The main part of the geomagnetic field arises from electric currents in the Earth’s outer core. It extends to a distance of ∼10 Earth radii and acts as a shield for protecting our atmosphere against solar and cosmic particle radiation. It also determines the strength and geometry of ionospheric and magnetospheric current systems. While the Earth’s core field varies on time scales of months to years, electric currents in the ionosphere and magnetosphere change within seconds to days, e.g., during space weather events. Continuous monitoring of the various magnetic field variations is thus important to characterize the Earth’s space environment and ensure the preparedness of modern technology on the ground and in space on which society increasingly depends.
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