Spatio-temporal disturbances of the Earth’s magnetic field along the Struve Geodetic Arc

Abstract

In 1816-1855, astronomer Friedrich Georg Wilhelm von Struve made the first topographic measurements along a 2822 km long segment of the meridian stretching from northern Norway (70°40′N) to southern Odesa Region (45°19′N) to determine the exact size and shape of the planet. This segment of the meridian is a good testing ground for studying the geomagnetic aspect of solar-terrestrial interactions, as both the main magnetic field of the Earth and the anomalous magnetic field at surface and ionospheric heights change significantly within its boundaries. The article presents the results of a study of the nature of the magnetic storm on May 10-13, 2024, depending on the module and anomalies of the geomagnetic field induction module along the Struve Geodesic Arc. To characterize the Earth's internal magnetic field, digital maps of the induction module and anomalies at heights of 5 and 100 km were developed, and to characterize the magnetic storm, the results of observations of variations in the northern, eastern, and vertical components of the geomagnetic field induction module in 7 magnetic observatories were used. For each observatory, we calculated the induction modulus of the internal magnetic field B_i, the modulus of the main magnetic field (core field) B_IGRF, the amplitude and mean value of the geomagnetic field variation, as well as the variation of the parameter ΔD, which reflects the ratio of the anomaly of the geomagnetic field induction modulus to the B_IGRF field. According to the results of statistical analysis, the dependence of the amplitude of the external geomagnetic field variations and their average values on the modulus of the main magnetic field of the Earth B_IGRF was revealed (R²_AõB/BIGPH = 0.96 and R²_{õB_average/BIGPH} = 0.7, respectively). A slightly lower correlation dependence was observed for the Bx component of the geomagnetic field and B_IGRF (R²_Bx/BIGRF=0.89). The amplitude of variation of the spatio-temporal perturbation of the geomagnetic field δ(ΔD) is also characterized by a high correlation dependence on the B_IGRF module (R²_{Aδ(ΔD)/BIGPH}= 0.96) and naturally increases depending on the latitude of the observatory, from 273 nT at the SUA observatory to 2240 nT at the SOD observatory. The revealed regularity is confirmed by a stronger manifestation of the magnetic storm on May 10-13, 2024 and a shift of its maximum disturbances by 4 degrees to the south compared to the magnetic storm of November 29-31, 2003, during which the B_IGRF field induction module for the northern part of the STRUVE GEODETIC ARC increased by 830÷930 nT. The connection between the maximum manifestation of the geomagnetic storm and regional magnetic anomalies on the Earth's surface and their superposition at an altitude of 100 km was revealed. The connection between the maximum manifestation of the geomagnetic storm and regional magnetic anomalies on the Earth's surface and their superposition at an altitude of 100 km is revealed. The maximum magnitude of the magnetic disturbance is recorded at the Pello station, which is located in the region of the maximum anomalous magnetic field (more than 90 nT at an altitude of 100 km), in contrast to the Mikkelvik station ‒ in the zone of the minimum geomagnetic field, which is partially confirmed by the variation of ΔB anomalies due to the magnetization of their sources by the variation of the external field. The most probable reason for the connection between the amplitude of external field variations and the modulus of the main magnetic field of the B_IGRF and the anomalous magnetic field ΔB is their effect on the formation of ionospheric currents.