Fig. 2From: A candidate secular variation model for IGRF-13 based on MHD dynamo simulation and 4DEnVar data assimilationSecular variation time scale of our dynamo model. The time scale of secular variation for each spherical harmonic degree \(\tau_{l}\) is fitted by \(\tau_{SV}^{*} /l\) for \(l \ge 2\). The resulting \(\tau_{SV}^{*}\) is 0.0411, which was utilized to scale the dimensionless numerical dynamo timeBack to article page