Analysis of the propagation conditions of radio waves add-ons in the Earth-ionosphere waveguide on the Novosibirsk–Ulan-Ude and Komsomolsk-on-Amur–Ulan-Ude routes during magnetic storms and solar flares August 31–September 12, 2017

An analysis of the amplitude and additional phase $\varphi_{\text{add}}$ of the additional field of the VLF ADN RNS RSDN-20 field during strong magnetic storms and solar flares from September 1–12, 2017 was carried out. Paths of the latitudinal strike were inves-tigated: 1 “Novosibirsk–Ulan-Ude”, length — 1580 km; 2 “Komsomolsk-on-Amur–Ulan-Ude”, length — 2080 km. Daily variations of the median amplitude of radio signals of 11.9 and 14.88 kHz on tracks 1 and 2, obtained after decimation and transmission of the measurement array through the digital smoothing polynomial Savitsky–Golay filter, are considered. The field calculations in the Earth-ionosphere waveguide are presented. Analysis of the propagation conditions of radio waves during magnetic storms and solar flares revealed significant differences in the spatial amplitude-phase phenomena in normal and anomalous geomagnetic conditions at frequencies of 11.9 and 14.88 kHz when propagating along spatially separated paths of latitudinal strike. The main factor influencing the parameters of the VLF signal in the Earth-ionosphere waveguide during heliogeophysical disturbances is the increase in the electron concentration in the $D$ layer of the ionosphere and the associated change in the waveguide geometry.