MHD snapshots for case 1b (Table 1) – a single sinusoidal perturbation in a wide box. Left to right panel: magnetic field lines B with J_z contours, magnetic field lines with B_z contours and the plasma flow v. Arrows on v plots indicate the in-plane velocity direction. Snapshots (panel a) through (panel f) correspond to times t = 0, 8, 64, 112, 144 and 300τ_A. Note that the aspect ratio is not to scale – the width of the domain 16 in x and 2 in y. The colour scheme is adaptive to enhance contrast. Note that colour representing zero is consistent across similar plots throughout.