Transport equation of the galactic cosmic ray (GCR) is numerically solved for qA>0 and qA<0 based on the stochastic differential equation (SDE) method. We have developed a fully time-dependent and three-dimensional code adapted for the wavy heliospheric current sheet (HCS). Results anticipated by the drift pattern are obtained for sample trajectories and distributions of arrival points at the heliospheric boundary for GCR protons. Our simulation reproduced a 22-year cycle of solar modulation which is qualitatively consistent with observations. Energy spectra of protons at 1 AU are calculated and compared with the observation by BESS.
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