Time Variations in the Fluxes of Suprathermal Ions and Their Relative Abundances at 1 AU during 1998–2017

Abstract

Time variations in the fluxes of the suprathermal (0.04–2 MeV/nucleon) ions ³He, ⁴He, C, O, and Fe are studied together with their relative abundances in the 23rd and 24th solar cycles (SCs) using data from the ULEIS instrument on board the ACE spacecraft. Positive correlations are found between the intensities of these ions detected at 1 AU and parameters of solar activity, indicating that these suprathermal ions originate predominantly in active processes on the Sun. The intensities of all ions at the activity maximum were lower in SC 24 than in SC 23, in both perturbed and quiescent periods of these cycles. In contrast, the time behaviors of the ratios ³He/⁴He, C/O, and Fe/O were different, and dependent on the primary ionization potential of the ions. The distribution of Fe/O shows higher medium and median values in SC 23, while the distributions of C/O and ³He/⁴He for SC 23 and SC 24 did not display appreciable differences. The results obtained suggest that the fluxes of Fe ions from the Sun during flares and in the corona were lower in SC 24 than in SC 23 to a greater extent than were the fluxes of ³He, ⁴He, C, and O ions.