Top panel: scatter plot of axial dipole moments of all active regions of cycles 21−24. The areas of the circles are proportional to the axial dipole moments of the active regions, and red and blue colors represent positive and negative axial dipole moments, respectively. Middle panel: rotational sums of negative and positive axial dipole moments for northern hemisphere. Bottom panel: rotational sums of negative and positive axial dipole moments for southern hemisphere. Vertical lines are axial dipole moment-weighted average emergence times of wings. Solid line is for the normal sign, dashed line for the opposite sign.