Fig. 9

Radial field to degree 13, radial secular variation (SV) and radial secular acceleration (SA), both to degree 16, at the core surface in 2015. Units are \(\hbox {mT}=10^{6}\hbox {nT}\), \(\mu \hbox {T/year}=10^3\hbox {nT/year}\) and \(\mu \hbox {T/year}^{2}=10^{3}\hbox {nT/year}^2\). Map projection is Hammer-Aitoff