Suprathermal ions in quiescent periods at 1 AU in the 23rd and 24th solar-activity cycles

Abstract

The relative abundances of suprathermal (with energies ∼0.04–2 MeV/nucleon) 3He, 4He, C, O, and Fe ions and the energy spectra of 3He and Fe ions in near-Earth space during quiescent periods of solar activity are studied. Measurements obtained with the ULEIS instrument onboard the ACE spacecraft during the 23rd and 24th solar cycles are used. Substantial differences in the energy spectra of suprathermal ions in the 23rd and 24th solar cycles are observed for the selected quiescent periods. Appreciable differences in the energy dependences of the relative ion abundances are also found. One possible explanation for the results obtained is that the background ions were accelerated to suprathrmal energies under different conditions in the solar corona in these two cycles.