The Sun moves through the local interstellar medium (LISM) and modifies its properties to heliocentric distances as large as 1 pc, especially if the effect of the heliosphere on the transport of multi-TeV Galactic cosmic ray (GCR) fluxes is concerned.
The solar wind (SW) inside the heliosphere is affected by the penetrating LISM neutral atoms. Charge exchange between the LISM atoms and SW ions creates non-thermal, pickup ions and secondary neutral atoms, the latter propagating deeply into the LISM. Observational data from the IBEX, New Horizons, and Voyager spacecraft, as well as numerous air shower experiments, convincingly demonstrate that the heliosphere modulates Galactic Cosmic Rays (GCRs) up to extremely high energies.
From the GCR transport perspective, it is important to understand the structure of the heliosphere, properties of the turbulent solar and LISM plasma, and distributions of magnetic field throughout the interaction region. We discuss observations and simulations that shed light onto the mutual influence of the SW and LISM. We also describe the physical phenomena that accompany the SW–LISM interaction, analyze the coupling of the heliospheric and interstellar magnetic field at the unstable surface of the heliopause, and discuss their effects on GCR modulation in the outer heliosheath. We propose a new model, which is implemented in a box of 12,000 au cubed, extends far into the heliotail region, and is necessary for the explanation of TeV GCR anisotropy measurements.