Core (Main) Magnetic Field

97 -99% of the Magnetic Field  at the Earth's surface  is  produced by electric currents  driven by a self-sustaining dynamo process in the  Earth's conducting liquid outer core. That portion of the geomagnetic field generated in the Earth's core is referred to as the Core (Main) magnetic field simply because it is the largest contributor to the total geomagnetic field. It ranges in magnitude between 20,000 nanoTeslas (nT) at the geomagnetic equator and about 65,000 nT at the poles.

sketch of main magnetic field

The present field is close to that expected from a geocentric dipole inclined  at about 11 to the Earth's rotational axis

dipole magnetic field

The Main field varies slowly but erratically in time, as illustrated in the following figure  (Olsen et al., 2000)

Main Magnetic Field


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