Westward drift in the secular variation of the main geomagnetic field derived from IGRF models
De Meyer, F.
Earth and related Environmental sciences
International Geomagnetic Reference Field
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The eight generation of the International Geomagnetic Reference Field (IGRF) is used to investigate the westward drift in the Secular Variation (SV) of the Main Geomagnetic (MG) field for the period 1900-2000. The drift is estimated by tracing the position of the maximum of the cross-correlation function of isoporic maps for different epochs, a procedure known as Briggs’method I. The magnetic potential V associated with the SV-field exhibits a rather simple spatial distribution and steady variation tendency on the Earth’s surface. The average westward drift velocity of about 0.36°yr-1 obtained from the SV-potential is fairly grater than the westward drift rate of nearly 0.15°yr-1 of the MG-field itself for the same period. The vertical component (Z) and east component (Y) of the SV-field show complex patterns, from which the average rate of westward drift is estimated as 0.35°yr -1 . The spatial distribution of the north component (X) displays an even more intricate structure with several small-scale vertices, especially for the period 1945-1955, giving a scarcely smaller overall westward drift velocity of 0.33°yr-1. The irregular behaviours of the high-degree Gauss coefficients in the IGRF 1945, 1950 and 1955 only slightly affect the spatial design of the magnetic potential, but they highly distort the distribution of the magnetic components. The ~80-yr periodicity observed in the secular variation is compatible with strong-field dynamo models of the &ώ type.
CitationDe Meyer, F. (2005). Westward drift in the secular variation of the main geomagnetic field derived from IGRF models. , Vol. 38, Issue Publication scientifique et technique n° - Wetenschappelijke en technische publicatie nr., IRM,