Occurrence of Nighttime Irregularities and Their Scale Evolution in the Ionosphere Due To the Solar Eclipse Over East Asia on 21 June 2020

Solar eclipse is a daytime phenomenon that significantly disturbs the ionosphere, but whether the eclipse induces ionospheric irregularities in the nighttime remains unknown. In this study, we analyzed the dense total electron content (TEC) observations from the ground-based Global Navigation Satellite System receivers over East and South Asia to examine the development of the irregularities in the nighttime on the day of the 21 June 2020 annular solar eclipse. The rate of TEC index (period <5 min) indicates the occurrence of the irregularities that evolve from the large or coarse structures with a period ranging from hours to dozens of minutes in the nighttime due to the eclipse. We take advantage of the data-adaptive analysis method, Hilbert-Huang transform, to derive the instantaneous amplitude and frequency of the TEC time series, which exposes the temporal and spatial evolutions of the irregularities from larger structures continuously.