Mean acceleration time ⟨t_acc(p)⟩ for our numerical model 1 and Bohm diffusion coefficient. The solid lines show calculations with Eqs. (15) and (1) for x_p. The colored lines are calculated with the spatial distributions of MHD parameters relevant to the time moments t shown in the legend. The dashed lines of the same color correspond to the same time moments and uniform flow, Eq. (14) with β_a = 6.67. The dotted horizontal lines are added to guide the eye; they correspond to the time moments shown in the legend.