Variations in the geomagnetic field that accompanied the 10 June 2021 solar eclipse
Authors: Chernogor L. F. , Golub M. Yu. , Luo Y. , Tsymbal A. M. , Shevelev M. B. 
Published: October 2022

Urgency. At present, the existence of the geomagnetic effect of solar eclipses (SEs) is in question. The data presented in the literature are contradictory. Some researchers assert that the amplitude of the north-south component of the main geomagnetic field increases, while others that it decreases. The third group of researchers notes that this amplitude does not change at all, but instead the amplitude of the west-east component shows variations. In some cases, observations confirm the mechanism for the geomagnetic effect caused by disturbances in the Sq current system, while in other cases observations contradict with the mechanism. The difficulties that are encountered in observing the SE geomagnetic effect are caused by the fact that the magnetic field is subjected to the influence of many energy sources. The magnitude of the geomagnetic effect depends not only on the magnitude (phase) of the solar eclipse but also on the state of space weather, geographic coordinates of data acquisition, local time, season, etc. Therefore, the study of the geomagnetic effect from each new solar eclipse remains an urgent problem. The main feature of the 10 June 2021 Solar eclipse is its annularity. The maximum magnitude did not exceed 0.943, and the eclipse obscuration 89%.

The aim of this work is to present the results of analysis of variations in the geomagnetic field that were recorded by the INTERMAGNET during the 10 June 2021 SE.

Methods and Methodology. To analyze the effects in the main Earth’s magnetic field, the INTERMAGNET data have been utilized. The data have been analyzed from 15 magnetic observatories located between 77.47°-N and 48.17°-N latitude where the maximum phase varied from 0.943 to 0.124. The analysis was performed with 1-min temporal resolution providing a 0.1-nT resolution. To determine spectral content of the quasi-periodic variations, the systems spectral analysis has been used, which combines mutually complementary the short-time Fourier transform, the wavelet transform employing the Morlet wavelet as a basis function, and the Fourier transform in a sliding window with a width adjusted to be equal to a fixed number of harmonic periods.

Results. An aperiodic geomagnetic effect of a solar eclipse has been detected and explained; it consists in a decrease by not greater than 30 nT in the level of the north-south component. The effect is explained by a variation in the ionospheric current density in the west-east direction as a result of a decrease in the electron density during the eclipse. A quasi-periodic geomagnetic effect of a solar eclipse has been revealed; it is explained by the generation of atmospheric gravity waves. The wave acts to modulate the ionospheric electric current, as well as to drag the electrons inducing additional quasi-periodic ionospheric current with a period equal to the wave period. The amplitude of the quasi-periodic variations was observed to be a few nanoteslas. The systems spectral analysis provided more precise values of periods of quasi-periodic variations in the geomagnetic field accompanying the solar eclipse, approximately 20 min and 35 min.

Conclusions. The aperiodic and quasi-periodic geomagnetic effects are caused by the disturbance (generation) of the ionospheric current.