Planetary scale geomagnetic secular variation foci in the last 400 years

The Earth's surface magnetic field and its secular variation (SV) are composed of several constituents, at sub-centennial (60-90 years) and inter-decadal (20-30 years) timescales, of internal origin, and at decadal (similar to 11 years) timescale, of external origin, superimposed on a so-called inter-centennial constituent (timescale of about 400 years or larger). In this study we explore the appearance, structure, and dynamics of the SV foci from the perspective of the constituents with internal sources. Data from long time-span geomagnetic models, such as gufm1 (1590-1990) and COV-OBS (1840-2010), have been used to separate various constituents by Hodrick-Prescott (HP) and Butterworth filtering. Time-Longitude/Latitude plots, based on main field models time series on a grid of 2.5 degrees x2.5 degrees were constructed for various longitudes/latitudes respectively, on which a Radon transform was applied to get information on displacement in time of the constituents and of the SV foci, in the form of Latitude-Azimuthal-Speed and Longitude-Meridional-Speed power plots. The Earths surface field variability for the 400 years time-span is analyzed for the constituents of the field. Assessment of the geomagnetic field evolution at the Earth's surface and its characteristics, by our approach, revealed: (1) tendency of the westward drift of the inter-centennial constituent to the southern hemisphere, (2) absent meridional displacement of the inter-centennial constituent, (3) westward drift of the higher frequency constituents in a +/- 20 degrees equatorial band.

Automated summary

This study examined the Earth's surface magnetic field and its secular variation, focusing on the internal constituents and dynamics of the SV foci. By analyzing long time-span geomagnetic models and applying filtering techniques, the study revealed new features of the Earth's surface field evolution, such as the westward drift of the inter-centennial constituent and the westward drift of higher frequency constituents in the equatorial band.