Dipole representation of the earth's magnetic field
De Meyer, F.
Earth and related Environmental sciences
earth's magnetic field
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Magnetic dipoles are used as a first approximation to the electric currents in the Earth’s core that are assumed to reproduce the main magnetic field. This model is restricted to eccentric radial dipoles at equal distances from the center of the Earth. A non-linear least squares procedure is used to adjust the longitude, latitude, and dipole moment of the dipole for a best fit to the field components of the International Geomagnetic Reference Field (IGFR) on the surface. Updated IGRF models are designated Definitive Geomagnetic Reference Fields (DGRFs). For the DGRF 1965 (10th degree and order) the position of 34 dipoles at the core-mantle interface was initially determined from the current function. Progressively better fits were obtained as the dipoles were placed deeper and six of the dipole sources were eliminated as greater depths. The 85-parameter, 28-dipole model, with the radial dipole at a distance of 0.27 Earth radii from the geo center produced nearly as good a fit to the 1965 DGRF as the 120 spherical harmonic coefficients. The great depth of the radial dipoles is qualitatively explained by the shielding effect from currents In the dipole model gives a very good fit to the original field. During the 1900-2000 period a mean westward drift of 0.07 deg./year is obtained and the field clearly has both drifting and standing parts. Variations of the secular drift with latitude indicate that the core does not rotate uniformly as a rigid body. The irregular small-scale behavior of the DGRF 1945 and DGRF 1950 is confirmed.
CitationDe Meyer, F. (2002). Dipole representation of the earth's magnetic field. , Vol. 22, Issue Publication scientifique et technique n° - Wetenschappelijke en technische publicatie nr., IRM,