Anomalous Cosmic Ray Spectra in the Outer Heliosphere: 1992-1998

As the Voyager 1 and 2 spacecraft travel through the outer heliosphere, the Low Energy Charged Particle instruments onboard have been making composition measurements of energetic ions above about 0.3 MeV/nucleon. During the years 1992 through 1998, a period of declining solar modulation in the outer heliosphere, V1 traveled from 47 to 72 AU and V2 traveled from 36 to 57 AU. We have constructed annual energy spectra for several ACR species that, in general, show monotonic flux increases over that period, typically by a factor of about 100 for the flux near the ACR spectral peaks. This increase appears to be largely temporal rather than spatial. These observations have implications for ACR acceleration and transport.