Dictionary:Normal magnetic field
1. A smooth component of the Earth’s magnetic field that is free of anomalies of exploration interest. Ordinarily computed from a low-order spherical harmonic expansion constrained by satellite measurements. The normal field of the Earth varies slowly with time. Often identified with the International geomagnetic reference field (q.v.). 2. The magnetic field of the Earth (q.v.) during an epoch when it is roughly aligned with the present-day field. Antonym: reversed magnetic field.