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Geomagnetically induced currents (GICs) in a quasi-meridional power transmission line on the Kola Peninsula are analyzed during the intervals of Pc5/Pi3 (frequency range from 1.5 to 5 mHz) pulsations recorded at the IMAGE magnetometer network. We have analyzed GIC in a transformer at the terminal station Vykhodnoy (68∘ N, 33∘ E) during the entire year of 2015, near the maximum of the 24th Solar cycle. To quantify the efficiency of GIC generation by geomagnetic pulsations, a ratio between power spectral densities of GIC and magnetic field variations is introduced. Upon examination of the geomagnetic pulsation efficiency in GIC generation, the emphasis is given to its dependence on frequency and spatial scale. To estimate pulsation spatial scales in latitudinal and longitudinal directions, the triangle of stations KEV-SOD-KIL has been used. Large-scale pulsations (with a high spectral coherence, low phase difference, and similar amplitudes at latitudinally separated stations) are found to be more effective in GIC generation than small-scale pulsations. The GIC response also depends on the pulsation scale across the electric power line.

Energy circulation in geospace lies at the heart of space weather research. In the inner magnetosphere, the steep plasmapause boundary separates the cold dense plasmasphere, which corotates with the planet, from the hot ring current/plasma sheet outside. Theoretical studies suggested that plasmapause surface waves related to the sharp inhomogeneity exist and act as a source of geomagnetic pulsations, but direct evidence of the waves and their role in magnetospheric dynamics have not yet been detected. Here, we show direct observations of a plasmapause surface wave and its impacts during a geomagnetic storm using multi-satellite and ground-based measurements. The wave oscillates the plasmapause in the afternoon-dusk sector, triggers sawtooth auroral displays, and drives outward-propagating ultra-low frequency waves. We also show that the surface-wave-driven sawtooth auroras occurred in more than 90% of geomagnetic storms during 2014–2018, indicating that they are a systematic and crucial process in driving space energy dissipation. Theoretical studies suggested that plasmapause surface waves related to the sharp inhomogeneity exist and act as a source of geomagnetic pulsations. Here, the authors show direct observations of a plasmapause surface wave and its impacts during a geomagnetic storm using multi-satellite and ground-based observations.

Disturbances in the Interplanetary Magnetic Field (IMF) and solar conditions can affect the geomagnetic field measurements. In the current study, the influence of IMF and solar fluctuations on the nighttime Pc3-5 and Pi2 pulsations at low latitudes is investigated. Geomagnetic data recorded by the Egyptian geomagnetic observatories are used to examine the occurrence of nighttime pulsation events in Egypt. The corresponding daytime data from the Honolulu (HON) INTERMAGNET observatory were used for comparison between nighttime and daytime pulsation activity aiming for a better understanding of their sources. Two pulsation activities occurred on 7 and 27 February 2014 under different IMF and solar conditions were examined. Results of data analysis indicate that geomagnetic field fluctuations (Pc3-5 and Pi2 pulsations) are affected by changes in the IMF and solar conditions. The occurrence of space weather events such as geomagnetic storms and Coronal Mass Ejections (CMEs) can significantly affect the coherence and correlations between the pulsation wave-packets observed at nighttime and daytime suggesting different generation mechanisms for each pulsation event.

Variations in electric and magnetic (EM) fields were examined at two sites: Dhanachuli near the Main Boundary Thrust (MBT) and Patiyasar near the Main Central Thrust (MCT) in Kumaun Himalaya, India. Anomalous EM signatures are defined based on medium-term data recordings. The patterns of anomalous EM signatures are then linked to the occurrence of moderate earthquakes (3.5 ≤ M ≤ 5.0), enhanced along the MCT. The vertical component of the magnetic field is due to microtremors prior to the earthquakes; electric fields also show positive anomalies. Surface waves due to microtemors associated with the earthquakes is reflected in the polarization ratios of geomagnetic data in the Pc4 range (0.01 Hz), a few days prior to each earthquake. In the case of one earthquake, during which suitable data could be retrieved, we observe a frequency change in ULF (Pc1 range) in addition to the enhancement of the Pc4, prior to the event.Plain language summaryThe search for EM precursors of earthquakes continues to be a promising one. In this pursuit, we have chosen a seismologically active region of Kumaun Himalaya and established geo-electromagnetic data acquisition systems. Scanning through about 5 months of data, we were able to detect anomalous variations in data through three independent approaches, which can be reliably ascribed to a seismogenic source. We present here the analysis of the patterns of these anomalous signals vis-à-vis the occurrences of about 15 earthquakes within a 250 km radius of our sites.

Using data from the 2D IMAGE network and magnetic stations located in Russia, Pc5 geomagnetic pulsations with a frequency of ~2.8 mHz, which occurred in the afternoon sector against the background of the magnetic storm of August 27, 2014, preceded by a 5-day period with low magnetic activity, are studied in detail. In two time intervals, at the beginning of the storm and during the period of maximum magnetic activity, instantaneous 2D distributions of Pc5 magnetic field amplitudes on Earth’s surface are plotted. It has been found that the ionospheric sources of Pc5 (vortex Hall currents) have an elliptical shape with a larger axis in the south–north direction. At the beginning of the magnetic storm, a single burst of Pc5 pulsations was detected, the center of the source of which was located at the geomagnetic latitude ~67.5° ( L ~ 6.8 R E ) and moved westward with a velocity of ~0.7 km/s. The estimated size of this ionospheric source is ~150 km in the west–east direction and ~330 km in the south–north direction. During the maximum of the magnetic storm, Pc5 pulsations are produced by two ionospheric sources following each other. These ionospheric sources have a more elongated elliptical shape with axes of ~250 km in the west–east direction and ~670 km in the south–north direction. The centers of these sources were shifted by 4° to a more southern geomagnetic latitude ~63.5° ( L ~ 5 R E ) and moved westward with a velocity of ~1.7 km/s. Estimates of the size of the two-time magnetic field tube in which the resonance MHD waves have been generated and its velocity in the equatorial plane of the magnetosphere are presented.

Several possible lithosphere–atmosphere–ionosphere coupling mechanisms before earthquake occurrence are presented in the literature. They are described by several models with different interaction channels (e.g., electromagnetic, mechanics, chemical, thermal), sometimes in conflict with each other. In this paper, we search for anomalies six months before the Lushan (China) 2013 earthquake in the three geo-layers looking for a possible view of the couplings and testing if one or another is more reliable to describe the observations. The Lushan earthquake occurred in China’s Sichuan province on 20 April 2013, with a magnitude of Mw = 6.7. Despite the moderate magnitude of the event, it caused concern because its source was localized on the southwest side of the same fault that produced the catastrophic Wenchuan event in 2008. This paper applies a geophysical multi-layer approach to search for possible pre-earthquake anomalies in the lithosphere, atmosphere, and ionosphere. In detail, six main increases in the accumulated seismic stress were depicted. Anomalous geomagnetic pulsations were recorded in the Chengdu observatory, sometimes following the increased stress. Atmosphere status and composition were found to be anomalous in several periods before the earthquake, and, spatially, the anomalies seem to appear firstly far from the upcoming earthquakes and later approaching the Longmenshan fault where the Lushan earthquakes nucleated. The Formosat-3 data identified interesting anomalies in the altitude or electron content of the ionospheric F2 peak in correspondence with seismic and atmospheric anomalies 130 days before the earthquake. In addition, the total electron content showed high anomalous values from 12 to 6 days before the earthquake. We compared the anomalies and tried to explain their correspondences in different geo-layers by the lithosphere–atmosphere–ionosphere coupling models. In particular, we identified three possible couplings with different mechanisms: a first, about 130 days before the earthquake, with a fast (order of one day) propagation delay; a second, about 40 days before the earthquake occurrence, with a propagation delay of few days and a third from 2.5 weeks until one week before the event. Such evidence suggests that the geo-layers could interact with different channels (pure electromagnetic or a chain of physical-chemical processes) with specific propagation delays. Such results support the understanding of the preparation for medium and large earthquakes globally, which is necessary (although not sufficient) knowledge in order to mitigate their impact on human life.

This study investigates the occurrence and distribution of geomagnetic pulsations (Pc2–Pc5) over South America during 2014, analyzing their dependence on magnetic latitude, local time, and geomagnetic activity. Geomagnetic field data were obtained from the Embrace magnetometer network, which spans Brazil and Argentina and includes regions influenced by the Equatorial Electrojet (EEJ) and the South Atlantic Magnetic Anomaly (SAMA). Both continuous and discrete wavelet transforms (CWT and DWT) were employed to analyze non-stationary signals and reconstruct pulsation activity during quiet and disturbed geomagnetic periods. The results reveal that Pc5 and Pc3 pulsations exhibit a pronounced diurnal peak around local noon, with significantly stronger and more widespread activity under storm conditions. Spatial analyses highlight localized enhancements near the dip equator during quiet times and broader latitudinal spread during geomagnetic disturbances. These findings underscore the strong modulation of pulsation activity by geomagnetic conditions and offer new insights into wave behavior at low and mid-latitudes. This work contributes to understanding magnetosphere–ionosphere coupling and has implications for space weather prediction and geomagnetically induced current (GIC) risk assessment in the South American sector.

Gujarat region (India) was struck by an earthquake of magnitude 5.3 on June 14, 2020 at 14:43 UTC near Bhachau city in Kachchh district in the state of Gujarat, with a depth of 20 km at the epicentre of 23.38° N, 70.36° E. In order to study the earthquake precursors for this event, data from the Induction Coil Magnetometer (LEMI-30) installed at the Badargadh Multi-Parameter Geophysical Observatory (MPGO) was analyzed for the period from January 1 to June 16, 2020. This station is located ~20 km from the epicentre of this earthquake. We observed that a clear geomagnetic burst was identified in the raw data of the B x and B y components in the LEMI-30 data before this earthquake. Geomagnetic amplitude bursts were identified 6 to 18 days and 2 days before this earthquake with a frequency of 0.01 to 0.02 Hz. Polarization ratio (PR) analysis revealed an anomalous signal on June 11, 2020 with PR values increasing to 1.4. The planetary index (K p ) and disturbance storm time index (D st ) due to the Sun‒Earth interaction are also very low (K p = 0.3 and D st = –6 nT) from June 10 to 16, 2020. In order to understand the dynamics of seismic processes, fractal dimensional analysis is also applied to magnetic data. Fractal dimension values also corroborate with the results of PR analysis, which showed a similar anomaly on June 11, 2020. The ULF geomagnetic data was further analyzed by applying the band-pass filtered data instead of the raw data in the period range from 10 to 45 seconds and derived the Z/X amplitude ratio in the Pc3 band. We found an upward trend and a downward trend from June 10, 2020. Enhanced polarization ratios were detected in the reconstructed components using the EMD technique which are linked to the current earthquake. It has been clearly demonstrated that the EMD method can be used to isolate noise and thus improve the identification of simultaneous short-term geomagnetic variations/anomalies. Therefore, in our study, we have clearly differentiated their origin, whether external (the Sun‒Earth interactions) or internal (local changes in conductivity in the area of the preparation).

—The paper examines the possibility of occurrence of global geomagnetic disturbances during earthquakes, events that have been documented by observations and reported in numerous publications in leading Russian geophysical journals. Validation of the above phenomenon could become a significant discovery in geophysics. Therefore, these results require thorough verification. The comparison of the disturbances presented in the publications with the data from high-latitude magnetometer stations has shown that all the morphological features of the long-period disturbances (with quasi periods of 10–40 min) identify them as characteristic manifestations of the activation of the magnetospheric-ionospheric current system in the auroral latitudes. Thus, the detected disturbances represent a mid-latitude response to electrojet variations in the auroral region and are not related to seismic activity. The short-period disturbances (with a characteristic period less than 1 min) proved to be either a coseismic geomagnetic response to a surface seismic wave or a burst of Pc 3 pulsations of magnetospheric origin, occasionally coinciding with the occurrence of a distant earthquake. This study clearly demonstrates that the identification of anomalous disturbances requires the efforts of both earthquake physics specialists and space weather experts.

A study is performed of geomagnetic pulsations with periods from unity to tens of minutes and associated geomagnetically induced currents. The relationship is considered between the efficiency of current excitation by geomagnetic pulsations and the parameters of the interplanetary magnetic field and solar wind plasma at different delays. Data from measuring the geomagnetic field and geomagnetically induced currents in the Russian North and Finland are used for analysis. It is shown that the efficiency of excitation of geomagnetically induced currents by pulsations is higher if the solar wind speed does not fall notably below 500 km s −1 for several hours.