Geomagnetic Effect of the Solar Eclipse of June 10, 2021

A solar eclipse (SE) pertains to rare high-energy natural phenomena. For instance, a change in the internal (thermal) energy of the air in a layer only 100 m in height attains 10¹⁸ J while the power of the process is on the order of terawatts. The energy of the processes produced by the SE in the upper atmosphere and geospace is significant. For instance, the thermal energy of the ionospheric plasma in a volume of ~10¹⁹ m³ decreases by 10¹¹ J. The magnetic field in a volume of ~10²¹ m³ decreases by 50 nT, and its energy by 10¹⁵ J. SEs are accompanied by disturbances in all subsystems of the Earth–atmosphere–ionosphere–magnetosphere system. Disturbances in the upper atmospheric and ionospheric parameters act to inevitably produce geomagnetic field variations. At present, geophysicists have no consensus on how SE manifests itself in the geomagnetic field. The available data are inconsistent. Most of the researchers believe that the geomagnetic effect of SE exists. In some cases, the temporal variations in the geomagnetic field, as a whole, repeat the changes in the illumination of the Earth’s surface; in other cases, they may be ahead or delayed by ~1 hour in relation to the changes in illumination. Most often, the geomagnetic effect is studied in the region of the total SE where it should be the most pronounced. The further the observatory is located from the umbra, the more difficult it is to relate the magnetic variations to the SE. Finding the response of the geomagnetic field to the SE is a complicated task. A possible response is “masked” by variations of another nature. Moreover, the magnitude and sign of the geomagnetic field disturbance significantly depend on the state of space weather, season, local time, location of the magnetic observatory, and, of course, the magnitude of the eclipse. Therefore, the study of the effect of SEs on the geomagnetic field remains an important task. The purpose of this study is to present the results of analysis of temporal variations in the geomagnetic field observed by the International Real-Time Magnetic Observatory Network (INTERMAGNET) during the SE of June 10, 2021. The main feature of this eclipse was that the SE was annular (maximum magnitude M_max ≈ 0.943). The annular SE occurred on June 10, 2021 with a commencement time 08:12:20 UT over Canada. The Moon’s shadow moved across the Atlantic Ocean, Greenland, the Arctic Ocean, the North Pole, and the northern parts of Europe and Asia. A partial SE occurred in Mongolia and China, and it ceased at 11:33:43 UT. The annularity was observed from 10:33:16 to 10:36:56 UT over Greenland. The analysis of the geomagnetic effect was based on the INTERMAGNET database. The data were processed with 1-min temporal resolution and 0.1-nT level resolution, and temporal variations in the X, Y, and Z components recorded at 15 magnetic observatories were studied. The SE was found to be accompanied by an aperiodic decrease in the X component by 31–36 to 2–3 nT. A decrease in this level attained a maximum value during the maximum magnitude of the annular eclipse, and the magnitude of the effect rapidly decreased with distance southward. For the southernmost observatories, we were not able to determine a decrease in the mean value. Other geomagnetic field components had hardly any change in the course of the SE. The SE was also accompanied by quasi-periodic variations in the level of the X component. The amplitude of these variations decreased from 4 to 1 nT with distance away from the region of the annular eclipse. The period of the quasi-periodic disturbances was observed to be 40 ± 2 min. These disturbances are suggested to be produced by atmospheric gravity waves under the action of the solar eclipse. The relative changes in the atmospheric gravity wave pressure were estimated to be ~1–2%. The estimates of both aperiodic and quasi-periodic effects are in agreement with the observations, which confirms the mechanism for their generation.