Solar flares effects in amplitude and phase variations of VLF radio station signals during September 2017

Amplitude and phase variations of radio signals (11.9 kHz) of Khabarovsk and Krasnodar transmitters registered in Yakutsk and Tiksi during solar flares activity on September 04 - 10, 2017 are considered. The solar flares effects determined in a VLF signal phase delay during daytime propagation. The magnetic storm appeared on September 8 in amplitude and phase variations of VLF signals recorded in Yakutsk. The Khabarovsk signal amplitude decreased by 8 dB on September 8 (nighttime propagation). The phase delay of Krasnodar signal decreased by 70 degrees on September 8 (nighttime propagation) and by 40 degrees (daytime propagation) on September 9. For Khabarovsk - Tiksi propagation path the signal phase delay reduced by 35 degrees and the attenuation increased by 3.5 dB (19:40 UT) on September 10, 2017. For Krasnodar - Tiksi propagation path the signal phase delay decreased by 40 degrees (17-18 UT) on September 10, 2017. For Khabarovsk - Yakutsk VLF signal propagation path there is a phase delay decreasing by 6 degrees (daytime conditions: from 21 UT September 10 till 06UT September 11, 2017). According to the receiver in Yakutsk the phase delay of the Krasnodar signal decreased by 60 degrees on September 10 for a nighttime (17-18 UT) and the phase delay decreased by 50 degrees for daytime conditions on September 11. There is an attenuation increase of the Krasnodar signal on September 10 (from 17-18 UT). Such circumstances are caused by a sharp increase in the flux of high-energy solar protons on September 10-11.