ИСТИНА

In this study, we develop a theoretical model [1] of the effect of X-ray radiation from a solar flare (SF) on the properties of the lower ionosphere and the Earth-ionosphere waveguide. In our model, we investigate the time dependences of ionospheric parameters during X-ray radiation, in contrast to the model [1], which deals with ionospheric parameters averaged over the time of SF. A flat flux of time-varying X-ray radiation incident on the ionosphere is considered. The interaction of this radiation with the ionosphere leads to the ionization of air molecules and the production of free electrons. The photons in the incident flux is assumed to be distributed in their energy according to Planck's law. The time dependence of the radiation temperature is estimated using data from a two-channel X-ray sensor on board the GOES satellites. The photon energy absorption coefficient is assumed to depend on the photon energies and air density. In this approach, the ionization rate is calculated as a function of altitude and time. Changes in the number densities of electrons and ions are described by a set of differential equations, which take into account the rates of production and recombination of particles. The solution of these equations is used to calculate changes in ionospheric conductivity which affect the properties of the upper wall of the Earth-ionosphere waveguide. The theory was applied to study the relationship between the intensity of X-ray radiation and the change in the weighted average frequency of Schumann resonances (SRs), which was observed for a number of SFs of various classes. The frequency shifts of the SRs were calculated for 80 SFs observed between 2002 and 2017. The time series recorded by on-board X-ray sensors on the GOES satellites were used as the initial data. The results of our calculations are in good agreement with the experimental data [2]. The study is supported by the grant 25-27-00539 from the Russian Science Foundation. References 1. Surkov V.V. The effect of X-ray radiation from a solar flare on the frequencies of Schumann resonances // J. Atmos. Solar-Terr. Phys. 2025. V. 271. 106537. https://doi.org/10.1016/j.jastp.2025.106537. 2. Shvets A.V., Nickolaenko A.P., Chebrov V.N., 2017. Effect of solar flare on the Schuman-resonance frequency // Radiophys. Quantum Electron. 2017. V. 60(3). P. 186–199. https://doi.org/10.1007/s11141-017-9789-8.