Jordens magnetfelt

Division of Geomagnetism

The Division of Geomagnetism uses magnetic field measurements from satellites and ground stations to explore the Earth.

The magnetic field provides valuable knowledge about Earth's interior, because its slow variations reflect movements of the material in the core, rapid field changes depend on the electrical conductivity of the upper mantle, and because small wavelengths features can be used to map crustal structures. The magnetic field can also be used to explore the upper atmosphere (ionosphere and magnetosphere) and its connection with processes on the Sun.

The division’s activities primarily focus on:

  • measuring Earth's magnetic field
  • investigating the underlying physical processes producing the field and its variations
  • developing methods to separate the different contributions from the core, crust and the Earth's upper atmosphere (ionosphere and magnetosphere)
  • developing and calibrating instruments to measure the Earth's magnetic field, which are used in observatories around the world.

Main research area: Earth's magnetic field 

The Earth's magnetic field originates from three main sources, all of which are the subject of research at the National Space Institute. The dominant component is the so-called 'main' or 'core' field, generated by a liquid metal dynamo operating in the Earth's fluid outer core. The second contribution comes from the Earth's lithosphere, from magnetised rocks, of typical magnitude hundreds of nT. Core and crustal fields together are denoted as 'internal' fields since their sources are within the Earth.

'External' fields are due to electric currents in the ionosphere and magnetosphere caused by the interaction of the Earth’s main field with the sun. Finally, the time varying external fields produce secondary, induced currents in the Earth’s interior, which in turn cause a secondary, induced, magnetic field. 

The largest part of the magnetic field at the Earth's surface comes from sources internal to the Earth. By assuming that this field is a potential field, it is possible to construct maps of the spatial structure of the surface magnetic field (wavelengths greater than order 1000 km), for a specific time (epoch). 

Unfortunately, potential theory tells us that formally we can say little more about the origin of the field within Earth – whether it originates in the core, mantle of the crust. All we can say for sure is that it originates within the Earth, but where in the Earth cannot be distinguished. However, by looking at the structure of the field – and making assumptions about its sources – we are able to make further inferences. The large-scale part of the field (wavelengths greater than 3000 km) is dominated by sources in the Earth’s core, while the small-scale part is dominated by sources in the crust. 

Using data collected by satellites (like Ørsted, CHAMP and SAC-C) and by ground observatories, the Division of Geomagnetism at the National Space Institute determines models of the present Earth magnetic field and its temporal change.

Contact

Nils Olsen
Professor -head of Geomagnetism
DTU Space
+45 45 25 97 08

Contact

Chris Finlay
Senior scientist
DTU Space
+45 45 25 97 13