Nils Olsen

The 2025 Petrus Peregrinus Medal is awarded to Nils Olsen for leadership in the field of continuous satellite geomagnetometry and analysis that has profoundly advanced our understanding of magnetic processes in Earth’s interior, ocean and space environments.

Nils Olsen shepherded into existence our current epoch of continual satellite measurement of the geomagnetic field. In doing so, his efforts have revolutionised our measurements of Earth’s field as well as our interpretations of magnetic induction processes occurring above Earth, in our oceans, in the lithosphere, mantle and core.

Olsen started working on electromagnetic sounding of the crust and mantle, using Earthbound observatory data to determine the electrical conductivity structure down to 1000 km into the mantle. His detailed analyses also quantified the magnetic inductive signals produced by tidal flows in ocean. He went on to develop comprehensive models of the geomagnetic field that include signals due to the core, lithosphere, ocean tides, ionosphere and magnetosphere.

Olsen has also led the development of the CHAOS magnetic field models, based originally on CHAMP and Orsted satellite mission data. These were the first models to include maps of the first time derivative of the field, which have higher spatial resolution than that of the 'static' field itself. This breakthrough was made possible by the insight that the lithospheric signal, which swamps the static field at higher spatial wavenumbers, is essentially absent in the time-derivative data. The latest CHAOS models now contain over twenty years of data, including that from the Swarm mission. The strong temporal variations in the CHAOS models have redefined our understanding of the dynamics of Earth’s core. CHAOS-based core flow inversions have revealed the existence of rapid wave motions, geomagnetic jerks, time-varying polar jet flows, and hemispherical scale gyres.

Key to all these scientific discoveries has been Olsen’s international leadership in geomagnetic satellite missions. His care in mission planning, in the development of novel in-flight magnetometer calibration methods, and in generating the leading representations for the various field sources underlies the community’s success in global geomagnetic field modelling over the past two decades.

Both for his breadth of scientific contributions and for the depth of his efforts to generate continual global geomagnetic data sets, the Petrus Peregrinus medal is most deservedly awarded to Nils Olsen.