Present-day Geomagnetic Field
It is a general consensus that the present-day geomagnetic field is a typical picture of the past geomagnetic field. As easily seen from the magnetic charts for the year 2025 (IGRF-14), the field is well approximated by a dipole field which is a field produced by a magnetic dipole, or an imaginary bar-magnet at the center of the earth.
General dipole nature of the geomagnetic field justifies to study the past geomagnetic field in terms of a virtual dipole moment. Virtual dipole moment (VDM) is a dipole moment calculated from the geomagnetic field observed at a point on the globe supposing that the field is entirely a dipole field. The next image shows that the dynamic range of the VDM distribution (7.9±1.5×1022 Am2, standard deviation is 19% of the mean) is reduced from that of the distribution of the total force (42±11 μT, standard deviation of 26%), showing the dipole nature of the geomagnetic field (93% of the total power spectrum).
