The Westward Drift of the Earth's Magnetic Field in Historic Times

Old records of magnetic measurements and archeomagnetic data at various places were collected to examine whether the westward drift has been a persisting feature of the earth's magnetic field and to investigate the extent to which drifting of the field has contributed to the observed secular variation. It turned out that main features of the secular variation such as maxima and minima of magnetic declination and inclination; were very likely to have drifted westwards with a velocity of about 0.36°/year over several hundred years. Comparison of the observed time variation with the spatial distribution of the present geomagnetic field suggests that the westward drift of the non-dipole field is responsible for producing a large part of the secular variation, even for such long period as 1000 years.