The effects of anomalous cosmic rays on the geometry of outer heliosphere from a numerical simulation

We conduct a global MHD-neutrals-cosmic rays simulation to investigate the effects of anomalous cosmic rays on the large-scale structure of outer heliosphere. In the model, the anomalous cosmic rays is treated as a massless fluid and only contributes the pressure. Because of the nearly non-scattering environment in outer heliosphere, the diffusion coefficients for cosmic rays are extremely larger than those in the heliosphere, which is difficult to be implemented in a numerical simulation. We propose a new boundary condition to overcome this difficulty. The results show that the cosmic rays significantly modify the structure of outer heliosphere. Compared to the simulation without cosmic rays, the width of inner heliosheath along Voyager 1 direction is substantially reduced to ∼ 30AU, which is consistent with the observations. In addition, we find that the cosmic ray affect the radial distances of termination shock, the respective crossings of the shocks by the two Voyager probes could be explained by the effects of cosmic rays in various diffusion environments. Our numerical results indicate that the effect of cosmic rays is an important factor for the global structure of outer heliosphere in a numerical simulation.