Fig. 3

Energy spectra at the Earth’s surface in 2015.0 associated with the main field (left) and the secular variation (right). Thin gray lines and symbols and thick black lines and symbols, correspond to the solutions of the Kalman filter and the smoothing algorithms, respectively. The thin black lines and symbols are associated with the outcomes of a 2010.0–2015.0 forecast simulation. Continuous and dashed lines are assigned to the energy spectra of, respectively, the different mean solutions and their associated standard deviation. Triangles and circles represent the spectra of the difference between the Kalmag mean models and the DGRF model in 2015.0 for the main field and the CHAOS-6.9 model of Finlay et al. (2016) for the secular variation, respectively. The inserted color maps correspond to the radial component of the core field (left) and the secular variation (right) at the core mantle boundary. They are from the 2015.0 smoothing solution expanded up to SH degree \(\ell =20\)