Particle densities drawn in grey shades on top of the radial velocity profile of the background solar wind, 16 h after the particle injection (online movie). The left and right panels correspond to the cases without and with perpendicular diffusion, respectively. The solid orange and dashed black lines represent magnetic field lines, drawn with a constant longitudinal separation of 3.5° at r = 1 AU. The markers correspond to the location of the different observers discussed in the text.