## 1 Introduction
The average radon flux density for the entire ocean is equal to 0.0382 mBq m\({}^{-2}\) s\({}^{-1}\)[14] and is much smaller than the typical estimates for the average flux density from land, which is in the approximate range of 20 to 35 mBq m\({}^{-2}\) s\({}^{-1}\)[15]. Overland, the radon concentration depends on the tectonic conditions. For example, in Mysore city (India), it is of order 20 Bq/m\({}^{3}\)[16]; simultaneously, in the vicinity of active faults, radon concentration may reach 2000 kBq/m\({}^{3}\), five orders of magnitude larger [17]. Thus, Radon emanation from an area of earthquake preparation (active faults) may increase the conductivity and decrease the resistance of the surface-layer air (the lower tropospheric part of the GEC). A decrease in boundary layer resistance reduces the total ground-ionosphere electrical resistance. This, in turn, increases the vertical fair-weather current in the GEC and lowers the ionosphere (to maintain the continuity of the electron flow). Hence, the effects of earthquake preparation modify the ionosphere parameters. The concept of the GEC was successfully used in [18; 19] to explain the results from the DEMETER satellite observations [20], which showed a statistically significant decrease in the natural VLF (~1.7 kHz) wave intensity related to 8400 nighttime earthquakes of M \(\geq\) 5.0 within 440 km of the epicenters. In [21; 22], a modified configuration of the GEC is discussed. Its external element is located on the magnetopause with the electromotive force generator driven by solar wind energy; its internal element is in the solid Earth, with the electromotive force generator driven by the tectonic processes [22]. The modified GEC may be considered a mediator in transmitting solar wind energy into the Earth's crust. The functioning of a GEC will depend on electrical conductivity along the entire path from the magnetopause to the Earth's crust. It is mentioned above that in the near-ground troposphere, ionization may be produced by the isotopes of radon [14; 15; 16; 17], whose emanation is expected to be strong at overactive faults. In the upper troposphere and lower stratosphere, the galactic cosmic rays influence the ionization and, therefore, the electrical parameters of the atmosphere [23; 24]. Cosmic rays are energetic particles (primarily protons and \(\alpha\)-particles), which, according to their origin, are categorized as either galactic cosmic rays (GCRs) or solar cosmic rays (solar energetic particles, SEPs) [23]. GCRs are always present in the Earth's vicinity, while SEPs occur sporadically, usually in conjunction with the Sun's giant eruptive events (solar flares or coronal mass ejections). The energy inputted by cosmic rays in the Earth's atmosphere is about \(10^{-9}\) times that of solar energy [25]. However, cosmic rays are the only source of ion production in the lower stratosphere and upper troposphere [23; 24]. The cosmic rays are inputted to the electrical properties of the atmosphere and the global electric circuit by manipulating atmospheric conductivity, vertical electric current, and vertical ionospheric potential gradients. It is shown in [26; 27] that changes in the surface potential and ionospheric potential gradients correlate well with changes in GCR. About 95% of cosmic ray particles have an energy of 0.1-15 GeV, which contains more than 60% of all cosmic ray particle energy [28; 29]. The cosmic ray particles with energy \(\leq\)15 GeV undergo an 11-year modulation, and the flux of cosmic ray particles with this energy may decrease more than twofold when the solar activity period changes from the minimum to the maximum [28]. Thus, the effect of cosmic ray ionization in the lower stratosphere and upper troposphere should be more dominant during the period of minimum solar activity.