Anomalous Cosmic Rays

Modulation of GCR in the Heliosphere
Anomalous Cosmic Rays (ACRs) are a low-energy component of interplanetary particles that include the elements H, He, C, N, O, and Ar. They are now known to originate from interstellar neutral particles that have been swept into the heliosphere, ionized by solar UV or charge exchange with the solar wind, convected into the outer heliosphere, and then accelerated to energies of about 10 MeV/n or more. It is commonly assumed that the bulk of ACR acceleration takes place at the solar wind termination shock.

Spectra of Energetic Oxygen Nuclei The observation of the anomalous N, O, and Ne ionic charge composition with the SAMPEX satellite confirmed the theoretical predictions that ACRs are only partially charged; more precisely, singly charged ions dominate only at energies below 20 MeV/n, while at higher energies multiply charged ions become more abundant.
Being only partially ionized, ACRs have a much greater magnetic rigidity (at a given energy per nucleon) than either GCRs, which are essentially fully stripped, or SEPs, which have charge states characteristic of coronal temperatures. As a result, ACRs can be observed to much lower invariant latitude with a polar orbiting spacecraft like NINA.