The 11- and 22-year modulation of galactic cosmic rays (GCRs) in the inner heliosphere is studied using a numerical model developed by Qin and Shen in 2017. Based on the numerical solutions of Parker's transport equations, the model incorporates a modified Parker heliospheric magnetic field, a locally static time-delayed heliosphere, and a time-dependent diffusion coefficients model in which an analytical expression of the variation of magnetic turbulence magnitude throughout the inner heliosphere is applied. Furthermore, during solar maximum, the solar magnetic polarity is determined randomly with the possibility of A > 0 decided by the percentage of the solar north polar magnetic field being outward and the solar south polar magnetic field being inward. The computed results are compared at various energies with several GCR observations, e.g., the Interplanetary Monitoring Platform 8 (IMP 8), EPHIN on board the Solar and Heliospheric Observatory (SOHO), Ulysses, and Voyager 1 and 2, and they show good agreement. We show that our model has successfully reproduced the 11- and 22-year modulation cycles.
