1. Helmholtz Centre Potsdam-GFZ German Research Centre for Geosciences, Section 2.3 Earth's magnetic field; Potsdam Germany
2. Equipe de géomagnétisme, Institut de Physique du Globe de Paris; Paris France
3. Department of Planetary Physics; Institute of Planetary Research, German Aerospace Center; Berlin Germany
4. UC Berkeley Space Sciences Laboratory; Oakland CA USA