Geomagnetic core field models in the satellite era

After a brief review of the theoretical basis and difficulties that modelers are facing, we present three recent models of the geomagnetic field originating in the Earth’s core. All three modeling approaches are using recent observatory and near-Earth orbiting survey satellite data. In each case the specific aims and techniques used by the modelers are described together with a presentation of the main results achieved. The three different modeling approaches are giving similar results. For a snap shot of the core magnetic field at a given epoch and observed at the Earth’s surface, the differences between models are generally small. They do not exceed 16 nT which gives an idea of the accuracy of the models. Secular variation models are robustly resolved up to spherical harmonic degree 13, but only on time scale as large as 10 years. On time scale of a year, secular variation models are resolved only up to degree 8 or 9. For higher time derivatives of core field models, only the very first degrees are robustly derived.