Magnetic field measurements taken on ground or in space by satellites contain contributions from various sources: in the core and crust, as well as from ionospheric and magnetospheric current systems plus their induced counterpart in the Earth's interior. The proper separation of these sources, all of which have specific space-time structure, is a very challenging tasks.

The objective of the session is to bring together scientists from the different communities to present their data and results on external current systems, the main field, induction studies and crustal fields.

We solicit contributions related to the various magnetic field sources and their separation. Contributions on the synthesis of ground data (in particular magnetic observatories) with satellite data are particularly welcome. Applications of data and modelling to the
interpretation of the Earth system are also strongly encouraged.