  We present the newly developed stochastic model of the galactic cosmic ray
(GCR) particles transport in the heliosphere. Mathematically Parker transport
equation (PTE) describing non-stationary transport of charged particles in the
turbulent medium is the Fokker-Planck type. It is the second order parabolic
time-dependent 4-dimensional (3 spatial coordinates and particles
energy/rigidity) partial differential equation. It is worth to mention that, if
we assume the stationary case it remains as the 3-D parabolic type problem with
respect to the particles rigidity R. If we fix the energy it still remains as
the 3-D parabolic type problem with respect to time. The proposed method of
numerical solution is based on the solution of the system of stochastic
differential equations (SDEs) being equivalent to the Parker's transport
equation. We present the method of deriving from PTE the equivalent SDEs in the
heliocentric spherical coordinate system for the backward approach. The
obtained stochastic model of the Forbush decrease of the GCR intensity is in an
agreement with the experimental data. The advantages and disadvantages of the
forward and the backward solution of the PTE are discussed.
