Holub M. Yu. Temporal Variations in the Level of Geomagnetic Field Fluctuations. – Qualifying scientific paper: a manuscript.
Thesis for a Philosophy Doctor Degree in Physics and Mathematics: Speciality 105
Applied Physics and Nanomaterials. – V. N. Karazin Kharkiv National University,
Ministry of Education and Science of Ukraine, Kharkiv, 2026.
The dissertation is devoted to solving an important problem of applied physics, namely the experimental investigation of temporal variations in the level of geomagnetic field fluctuations caused by natural processes in the Sun–magnetosphere–ionosphere–atmosphere–Earth system. Regularities in the variation of geomagnetic field fluctuations under the influence of solar eclipses, solar flares, geomagnetic storms, earthquakes, and major volcanic eruptions have been established.
The purpose of the dissertation is the experimental investigation of temporal variations in the fluctuation level of the geomagnetic field components, determination of their temporal and spectral characteristics, and identification of the physical mechanisms responsible for their formation.
The first chapter reviews current concepts of the geomagnetic field structure, the mechanisms of its formation, and the main natural and anthropogenic sources of disturbances. Previous studies on the geomagnetic effects of solar eclipses, solar flares, geomagnetic storms, earthquakes, and volcanic activity are analyzed, providing the basis for the objectives of the dissertation.
The second chapter investigates the geomagnetic effects of the solar eclipses of 10 June 2021, 25 October 2022, 14 October 2023, and 8 April 2024. For the 10 June 2021 eclipse, an aperiodic decrease in the X-component of up to 30 nT and quasiperiodic variations with periods of about 20 and 35 min were detected. Analysis of the 25 October 2022 eclipse using data from 15 INTERMAGNET stations revealed a decrease in the X-component by 1–6 nT, an effect lasting 90–180 min, and its dependence on the maximum eclipse obscuration. Data from 10 INTERMAGNET stations for the 14 October 2023 eclipse showed a decrease in the X-component of up to 4–5 nT and enhanced fluctuations with periods of 5–120 min. During the 8 April 2024 eclipse, decreases in the X-, Y-, and Z-components and oscillations with a period of about 60 min and amplitudes of 0.2–4 nT were observed. The geomagnetic effect was found to depend on the eclipse phase, local time, ionospheric current parameters, and the geometry of the Moon's shadow.
The third chapter examines the geomagnetic effects of solar flares and geospace storms. During the X-class solar flares of 6–10 September 2017, the fluctuation level of the H and D components increased by a factor of 3–10, with the largest variations observed in the ranges of 10–100 s and 10–15 min. A statistical database of 153 geomagnetic storms of Solar Cycle 24 (Kp ≥ 5) was compiled. Statistical characteristics of the solar wind, interplanetary magnetic field, and geomagnetic activity indices were determined, showing that Solar Cycle 24 was less active than Solar Cycle 23. Detailed analyses of the storms of 28 April–2 May and 4–7 November 2023 demonstrated that the latter consisted of five successive G1–G3 storms, during which the range of geomagnetic field variations increased by a factor of 20–28 compared with quiet conditions.
The fourth chapter investigates the geomagnetic effects of earthquakes and the Hunga Tonga volcanic eruption. Quasiperiodic geomagnetic variations with delays of about 6 min and 97–106 min were associated with magnetohydrodynamic and atmospheric gravity waves, respectively. The relative electron concentration disturbance reached about 5.3%. Analysis of the eruption revealed the global character of the geomagnetic effect. Six groups of geomagnetic disturbances were identified with propagation velocities of about 4 and 1.5 km/s (MHD waves), about 1 km/s (blast wave), about 500 m/s (atmospheric gravity waves), and about 315 and 200 m/s, most likely associated with Lamb and tsunami waves.
The dissertation establishes the regularities of temporal variations in geomagnetic field fluctuations under the influence of solar eclipses, solar flares, geomagnetic storms, earthquakes, and volcanic eruptions. Characteristic temporal scales, amplitudes, and spectral properties of the fluctuations were determined, together with their relationships to processes in the Sun–magnetosphere–ionosphere–atmosphere–Earth system. The results can be used to improve models of geomagnetic disturbances, enhance space weather monitoring, and assess the impact of geospace processes on natural and technological systems.
