Global Variations of the Total Electron Content in the Equatorial Ionosphere during the Annular Solar Eclipse of June 21, 2020

Abstract

A solar eclipse (SE) causes recordable disturbances in all subsystems of the Earth–atmosphere–ionosphere–magnetosphere system and in geophysical fields. The response of the system to an SE substantially depends on the eclipse magnitude, the solar cycle phase, the atmospheric and space weather, the season, the time, and the observation coordinates. Manifestations of the response are also influenced by the observation technique. Despite the fact that the effect of a solar eclipse on the ionosphere has been studied for approximately 100 years, a number of unresolved issues remain. The purpose of this study is to describe the results of our analysis of temporal total electron content (TEC) variations caused by the annular solar eclipse on June 21, 2020, in the equatorial ionosphere. The authors analyzed 132 time dependences of the TEC that covered an extensive region with an eclipse. The maximum magnitude (M_max = 0.9940) of the eclipse, which began at 06:39:59 UT, was observed in northern India in Uttarakhand and lasted 38 s. Space weather conditions on June 21, 2020, were favorable for studying the effects associated with the SE. To reveal the response of the ionosphere to the annular SE on June 21, 2020, the GPS signal recordings were processed. Time variations of the TEC in the ionosphere on reference days and on the SE day of June 21, 2020, were analyzed on a global scale. For this purpose, the results of measurements at twelve stations and eleven GPS satellites were used. The dependences of the absolute and relative TEC value decreases caused by the SE on a time of day are studied. The lowest value of the TEC decrease (–2…–3 TECU) was observed in the morning. In the daytime and in the evening hours, it reached –4…–6 TECU. The relative decrease in the TEC barely depended on a time of day and reached –30…–35%. No stable dependence of the TEC decrease on the eclipse magnitude was found. The relative value of the TEC decrease depended on the SE magnitude, i.e., smaller values of the SE magnitude corresponded to smaller values of the relative TEC decrease. The duration of the TEC reduction exceeded the duration of the eclipse by 1.5–2.5 h. The time of reaching the minimum TEC values in the daytime and the evening hours delayed by 10–20 min with respect to the time of reaching the maximum SE magnitude. Wave-like disturbances of the TEC were practically absent. Undisturbed TEC values and the TEC values disturbed by the eclipse substantially depended on the location of stations and the trajectory of satellites, which was associated with the influence of equatorial ionization anomaly. This is the main peculiarity of ionospheric effects of the SE at latitudes 0°–30° N.