Natural Variations of the Geomagnetic Field: Observations and Application to Study of the Earth’s Interior and Ionosphere

The magnetic investigations carried out incessantly from the very moment the Institute of Geophysics was established in 1953 are outlined. Since that time, continuous observations of the natural magnetic field of the Earth, also called “magnetic service”, have been carried out. The research methods are discussed, which cover a wide scope of problems relating to the use of natural electromagnetic field variations, including the recognition of the Earth’s crust and upper mantle, search for electromagnetic earthquake precursors, and the ionosphere state monitoring via surface-based observations of the magnetic field. The reported investigations are of methodological nature, relating to recording and processing of data, as well as geophysical and geological modeling and interpretation. The major results obtained during 60-year activity, referring to the structure of the Earth’s crust and mantle in central Europe, are summarized.