Extending comprehensive models of the Earth's magnetic field with Ørsted and CHAMP data

Abstract

SUMMARY A new model of the quiet-time, near-Earth magnetic field has been derived using a comprehensive approach, which includes not only POGO and Magsat satellite data, but also data from the Orsted and CHAMP satellites. The resulting model shows great improvement over its predecessors in terms of completeness of sources, time span and noise reduction in parameters. With its well separated fields and extended time domain of 1960 to mid-2002, the model is able to detect the known sequence of geomagnetic jerks within this frame and gives evidence for an event of interest around 1997. Because all sources are coestimated in a comprehensive approach, intriguing north–south features typically filtered out with other methods are being discovered in the lithospheric representation of the model, such as the S Atlantic spreading ridge and Andean subduction zone lineations. In addition, this lithospheric field exhibits significantly less noise than previous models as a result of improved data selection. The F-region currents, through which the satellites pass, are now treated as lying within meridional planes, as opposed to being purely radial. Results are consistent with those found previously for Magsat, but an analysis at Orsted altitude shows exciting evidence that the meridional currents associated with the equatorial electrojet likely close beneath the satellite. Besides the model, a new analysis technique has been developed to infer the portion of a model parameter state resolved by a particular data subset. This has proven very useful in diagnosing the cause of peculiar artefacts in the Magsat vector data, which seem to suggest the presence of a small misalignment bias in the vector magnetometer.