Observation of Ionospheric Plasma Motion over Kharkiv During Solar Eclipses on September 1, 2016, and June 10, 2021

The results of observations of the motion of the ionospheric plasma over Ukraine during the partial (up to 37.8% of the Sun's area) solar eclipse on September 1, 2016, which occurred in the magnetically conjugate region for Kharkiv (near the island of Madagascar, 37° 35’ S, 47° 26’ E), and during June 10, 2021 partial (4.4% in area) solar eclipse over Kharkiv (49° 36’ N, 36° 18’ E) are presented. The Kharkiv incoherent scatter radar and digital ionosondes were used for these ionospheric observations. On September 1, 2016, changes were observed in the temporal variations of the vertical component of the ionospheric plasma drift velocity, which probably caused by the solar eclipse in the southern hemisphere and associated with the processes of interaction through the magnetosphere between the ionospheres of the magnetically conjugate regions of the Earth's southern and northern hemispheres. These changes were manifested in a decrease in the absolute value of the velocity of the downward motion of plasma in the ionosphere over Ukraine with an extremum 42 min after the maximum phase of the solar eclipse in the magnetically conjugate region. This effect is opposite to effect that generally caused by the solar eclipse over Kharkiv. The beginning of the velocity deviation coincided in time with the maximum phase of the solar eclipse, and the end was 1 h 16 min after the instant of greatest eclipse. The velocity deviation amplitude increased with altitude and amounted to 5–45 m/s at altitudes of 200–580 km. The velocity deviation was accompanied by a similar deviation in the temporal variation of the critical frequency with a maximum decrease of 0.7 MHz and in the temporal variation of ionospheric F2 peak height with a maximum increase of 30 km. The response of the ionosphere to the partial solar eclipse on June 10, 2021 with a small obscuration of the Sun (0.112 in diameter, 0.044 in area) at the studied altitudes of 180–500 km was very weak or absent at all, in contrast to results of previous observations of solar eclipses over Kharkiv with greater obscuration of the Sun's disk area (0.31 and more).