Fig. 1

A schematic figure of the 4DEnVar and prediction of the future geomagnetic field. The weighted sum of an ensemble of dynamo run (the thick blue line) is the final estimate after the assimilation corresponding to Eq. 13. The SV candidate model for IGRF-13SV (the red dashed line) is determined by line-fitting to the MHD expectation of the next 5 years. One can use geomagnetic data up to ~ 6 months before the release of IGRF for generation of candidate models because the deadline of their submissions is ~ 3 months before the release (October 1st for IGRF-13)