Distance to the solar wind termination shock and the source flux of anomalous cosmic rays during 1986‐1988

Abstract

We use observations of the intensity of anomalous cosmic ray helium and oxygen in the outer heliosphere near the last solar minimum period, in conjunction with solar observations of the tilt of the neutral current sheet, to estimate that the solar wind termination shock was at 67 ± 5 AU during the time period 1986.7‐1988.5. We find the source flux of anomalous cosmic rays at the shock to be 1.7 ± 0.3 (m² s sr MeV/nucleon)−1 for 7.1‐17.1 MeV/nucleon anomalous cosmic ray oxygen and 4.3 ± 0.8 (m² s sr MeV/nucleon)−1 for 31‐57 MeV/nucleon anomalous cosmic ray helium. We also estimate a source flux of anomalous cosmic ray hydrogen of 2.3 ± 0.6 (m² s sr MeV)−1 at 134 MeV. The resulting energy density of anomalous cosmic rays at the solar wind termination shock is ∼0.03 eV/cm³, approximately 2% of the energy density of the solar wind at 67 AU.