Understanding and forecasting Earth’s magnetic field variations through numerical simulation

The Earth’s magnetic field varies in time, and the past two decades have seen tremendous progress in understanding these variations. This has been achieved through numerical modelling of the geodynamo equations describing how the convecting liquid core of the Earth sustains the geomagnetic field. Though such models are still far from the parameter regime relevant to the natural system, they are now capable of reproducing the field morphology, most of its temporal variations and the underlying core flows. It is thus now natural to use them as a source of prior information to inverse problems aiming at determining the internal structure of the geodynamo from surface observations, and in forecasts schemes aiming at determining its future evolution. In this presentation, I will summarise some key results in the history of direct numerical geodynamo modelling, before introducing the basics of modern inverse modelling. In a final part, I will finally show how these tools provide insight into the mechanisms at the origin of the present decay of the geomagnetic dipole, before turning to our predictions for the evolution of Earth’s magnetic field in the coming century.