a) Modelled total magnetic flux (solid red), 0.68Φ_AR + 0.4Φ_ER (see Sect. 3.3), compared with the observations from the Wilcox Solar Observatory (blue triangles) and the Mount Wilson Observatory (black squares). The vertical dashed line indicates the time when the data from the Mount Wilson observatory become available. b) Modelled magnetic flux from active regions (0.68Φ_AR; solid blue), ephemeral regions (Φ_ER; dashed blue), and the total magnetic flux (0.68Φ_AR + Φ_ER; solid black).