Butterfly diagram in the depth-time plane for the horizontally averaged toroidal magnetic field, B_y for Runs D04 and AR01. The dotted lines corresponds to the top (z = d) and base (z = 0) of the convection zone. The tilted dashed lines show approximate trajectories of buoyant magnetic fields. A rough estimate of rise speed is computed from these lines as indicated. The event at tu_rmsk_f = 9020 in the bottom panel is also shown in the top panels of Fig. 7.