Geomagnetic secular variation

Geomagnetic secular variation refers to changes in the Earth's magnetic field on time scales of about a year or more.

[1] The geomagnetic field changes on time scales from milliseconds to millions of years.

[1] In most models, the secular variation is the amortized time derivative of the magnetic field

Over such a time scale, magnetic declination is observed to vary over tens of degrees.

[5] A prominent feature in the non-dipolar part of the secular variation is a westward drift at a rate of about 0.2 degrees per year.

[6] Changes that predate magnetic observatories are recorded in archaeological and geological materials.

Estimated declination contours by year, 1590 to 1990 (click to see variation).
Strength of the axial dipole component of Earth's magnetic field from 1600 to 2020, according to three models.