Electromagnetic methods for studying the Earth, electromagnetic techniques of geophysical prospecting, in particular, are conventionally based on the fact that any electromagnetic field, either observed on the Earth or artificially excited by generators, satisfy Maxwell's equations and is analytically described by these equations.
This opinion is so popular among geophysicists that any minor deviation from the corollaries following Maxwell's equations is considered to be absent in nature. As an example we can mention a non-potential magnetic field in the practically non-conducting Earth's atmosphere, which is excited by temporal magnetic variations of a natural electromagnetic field; an electric field, vertically directed towards the Earth's surface with almost fully absent vertical currents in the atmosphere; the presence of a toroidal magnetic field in the atmosphere also with almost absent the conductivity current through the atmosphere; the presence of ineradicable and sufficiently large errors in the data interpretation in MTZ and ZCB.
In this case, it would appear reasonable to assume that in nature to be exact in its part that generates electromagnetic fields with the sources on the spherical surfaces in the ionosphere or in the Earth's spherical layers, as an example, there could exist an electromagnetic field (not contained in Maxwell's equations!) that is certainly present in experimental data but are not analytically described by Maxwell's equations.
Poloidal and toroidal magnetic fields have been known since the time of Lamb, Love, Backus and others. In these publications, a magnetic field consists of the two parts – toroidal and poloidal magnetic fields.