A Method for Determining a Generalized Representation of Geomagnetic Field Sources

Abstract

Summary A new method for modelling a geomagnetic field has been developed. After the directional data has been analysed in terms of spherical harmonics, a representation of the field sources is obtained as a combination of a geocentric axial dipole and an eccentric (not necessarily axial) dipole. The free parameters are the location of the eccentric dipole and the relative proportions of the field arising from the geocentric axial dipole and from the eccentric dipole. Previous models for field source configurations are included as special cases. The new method has the particular advantage that it emphasizes the choice among models rather than the fit to a pre-selected model. Analyses of synthetic data sets demonstrate the stability and accuracy of the method. A regionally-averaged set of late Cenozoic palaeomagnetic data can be best represented by a combination of 75-80 per cent geocentric dipole and 25-20 per cent eccentric dipole. The eccentric component of this configuration is displaced toward the North Pacific.