The heliosphere dimensions and cosmic rays modulation

Cosmic Ray differential intensity at Earth has been reproduced using a 2D stochastic Montecarlo diffusion code and compared with measured data. We evaluated the effect of a stretched and compressed heliosphere on the Cosmic Ray fluxes at the Earth. We introduced a dependence of the diffusion parameter on the heliospheric size. We then found, for our 2D model, in comparison with experimental data, the optimum value of the heliospheric radius, which changes with time and solar activity. Differences in the heliospheric radius are effective only at energy below a few hundred MeV. Our results are in agreement with Voyager measurements and with models of heliospheric size modulation.