GNSS derived total electron content variation along the annularity path associated with O/N2 ratio change during the annular solar eclipse of 21 June 2020

The present work focused on the low latitude ionospheric perturbation during the 21 June 2020 annular solar eclipse. The study is performed by using Global Navigation Satellite System (GNSS) derived total electron content (TEC) data from GNSS sites located across the annularity path. The annularity path was divided into four major regions: Africa, Arab, India and Taiwan, corresponding to morning, afternoon and evening local time. The GNSS sites are lying nearly the same eclipse magnitude/obscuration chosen for TEC analysis with two PRNs 06 & 19. The most remarkable finding is the presence of pre-eclipse enhancement in the TEC over the Indian region. The average change in TEC varies as ∼3.0-0.5 TECu (Total Electron Content Unit) during the morning (at Africa & Arab sites), ∼2.8 TECu during the afternoon (at Indian sites), and ∼3.5 TECu during the evening (at Taiwan sites). TEC derived from the COSMIC-2 satellite and global ionospheric maps (GIM) showed a maximum decrease in the evening and morning, while it was a minimum during the afternoon. The O/N₂ ratio from the GUVI payload onboard the TIMED satellite shows a significant increase of ∼12% on the eclipse day over the Indian region. Such thermosphere composition changes are suggested to be induced due to eclipse associated temperature change over the Tibetan plateau, which brought N₂ down and increased O/N₂ ratio, particularly over the Indian region. The enhanced O/N₂ ratio, in turn, enhances ionospheric electron density, thus explaining the pre-eclipse effect and minimum electron density change over the Indian region.