Ionospheric Processes during the Partial Solar Eclipse above Kharkiv on June 10, 2021

A solar eclipse (SE) provides a researcher with a rare opportunity to follow the dynamics of the Earth’s system (its shells)—the atmosphere, the ionosphere, and the magnetosphere—and variations in the geophysical fields over an interval of a few hours. Different solar eclipses induce significantly different disturbances in this system. The parameters of these disturbances depend on the onset time of a solar eclipse, the state of space weather, the season, the solar cycle phase, the geographic coordinates, and the degree of the solar disk occultation during a solar eclipse. It should be kept in mind that each of the SEs exhibits its own individual characteristics. The purpose of this paper is to analyze the results of ionosonde observations of the ionospheric disturbances accompanying the SE above the city of Kharkiv on June 10, 2021. At the city of Kharkiv, the maximal observed magnitude of the SE was М_max ≈ 0.11 (more precisely, 0.112) and the relative area of the solar disk occultation was А_max ≈ 4.4%. The eclipse started at 10:42 UT (13:42 LT) and ended at 12:12 UT (15:12 LT). The maximal magnitude was observed at 11:28 UT (14:28 LT). To study the features of variations in the virtual heights and the frequencies, we used a digital ionosonde located at the Radio Physical Observatory of the V. N. Karazin Kharkiv National University. The analysis of the space weather showed that, during the SE, as well as at the reference time intervals on June 6 and 9, 2021, the space weather conditions were favorable for observing wave disturbances, which is evidenced by the index value K_p ≈ 0.3. The frequency and altitude characteristics of the ionosphere obtained by vertical sounding were analyzed, and the features of the ionospheric processes, which accompanied the partial SE but were absent on the reference day, were determined. During the SE, wave activity in the ionosphere became stronger. The wave trains, which were observed at an altitude of the F₂ layer maximum, had periods of 5 and 14 min, while the relative amplitudes of oscillations in the electron density were 0.6 and 1.25%, respectively. At an altitude of 240 km, the relative amplitude of waves with a period of ~14 min increased by 3%. The 14-min period pertains to the atmospheric gravitaty waves, while the 5-min period pertains to the waves of electromagnetic nature. A sharp and considerable increase (from 380 to 560 km) in the virtual height of the radio wave reflection from the F₂ region was observed close to the moment of the greatest SE magnitude. A weak decrease (by less than 3.3%) in the electron density, which lagged behind the maximal eclipse magnitude by 12.5 min, was detected. The rates of the electron loss (1.33 × 10^–3 s^–1) and the ion production (3 × 10⁸ m^–3s^–1) were estimated.