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Abstract

A major source of time-varying magnetic fields are external ionosphere-magnetosphere currents and associated fields induced in subsurface and oceans. Induced fields may bias external and core field models if not accounted for in a physically consistent manner. In addition, induced fields contain unique information on the subsurface conductivity distribution. Yet, induced fields are often considered noise (and neglected) or at best treated peripherally as a nuisance parameter. The outstanding accuracy of Swarm magnetic field data and increasing demand for fast-track magnetic field products has pushed the frontier of the field to a point where sophisticated core and external magnetic field models are hindered by improper modelling of induced fields. We propose a versatile and efficient way of modelling induced fields in ground and satellite measurements, which also enables modelling in near real-time settings as is required by many present Space Weather products. The proposed approach also offers a more consistent way to assimilate geomagnetic data from ground observatories and satellites into physics-based magnetic field models.