Influences of the Earth’s Magnetic Field on the Transient Electromagnetic Process in the Geoelectric Field: an Experimental Study

—A mathematical model of the influence of the Earth’s magnetic field (the Hall effect) on results of the controlled source transient electromagnetic (TEM) method has been elaborated. For identification of this effect, we propose a schematic layout of the experimental grounded system with a pulsed loop source and signals recording by radial receive lines equally spaced relative to the loop. The 2018–2019 special field experiments were conducted in the Tatar region of the West Siberian Lowland with an aim to estimate the Hall effect contributions to the TEM method. To detect the Hall effect, transient electromagnetic responses were measured mainly by four receive lines radiating from a 500×500 m square loop. Analysis of the TEM results processing aimed at improving the signal quality and reducing the interference revealed a great similarity in signals from the radial lines, which is theoretically possible only under the Hall effect. Comparison of the field signals with the theoretical ones enabled estimation of the components caused by the Hall effect, in particular, conductivity at ~0.002 S/m.

Modelling of geomagnetically induced currents in the Czech transmission grid

We investigate the maximum expected magnitudes of the geomagnetically induced currents (GICs) in the Czech transmission power network. We compute a model utilising the Lehtinen–Pirjola method, considering the plane-wave model of the geoelectric field, and using the transmission network parameters kindly provided by the operator. We find that the maximum amplitudes expected in the nodes of the Czech transmission grid during the Halloween storm-like event are about 15 A. For the “extreme-storm” conditions with a 1-V/km geoelectric field, the expected maxima do not exceed 40 A. We speculate that the recently proven statistical correlation between the increased geomagnetic activity and anomaly rate in the power grid may be due to the repeated exposure of the devices to the low-amplitude GICs. Graphical Abstract

Modeling the Effects of the Factors Affecting IGF in Coastal Areas and Variation of IGF in Jiaodong Peninsula of China Based on Finite Element Method

Based on finite element method, we develop a model of the induced geoelectric field (IGF) occurring in land-sea boundary regions during large geomagnetic field disturbances. The model is used first to study the effects of the changes in the lithospheric conductivity, ionospheric current, and ocean depth on the distribution of IGF in a typical land-sea boundary region. The results show that the changes in the lithospheric conductivity and ionospheric current (frequency, magnitude and direction) have major effects and ocean depth has minor effect on IGF in coastal areas. Then by incorporating a realistic 3-D conductivity variation of Jiaodong Peninsula (JDP) in China obtained from measured data, the model is used to simulate the IGF variation in JDP covering its land-sea boundaries for east-west and north-south ionospheric currents. The results show a new aspect that extremely large IGF development on the land side of the coastal bay areas perpendicular to the currnet compared to plane coastal areas. The results can stimulate detailed investigations of IGF (and GIC, geomagnetically induced current) in coastal areas.

Katz Fractal Dimension of Geoelectric Field during Severe Geomagnetic Storms

We are concerned with the time series resulting from the computed local horizontal geoelectric field, obtained with the aid of a 1-D layered Earth model based on local geomagnetic field measurements, for the full solar magnetic cycle of 1996–2019, covering the two consecutive solar activity cycles 23 and 24. To our best knowledge, for the first time, the roughness of severe geomagnetic storms is considered by using a monofractal time series analysis of the Earth electric field. We show that during severe geomagnetic storms the Katz fractal dimension of the geoelectric field grows rapidly.

Geoelectric field response characteristics analysis of floor roadway surrounding rock fracture caused due to coal seam mining

The fracture of rocks surrounding the floor roadway during the mining of the working face of a coal mine is a complicated spatiotemporal process due to the superimposed action of multiple stress fields on the surrounding rock mass. Using the surrounding rock of a floor roadway in the working face of the Huainan Pan’er Mine as the research subject, we conducted real-time monitoring using geoelectric field monitoring technology, and found the spatiotemporal response law of the geoelectric field in the process of regional rupture and damage of engineering rock masses under a complex stress field environment. The results show that (1) the time series response characteristics and spatial distribution of the geoelectric field signal are closely related to the stress distribution and damage evolution of the surrounding rock mass; (2) the rupture and damage degree of the goaf floor significantly increased when the working face was pushed through the monitoring area for 20–40 m. During this process, the excitation current dropped by 4–12 mA, and the self-potential pulse fluctuation amplitude was greater than 400 mV; (3) from the beginning of the monitoring process to the end of the monitoring, the self-potential in the damaged area decreased by 250 mV, and the self-potential in the mudstone layer below the damaged area increased by 140 mV. The electrons released into the environment around the damaged rock mass during the severe impact phase of mining did not flow back to the damaged area, and the positive charge in the damaged rock mass gradually accumulated in the complete rock mass in units of rock strata; (4) when superimposed and supported by anchor rod and cables, the bearing capacity of the shallow bearing circle of the roadway was enhanced, and the excitation current presented a step-like overall increase during mining of the working face with a small drop after every significant increase. This result is of significance in monitoring the evolutionary process of real-time failure of rock masses under complex stress environments using geoelectric field information and in improving the quality of geoelectric field monitoring technology testing applications in the future.

Space weather impact on ground-based technological systems

This review, offered for the first time in the Russian scientific literature, is devoted to various aspects of the problem of the space weather impact on ground-based technological systems. Particular attention is paid to hazards to operation of power transmission lines, railway automation, and pipelines caused by geomagnetically induced currents (GIC) during geomagnetic disturbances. The review provides information on the main characteristics of geomagnetic field variability, on rapid field variations during various space weather mani-festations. The fundamentals of modeling geoelectric field disturbances based on magnetotelluric sounding algorithms are presented. The approaches to the assessment of possible extreme values of GIC are considered. Information about economic effects of space weather and GIC is collected. The current state and prospects of space weather forecasting, risk assessment for technological systems from GIC impact are discussed. While in space geophysics various models for predicting the intensity of magnetic storms and their related geomagnetic disturbances from observations of the interplanetary medium are being actively developed, these models cannot be directly used to predict the intensity and position of GIC since the description of the geomagnetic field variability requires the development of additional models. Revealing the fine structure of fast geomagnetic variations during storms and substorms and their induced GIC bursts appeared to be important not only from a practical point of view, but also for the development of fundamentals of near-Earth space dynamics. Unlike highly specialized papers on geophysical aspects of geomagnetic variations and engineering aspects of the GIC impact on operation of industrial transformers, the review is designed for a wider scientific and technical audience without sacrificing the scientific level of presentation. In other words, the geophysical part of the review is written for engineers, and the engineering part is written for geophysicists. Despite the evident applied orientation of the studies under consideration, they are not limited to purely engineering application of space geophysics results to the calculation of possible risks for technological systems, but also pose a number of fundamental scientific problems