On cosmic ray modulation beyond the heliopause: where is the modulation boundary?

Abstract

Two of the paradigms in modeling the transport of galactic cosmic rays are that the modulation boundary is the heliopause and that the local interstellar spectra are identical to the galactic cosmic ray spectra. Here we demonstrate that the proton spectrum is already modulated due to an altered interstellar diffusion in the outer heliosheath as a consequence of the heliospheric “obstacle” in the interstellar flow. The main modulation effect however is adiabatic energy losses during a “confinement time” of cosmic rays inside the heliosphere.