Deriving secular variation from CHAMP satellite magnetic field measurements

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The geomagnetic field varies on time scales from years to hundreds of millions of years. In this application we focus on the short-period end of the time scale. Results obtained in this period range can be used to investigate core/mantle coupling and inhomogeneities in mantle conductivity. A low flying satellite is a very powerful tool for determining the space/time distribution of sub-decadal secular variation. We are now at the beginning of a series of space missions dedicated to the study of the geomagnetic field. One major contribution to this initiative is expected from the German satellite CHAMP, scheduled for launch 15th July 2000 and designed for an active life of 5 years. Since satellites measure the sum of all internal and external field contributions, a proper separation of these parts is a prerequisite for a reliable detection of main field secular variation. In this proposal we plan to model the internal and external part of the magnetic field simultaneously by making use of all known constraints posed by the physical properties of the various field sources. Without significant progress in this field the markedly improved resolution of the new missions cannot be utilised for deriving better secular variation data.