Geomagnetic Secular Variation: Theory
A major part of the geomagnetic field is considered as being generated through hydromagnetic processes in the Earth's liquid core, which consists mostly of iron. Since the electrical conductivity of iron is high, electric currents are induced in the core by motions of the liquid iron in the presence of the magnetic field. The electric currents induced in this way recreate the magnetic field. Accordingly, time variation in the geomagnetic field is regarded as a manifestation of the fluid motions in the core, and the geomagnetic secular variations are understood within a frame of the generation process of the geomagnetic field dynamo process (see Geomagnetic Field, Main: Theory ).
There is yet no unanimous agreement regarding the dynamo process of maintaining the geomagnetic dipole field. Some require intense toroidal fields (the field confined within the core without the radial component) more than ten times stronger than the poloidal fields (the