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 2020, 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. This image shows that the dynamic range of the VDM distribution (standard deviation is 16% of the mean) is much reduced from that of the distribution of the total force (25% of the mean), showing the dipole nature of the geomagnetic field (90% of the total power spectrum).
