Comparison of the simulation results of the open magnetic flux with observations. The red, blue and green curves are the mean results of 100 realisations used as input to the SFTM for AMR, LMR and SMR, respectively. The top panels show the best-fit run with R_cusp = 1.4 R_⊙ while the bottom panels show the run with R_cusp = 1.5 R_⊙. The shaded areas are the standard deviations. The results from the RGO/SOON record are shown by the dash-dotted purple line. (a) and (c) Reconstruction of the (1-year smoothed) open magnetic flux from the CSSS model over cycles 20–24. The black line is the reconstruction from the geomagnetic aa-index by Lockwood et al. (2022) and the dark green dashed line shows the in-situ measurements by Owens et al. (2017). (b) and (d) Same but over the entire period from 1874 to 2020.