The Extremely Low Frequency band (ELF: 0.03 – 1000 Hz) electromagnetic signals from thunderstorm lightning discharges can propagate around the globe in the Earth-ionosphere resonance cavity and thus be used for ionosphere monitoring. We use ELF observations of the World Wide Lightning Location Network (WWLLN) impulses to examine ELF propagation velocity and arrival azimuth under diurnal changes in two days of September 20th and 21st, 2023. Also temporary effects of solar flares’ ionizing fluxes are monitored, leading to increasing the ELF signal propagation speed modulated by the X-ray flux intensity. We present for the first time a simple method for automatic and large-scale analysis, utilizing data from two registration systems (ELF and WWLLN) and enabling easy evaluation of changes in wave propagation speed. The compared samples of WWLLN impulses generated in selected azimuth and distance sectors for Africa and America reveal varying effects of signal refraction, with increased azimuth changes for signals propagating across the ionospheric ionization gradients. The method has a potential to become a standard tool for the analysis and monitoring of the lower layers of the ionosphere.