Generation of electromagnetic signals at combination frequencies in the ionosphere

Artificial ionospheric source of low-frequency electromagnetic fields in the problems of environment sounding

“…For correct estimation, the replacement P → P i , where P i is the part of power absorbed at the lower boundary of the ionosphere in the region with vertical size of the order of the skin-layer thickness, should be performed in Eq. (2). It should be mentioned that the notion of a skin layer in the ionosphere, which is used here and was used before [2], is conventional since there is no full analogy between the Earth and the ionosphere.…”

“…This situation is similar to an ionospheric source for which the distributed ionospheric current from the viewpoint of ground-based observation can be replaced by an equivalent source located at the lower edge of the ionosphere. In the case h δ i , where h is the height of the lower edge of the ionosphere and δ i is the skin layer in the ionosphere, the equivalent source is also a magnetic dipole with moment (1), whose parameters have the ionospheric values [2]. Therefore, for estimation of the efficiency of an ionospheric source in problems of the Earth electromagnetic sounding, it is expedient to compare the magnetic moments of the ionospheric source and the ground-based source using the galvanic excitation technique for reasonable parameters of the setups and comparable power expenditures.…”

“…For the optimal conditions, the total current moment of an ionospheric source of low-frequency fields is yielded by the universal formula [2] (…”

“…Later (in 1985), reliable recording of CFSs was reached in the extremely low-frequency range (ELF, 3-30 Hz) using the "Sura" facility. The results of the "Sura"-based studies of CFSs, including the first tests on ionosphere diagnostics, are described in detail in [2]. The CFS generation mechanism based on the modulation of natural ionospheric current systems is developed in detail [2] and is generally accepted at present.…”

“…The results of the "Sura"-based studies of CFSs, including the first tests on ionosphere diagnostics, are described in detail in [2]. The CFS generation mechanism based on the modulation of natural ionospheric current systems is developed in detail [2] and is generally accepted at present. From the viewpoint of priority, we note that the modulation mechanism of the electron number density and, correspondingly, ionospheric currents as the sources of low-frequency electromagnetic fields was proposed for the first time in paper [3], in which the effect of periodic heating of the lower ionosphere was considered the reason for modulation of the electron number density and, correspondingly, ionospheric currents due to the temperature dependence of the rates of photo-chemical reactions (the number-density source).…”