Time series of the average of the unsigned vertical flux density, smoothed with a 1-month wide time window (solid lines). Left panel: averaging over the disk region r/r_⊙ < 0.1. Right panel: averaging over the disk region r/r_⊙ < 0.9. The dashed curves use a second-order polynomial in the sunspot number (also smoothed with a 1-month time window) to fit the solid curves. The fit gets tighter as the disk averaging area increases.