Fig. 4

Bias corrected forecasts of Gauss coefficients from differences between forecast sequences that start in 2016, 2017 and 2018. Each bias corrected forecast starts in the year of the later sequence. The solid line shows the 2020 forecast from the Goddard candidate model for IGRF-2020-SV, while the dashed (experiment A - experiment B), dash-dot (B-C) and dotted (A-C) lines show the bias corrected forecasts from our assimilation that use differences between the different forecast series. Panel a shows the coefficients for \(l=1\) and \(m=1\), while panel b shows the coefficients for \(l=2\), \(m=1\). Each panel shows the the bias corrected forecasts for \(G_l^m\) (upper) and \(H_l^m\) (lower) from Eq. 19