Geomagnetic reversal

Builds on Earth's magnetic field Dipole model of the Earth's magnetic field

Definition

Expand the internal part of the Earth's magnetic field in spherical harmonics with Gauss coefficients $g_n^m, h_n^m$ . The coefficient $g_1^0$ is the axial dipole coefficient, the strength of the dipole aligned with the rotation axis. The polarity of the field at a time is normal if the average of $g_1^0$ over a few thousand years is negative. It is reversed if this average is positive. A geomagnetic reversal is a transition from one polarity to the other. After it, the new polarity persists for a time long compared with the transition.

Remarks

Example: the Brunhes–Matuyama reversal, about 780,000 years ago, took the field from reversed polarity to the present normal polarity, and normal polarity has persisted since then. Non-example: a geomagnetic excursion is a large swing of the field direction that returns to the original polarity within a short time; it fails the persistence clause. With $g_1^0 < 0$ , the dipole points to the geographic south, so field lines leave the southern hemisphere and a compass needle points north. The sequence of polarity intervals through time is the geomagnetic polarity time scale.

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Dipole model of the Earth's magnetic field concept
Earth's magnetic field concept
Geomagnetic reversal definition

Tag	`KPMMHCZEWH`
URI	`m2://KPMMHCZEWH`
Kind	definition
Writing	W0 stub
MSC	86A25
Defines	Geomagnetic reversal
Uses	Earth's magnetic field, Dipole model of the Earth's magnetic field
Changed	3 November 2026

Geomagnetic reversal

Definition

Remarks

Reading path

Further reading

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