Observed ΣA_S and ΣΦ_FN, YSK model (Eq. (1)) reconstruction of ΣΦ_FN from ΣA_S and H term in this model (Eq. (2)). (a) Composite time series of the total surface coverage by sunspots, ΣA_S, by Balmaceda et al. (2009). (b) Composite time series of the disc-integrated facular and network magnetic flux, ΣΦ_FN, by Yeo et al. (2014b) (black), the reconstruction of this quantity from ΣA_S with the YSK model (red), and the 365-day running mean of the difference between measurement and model (blue). The Balmaceda et al. (2009) time series goes back to 1874 but the range of the plot is confined to 1974 to 2017, the period where it overlaps with the Yeo et al. (2014b) time series. The gaps in the Yeo et al. (2014b) time series correspond to periods where there no suitable magnetogram observations with which to determine ΣΦ_FN were available. (c) The H term, which describes the response of ΣΦ_FN to the appearance of a sunspot per unit sunspot area. The dotted line follows the exponential envelope of H and t_⊙ denotes the synodic rotation period of the Sun (see Sect. 2.1 for details).