Suprathermal Ion Abundance Variations in Corotating Interaction Regions over Two Solar Cycles

Abstract

Abstract Suprathermal ion composition associated with corotating interaction regions (CIRs) exhibited a solar cycle variation during solar cycle 23 and the beginning of solar cycle 24. However, it is unclear if this variation would remain when considering all of solar cycle 24, or whether the variations in the CIR-associated suprathermal ion composition would change. Using 20 yr of Advanced Composition Explorer observations (1998–2018), we present a comparison of the suprathermal ion compositions for solar cycles 23 and 24. The energetic particle content for the two solar cycles is found to be remarkably similar. The observed solar cycle variations in 0.32–0.45 MeV/nuc Fe/O previously observed for solar cycle 23 was seen to be largely repeated in solar cycle 24, both in solar cycle phase and magnitude. A small enhancement in CIR-associated Fe/O during the declining phase was observed for both solar cycles. The CIR event-averaged intensities of Fe and O were also found to have a slight solar cycle dependence, with the Fe/O ratio being more closely bound to the intensity of Fe ions. Additionally, the elemental abundance versus O ratios compared to the Fe/C ratios were found to follow the same trends for both solar cycles, with high Fe/C ratio events occurring mostly during solar maximum.