Impact of Three Solar Eclipses of 2019-2020 on the D-Region Ionosphere Observed From a Subtropical Low-Latitude VLF Radio Station

Ionospheric impact of three solar eclipses (January 2019, December 2019, and June 2020) observed by Very Low Frequency (VLF) radio signals from a single receiver at a subtropical low-latitude station in India is presented here. Perturbations in signal amplitudes of VLF transmitters such as the VTX (18.2 kHz), NWC (19.8 kHz), JJI (22.2 kHz), and DHO (23.4 kHz) are analyzed. Both positive, negative, and also mixed-type of amplitude deviations are observed which are explained based on the solar eclipse obscuration profiles over the entire propagation paths. The difference in observed amplitude deviations for a VLF signal during the different solar eclipses are reproduced using the Long Wave Propagation Capability code and solar obscuration profile. Particularly, the effects of two solar eclipses on the VLF signal propagation characteristics have been analyzed. The modal attenuation coefficients of the VTX signal in the earth-ionosphere waveguide are decreased with the increase of solar obscuration. A negative linear relationship of VLF signal attenuation with solar obscuration has been found for the first time during the solar eclipse. The relations are almost similar for the two solar eclipses of December 2019 and June 2020. Further, the percentage reduction of the D-region electron density profiles as a function of altitude and solar obscuration during the two solar eclipses is presented.