Sensing the Earth's low ionosphere during solar flares, using VLF signals and GOES solar X-ray data

Simultaneous analysis of the effects of M2.5-class solar flare event on VLF signal amplitude and phase delay variations for the GQD/22.1 kHz and NAA/24.0 kHz signal traces was carried out. Solar flare data were taken from GOES12 satellite one-minute listings. The VLF data recordings were performed at the Institute of Physics, Belgrade, Serbia, by the AbsPAL system. It was found that a single solar flare event changes the lower ionosphere electron density height profile, in dependence of the Earth-ionosphere waveguide characteristics. The values of the parameters sharpness and reflection height during flare conditions have been evaluated for two traces considered.