprathermals from impulsive events over more than a full solar cycle. We find that the fraction of time with energetic ~3He detectable in the interplanetary medium near 1 AU dropped by more than a factor of 100 between the cycle 23 solar maximum and the following minimum. Comparison between the rising portions of cycles 23 and 24 shows that the fraction of time with ~3He present is significantly lower in the present solar cycle.