Taking into consideration that the diffusion coefficient, κ, is supposed to be roughly inversely related to the
strength of the
interplanetary magnetic field (Wibberenz et al. 2001b), which in turn is directly related, but not necessarily linearly proportional, to the OSF, one can assume that the modulation potential is roughly proportional to the OSF, ϕ ∝ F n (Usoskin et al. 2002).