Time evolution of B_z on the plane z = 0, corresponding to the average height of the optical surface (left panels) and the bolometric brightness (right panels) for the reference (2 × 2) case at 4 min (top), 80 min (middle), and 200 min (bottom) after introduction of the initial field. The average unsigned magnetic field for these snapshots corresponds to about 200 G, 50 G, and 10 G, respectively.