Regional modeling of the geomagnetic field in Europe from 6000 to 1000 B.C.

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Abstract

We have developed a first low-degree regional geomagnetic model for the European continent valid for the period 6000–1000 B.C. from a selected compilation of sedimentary and archeomagnetic data (the SCHA.DIF.8K model). This model provides information about both direction (declination and inclination) and intensity of the Earth's magnetic field. By connecting it with our previous model, SCHA.DIF.3K, valid from 1000 B.C. to 1900 A.D., and the IGRF, we furnish continuous geomagnetic field information for the last 8000 years in Europe. It has been developed using the Revised Spherical Cap Harmonic Analysis in 2 Dimensions technique (R-SCHA2D) and using the norm of the Earth's magnetic field to constrain the inversion problem. The size of the cap is 22°, and the maximum degree of the expansion is 2. The linearization problem was solved by using the truncated Taylor's series applied to the expressions representing the relationship between the declination, inclination, and intensity data and the Cartesian components of the geomagnetic field. We used the geocentric axial dipole (GAD) field as our initial or reference field. For time, we used the classical sliding overlapping window method. The size of the window was set to 100 years shifted by 50 years. We compared the model's prediction with the input data, with the global CALS7K.2 model, and with new independent data. The regional model shows a better fit to the input and to the independent data than the global model, especially in terms of intensity, and agrees with the virtual axial dipole moment given by other studies. For the last 8000 years, the European geomagnetic field has recorded rapid changes or archeomagnetic jerks. The average field for the last 8000 years in Europe is indistinguishable from the GAD field.

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