Energetic particle abundances at CIR shocks

The forward and reverse shocks that bound corotating interaction regions (C IRs) travel into different solar wind regimes. In order to test whether the energetic ions associated with the CIR shocks reflect the ambient solar wi nd, we investigate the elemental composition of 0.1-4.0 MeV/N ions in CIRs observed from 1 to 5 AU with instrumentation on board the Wind and Ulysses spacecraft. This is the first comparison of the abundances of energetic min or ions in CIR forward and reverse shocks. We find that apart from Helium ( and Neon at 1 AU) the energetic particle abundances are roughly in agreemen t with the respective solar wind thermal abundances. He is overabundant by a factor of 2.5 at the CIR reverse shock at distances of 4 to 5 AU, while t he forward shock abundance shows no He enhancement. There is no energy cuto ff for the He acceleration observed below 2.0 MeV/N at 2 to 5 AU. This resu lt is in qualitative agreement with models for pickup abundances in the inn er heliosphere and suggests that only pickup He dominates the suprathermal solar wind He spectrum in coronal high speed streams.