Suprathermal helium in corotating interaction regions: combined observations from SOHO/CELIAS/STOF and ACE/SWICS

Abstract

Context. Energetic particle enhancements that are associated with corotating interaction regions (CIRs) are typically believed to arise from the sunward propagation of particles that are accelerated by CIR-driven shocks beyond 1 AU. It is expected that these sunward-travelling particles will lose energy and scatter, resulting in a turnover of the energy spectra below ~0.5 MeV/nuc. However, the turnover has not been observed so far, suggesting that the CIR-associated low-energy suprathermal ions are accelerated locally close to the observer.