(Top) Time-evolution of vertical magnetic field strength B_z/B₀ at the surface z/H₀ = 0 (magnetogram). White (black) indicates the positive (negative) polarity. (Bottom) Corresponding velocity fields (Dopplergram). The vertical velocity V_z/C_s0 (color; red is downward) and the horizontal velocity V_h/C_s0 (arrows) are shown. Corresponding vertical field B_z/B₀ at the photosphere is over-plotted with contours.