Fig. 3

Geomagnetic power spectra for the main field (MF, in \(\text {nT}^2\)), secular variation (SV, in \(\text {nT}^2\)/\(\text {year}^2\)) and secular acceleration (SA, in \(\text {nT}^2\)/\(\text {year}^4\)) for 2015.0 for the Mag.num IGRF parent model compared to the CHAOS6-x9 model