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At the altitude of low-Earth-orbiting satellites, most details of lithospheric magnetic anomalies observed near surface are attenuated, and only slowly decaying long-wavelength magnetic anomalies can be detected. Long-wavelength magnetic anomalies are generated by large-scale magnetized rocks in the Earth's crust and uppermost mantle at depths shallower than the Curie depth. Interpretation of such lithospheric magnetic anomalies has been used in geological mapping, crustal composition and structure studies, plate tectonic reconstruction, and geodynamics. To introduce the origin of long-wavelength magnetic anomalies at a global scale, we first reviewed satellite magnetic anomaly maps in early periods and calculated anomaly maps using four main lithospheric magnetic field models, including the CHAOS-7, CM6, MF7, and CSES models. Then, based on the result of the CHAOS-7 model at 500 km altitude, 29 long-wavelength magnetic anomalies with amplitudes greater than 4 nT were identified and their geological origins were reviewed. Among these, there were twenty magnetic anomalies over continents and nine over the ocean. The long-wavelength magnetic anomalies over continental areas were mostly located in Precambrian basements related to the Archean nuclei, Proterozoic terrane, and iron-rich formations, with a few located in the orogenic background. The long-wavelength magnetic anomalies in the ocean region were all located in oceanic plateau, generally related to the breakup of Gondwana during the Cretaceous Period, and have the characteristics of thickened crust. Hence, the long-wavelength magnetic anomalies reveal a significant magnetization difference in the deep crust during crustal growth, a key issue that requires further study. Compared to satellite magnetic surveys in some other nations, detecting lithospheric magnetic anomalies by satellite started relatively late in China. The China Seismo-Electromagnetic Satellite (CSES) was launched in February 2018. It was China's first satellite designed to monitor earthquakes with multiple geophysical payloads, including magnetometers capable of measuring weak signals from the lithosphere. The Macau Science Satellite-1 (MSS-1) was launched in 2023 and is specially used for monitoring the geomagnetic field in low latitudes. Furthermore, a subsequent CSES-02 satellite is planned to be launched in 2024. With the vigorous development of satellite magnetic surveys in China, it is expected that progressively more Chinese researchers will pay attention to long-wavelength magnetic anomalies and promote the study of their origin.

Low Earth orbit (LEO) satellites have emerged as a primary tool for global geomagnetic field detection and model refinement, owing to their wide coverage, high resolution, and absence of geographical limitations. This paper provides a comprehensive review of the history, key characteristics, measurement accuracy, and future trends in LEO satellite magnetic field measurements. The first part of the paper outlines the evolution of LEO satellites, highlighting their unique advantages. The focus then shifts to the calibration methodology for in-orbit LEO satellite magnetic measurements, with a specific emphasis on vector magnetic field intrinsic calibration and alignment algorithms. Calibration results are presented to demonstrate the effectiveness of these methodologies. In the third section, the paper introduces the theory behind global geomagnetic field modeling. An overview of current global geomagnetic field models is provided, encompassing their sources, spatial resolutions, and other relevant attributes. The paper concludes by presenting the global morphology and features of the main field, lithospheric field, magnetospheric, and ionospheric field. Despite the significant progress enabled by LEO satellite technology, global geomagnetic field modeling faces challenges such as limited spatio-temporal resolution. To address this, incorporating near-surface observation data and continuously optimizing modeling technology are deemed essential solutions.

Long-wavelength (>500 km) magnetic anomalies originating in the lithosphere were first found in satellite magnetic surveys. Compared to the striking magnetic anomalies around the world, the long-wavelength magnetic anomalies in China and surrounding regions are relatively weak. Specialized research on each of these anomalies has been quite inadequate; their geological origins remain unclear, in particular their connection to tectonic activity in the Chinese and surrounding regions. We focus on six magnetic high anomalies over the (1) Tarim Basin, (2) Sichuan Basin (3) Great Xing’an Range, (4) Barmer Basin, (5) Central Myanmar Basin, and (6) Sunda and Banda Arcs, and a striking magnetic low anomaly along the southern part of the Himalayan-Tibetan Plateau. We have analyzed their geological origins by reviewing related research and by detailed comparison with geological results. The tectonic backgrounds for these anomalies belong to two cases: either ancient basin basement, or subduction-collision zone. However, the geological origins of large-scale regional magnetic anomalies are always subject to dispute, mainly because of limited surface exposure of sources, later tectonic destruction, and superposition of multi-phase events.

Abstract Earth’s atmosphere, whose ionization stability plays a fundamental role for the evolution and endurance of life, is exposed to the effect of cosmic explosions producing high energy Gamma-ray-bursts. Being able to abruptly increase the atmospheric ionization, they might deplete stratospheric ozone on a global scale. During the last decades, an average of more than one Gamma-ray-burst per day were recorded. Nevertheless, measurable effects on the ionosphere were rarely observed, in any case on its bottom-side (from about 60 km up to about 350 km of altitude). Here, we report evidence of an intense top-side (about 500 km) ionospheric perturbation induced by significant sudden ionospheric disturbance, and a large variation of the ionospheric electric field at 500 km, which are both correlated with the October 9, 2022 Gamma-ray-burst (GRB221009A).

The Zhangheng-1 electromagnetic satellite is the space-based observation platform of China's stereoscopic earthquake observation system. Its scientific objective is to obtain the global geomagnetic field, electromagnetic field (waves), ionospheric plasma parameters, and high-energy particles for monitoring the dynamic variation of the ionosphere and the seismo-ionospheric disturbances over China and its surrounding areas to compensate for the deficiency of the ground-based observation system. The project explores new ways of earthquake monitoring and prediction by using space science. The first test probe of the Zhangheng-1 electromagnetic satellite series was successfully launched in February 2018, and has been stably operating in orbit for more than four years. The second is an operational probe that will be launched in early 2023. The in-flight commissioning test and cross-calibration work show that the Zhangheng-1 electromagnetic satellite can provide good data quality to support geophysics and space physics studies, and has obtained valuable scientific results in recent years. The global geomagnetic reference model built by Zhenghang-1 data is the first global geomagnetic field model built using only Chinese satellite data, allowing Chinese scientists to take an important role in the computation of the global geomagnetic reference model (IGRF) for the first time in over a century. The ionospheric electron density 3D model based on Zhangheng-1 satellite data can present the ionospheric structure characteristics. In natural hazards monitoring, Zhangheng-1 has shown good response ability to disturbances related to earthquakes, volcano eruptions, and geomagnetic storms. In terms of the lithosphere-atmosphere-ionosphere coupling mechanism study, the full-wave calculation method can provide the electromagnetic field changes between the lithosphere-ionosphere waveguide and the ionospheric wave propagation feature. The results from the full-wave model prove the capability of the Zhangheng-1 satellite's electromagnetic payloads to detect low-frequency electromagnetic emissions induced from the earthquake epicenter. The simulation and observation studies suggest that the Zhangheng-1 satellite can reflect seismic activities, very low frequency (VLF) transmitter, magnetic anomalies in the lithosphere, and lightning activities in the atmosphere. These recent scientific results show that the Zhangheng-1 electromagnetic satellite is consistent with other similar types of electromagnetic satellites worldwide, indicating its great potential in scientific application.

On May 21, a Ms6.4 earthquake occurred in Yangbi, Yunnan Province. Less than 5 ​h later, on May 21, follows a Ms7.4 earthquake in Madoi, Qinghai Province. In this study, multiple parameters are studied from CSES-01 satellite and GNSS. The parameters include the electron density from LAP, energetic particle flux from HEPP, electric field spectrum from EFD, induced magnetic field spectrum from SCM, and global TEC from ground-based GNSS receivers. In the time scale, all parameters changed on May 15, 17 and 18. The relative amplitude of Ne is more than 200%. In space scale, the clear enhancement focus on the southeast of the epicenter of Madoi, Qinghai, and the shape of the focus region is like a clockwise-30°-rotated rectangle, which is about 45° in length and 20° in width. Moreover, there appeared enhancement in the conjugated region. According to the day-to-day analysis of the low-frequency (75–90 Hz) spectrum of EFD and SCM payloads, the relationship of the increment on May 18 could be confirmed with the successive two earthquakes. The energetic particle fluxes enhanced on May 20. All those changes are located in the east of the following epicenter and appeared just several days before, which could be well explained by the Lithosphere-Atmosphere-Ionosphere theory.

Abstract With the accumulation of data, it is possible to study the long-term variation of Fluxgate Magnetometers (FGM) of High Precision Magnetometer (HPM) onboard the China Seismo-Electromagnetic Satellite (CSES). The calibration method of HPM depends on an assumption that the linear parameters of FGM, including the gain factors, the offsets, and non-orthogonal angles are stable. However, HPM exhibits some unexpected trends in the scalar residuals when processed according to the assumption. Study on the residual finds out that under changing space thermal conditions, the non-orthogonal angles of FGM change periodically, suggesting that the data calibration method we used before should be modified. A multi-dimensional polynomial model is established for defining the change of non-orthogonal angles of FGM as a function of the sun incidence angles, geographic latitude and sensor temperature. Apply the polynomial model to data from August 2018 to May 2021, the standard deviation of the scalar residuals is reduced to around 0.5 nT and tends to be more random and in line with the normal distribution. Meanwhile, the variation trend in gain factors and offset factors are eliminated. Results show that the model can correctly reflect the period variation of the non-orthogonal angles of FGM with the space thermal conditions. Graphical Abstract

From August to October 2018, a series of strong earthquake (EQ) events occurred in southeast Asia and northern Oceania (22°S to 0°N, 115°E to 170°E) within 50 days. In this paper, we analyze the features of ionospheric plasma perturbations, recorded by the Plasma Analyzer Package (PAP) and Langmuir probe (LAP) onboard the China Seismo-Electromagnetic Satellite (CSES-01), before four EQs with magnitudes of Ms 6.9 to Ms 7.4. The ion parameters such as the oxygen ion density (No+), the ion drift velocity in the vertical direction (Vz) under the conditions of geomagnetic storms, and strong EQs are compared. The results show that within 1 to 15 days before the strong EQs, the No+ and the electron density (Ne) increased while the electron temperature (Te) decreased synchronously. Meanwhile, the Vz significantly increased along the ground-to-space direction. The relative variation of No+ and Vz before the strong EQs is more prominent, and the Vz is not easily influenced by the geomagnetic storm but is susceptible to the seismic activities. Our results suggest that the anomaly of ionospheric plasma perturbations occurring in this area is possibly related to the pre-EQ signatures.

This study presents signatures of seismo-ionospheric perturbations possibly related to the 14 July 2019 \begin{document}$ {M}_{w} $\end{document}7.2 Laiwui earthquake, detected by a cross-validation analysis of total electron content (TEC) data of the global ionospheric map (GIM) from GPS and plasma parameter data recorded by the China Seismo-Electromagnetic Satellite (CSES). After separating pre-seismic ionospheric phenomena from the ionospheric disturbances due to the magnetospheric and solar activities, we have identified three positive temporal anomalies, around the epicenter, at 1 day, 3 days and 8 days before the earthquake (14 July 2019), along with a negative anomaly 6 days after the earthquake. These results agree well with the TEC spatial variations in latitude–longitude–time (LLT) maps. To confirm these anomalies further, we employed the moving mean method (MMM) to analyze ionospheric plasma parameters (electron, \begin{document}$ {\mathrm{O}}^{+} $\end{document}and \begin{document}$ {\mathrm{H}\mathrm{e}}^{+} $\end{document}densities) recorded by the Langmuir probe (LAP) and Plasma Analyzer Package (PAP) onboard the CSES. The analysis detected on, on Day Two, Day Four, and Day Seven before the earthquake, remarkable enhancements along the orbits around when in proximity to the epicenter. To make the investigations still more convincing, we compared the orbits on which anomalous readings were recorded to their corresponding four nearest revisiting orbits; the comparison did indeed indicate the existence of plasma parameter anomalies that appear to be associated with the Laiwui earthquake. All these results illustrate that the unusual ionospheric perturbations detected through GPS and CSES data are possibly associated with the \begin{document}$ {M}_{w}7.2 $\end{document} Laiwui earthquake, which suggests that at least some earthquakes may be predicted by alertness to pre-seismic ionospheric anomalies over regions known to be at seismic risk. This case study also contributes additional information of value to our understanding of lithosphere–atmosphere–ionosphere coupling.

This work analyzed the Ms 7.1 earthquake occurred at 01:47 UT on September 8th, 2021, in Acapulco City, Guerrero, Mexico (17.12° N, 99.6° W, N and W represent north and west, respectively) with a 30 ​km focal depth by using multiple parameters recorded by China Seismo-Electromagnetic Satellite-1 (CSES-1). In this work, we studied the electron density (Ne) recorded by langmuir probe and O+ from plasma analyzer package at a height of 507 ​km 15 days before the earthquake. After excluding the plasma density variations caused by the geomagnetic storms on August 28th and September 7th, the results revealed that the nighttime Ne, and O+ increased on September 2nd (6 days before the earthquake) simultaneously within ±10° in latitude and ±10° in longitude around the epicenter. In addition, the enhancement was also found in electron density profile (EDP) between 200 ​km and 300 ​km derived from GNSS radio occultation data. Not only the different particle species (Ne and O+) at 507 ​km, but also electron density at 507 ​km and EDP in lower ionosphere shown anomalies 6 days before the earthquake. Basing on the results, we suggest that the enhancements of Ne, O+, and EDP on September 2nd are possible related to the Mexico Ms 7.1 earthquake on September 8th.

To explore the correlation between earthquakes and the pre-earthquake ionospheric shallow frequency (ELF) electric field perturbations phenomenon, the paper investigated the pre-earthquake ionospheric perturbations phenomenon, and then the Spatio-temporal evolution characteristics of the electromagnetic field before and after the global Ms ≥6.0 strong earthquakes from 2019 to 2021 were statistically analyzed. In this paper, the power spectrum data of the ELF (19.5–250 Hz) band of ionospheric electric field observed by the China Seismo-Electromagnetic Satellite (CSES) electric field detector are preclinically processed by the C-value method. A stable background field observation model was constructed using the data from 75 to 45 days before the earthquake observed by the CSES in the range of 15° above the epicenter. Then, the amplitude of the spatial electric field disturbance over the epicenter relative to the background field is extracted. Finally, the superposition analysis method statistically analyzes the spatial and temporal evolution of the spatial electric field before and after the earthquake with different characteristics. The statistical results show that the anomalies first appear in the fourth period (15–19 days before the earthquake) and the third period (10–14 days before the earthquake) and then reach the most vital and most evident during the pro-earthquake period (4 days before the earthquake and the day of the earthquake); In terms of the intensity of the anomalies caused, the magnitude seven earthquakes are stronger than the magnitude 6.0–7.0 earthquakes, and marine earthquakes are stronger than land earthquakes; in terms of the ease of observing the anomalies, the magnitude 7.0 and above are more accessible to observe than the magnitude 6.0–7.0 earthquakes, and marine earthquakes are more accessible to observe than land earthquakes.

To explore the correlation between earthquakes and spatial ultra-low frequency electric field disturbances and to study the phenomenon of seismic ionospheric disturbances, this study uses 3 years of electric field ULF band data from 2019 to 2021 observed by the electric field detector carried by the CSES to identify anomalous disturbances using the anomaly automatic detection algorithm based on empirical mode decomposition for the 2,329 seismic events of magnitude not less than 5.0 and the electric field ULF disturbances in this period are analyzed by Superposed Epoch Analysis, and the statistical results are compared and analyzed in depth by earthquake location and different magnitudes in terms of both spatial and temporal scales and spatial distribution. The results show that: 1) There is a correlation between earthquakes of magnitude not less than 5.0 and ultra-low frequency disturbances in the electric field. The abnormal disturbance mainly occurred 11 days before the earthquake, 2 days before the earthquake to the day of the earthquake, and the location of the earthquake is within 200 km from the epicenter. 2) Sea earthquakes can observe more pre-seismic anomalous electromagnetic disturbances than land earthquakes. 3) In terms of earthquake magnitude, the larger the magnitude, the earlier the pre-earthquake anomalous disturbances appear and the wider the range of anomalies. This study provides an effective way to explain seismic ionospheric phenomena, and also provides a reference for the application of electromagnetic monitoring satellites in earthquake prediction and early warning as well as disaster prevention and mitigation.

The theoretical development of Schumann Resonances has spanned more than a century as a form of global natural electromagnetic resonances. In recent years, with the development of electromagnetic detection technology and the improvement in digital processing capabilities, the connection between Schumann Resonances and natural phenomena, such as lightning, earthquakes, and Earth’s climate, has been experimentally and theoretically demonstrated. This article is a review of the relevant literature on Schumann Resonance observation experiments, theoretical research over the years, and a prospect based on space-based observations. We start with the theoretical background and the main content on Schumann Resonances. Then, observations and the identification of Schumann Resonance signals based on ground and satellite data are introduced. The research and related applications of Schumann Resonances signals are summarized in terms of lightning, earthquakes, and atmosphere. Finally, the paper presents a brief study of Schumann Resonances based on the China Seismo-Electromagnetic Satellite (CSES) and preliminary ideas about how to improve the identification and application of space-based Schumann Resonances signals.

Abstracts: In this study, we present the variations of electron density (Ne) and electron temperature (Te) in the nighttime ionosphere above the areas of seismic activities by the statistical method. The Ne and Te were observed by the CSES over ~2.5 years from May 2018 to December 2020. In the statistical analysis, the Ne and Te closed to the epicenters both in space and time are compared with their background values. The data associated with aftershocks, at high latitudes, and during high magnetic activity periods are carefully checked and finally removed from the statistics, to avoid spurious effects and the high variability of the ionosphere on the statistics. The results show that: (1) During nighttime, anomalous ionospheric perturbations related to earthquakes with magnitudes larger than 5 are in evidence; (2) According to the histogram distributions of Ne and Te perturbations, the positive variations of Ne and the negative variations of Te are related to seismic activities; (3)The significant variations of positive Ne and negative Te related to earthquakes mainly occurred ~1–7 days and ~13–15 days before the earthquakes respectively, and within 200 ​km from the epicenters.

A retrospective analysis of complex geophysical data around the time of the two most powerful earthquakes that occurred in Alaska and had magnitudes M = 8.2 (29 July 2021) and M = 9.2 (28 March 1964), respectively, is carried out. The aim of the research is to assess the maximum possible magnitude of the electric field of a seismogenic nature that penetrated the ionosphere/plasmasphere, which could cause the ionospheric effects observed experimentally. Theoretical calculations have shown that under the geophysical conditions that existed before these earthquakes (favorable for the penetration of the seismogenic field into the ionosphere), the maximum value of a quasi-static electric seismogenic field in the ionosphere, perpendicular to geomagnetic field lines (tens of hours/units of days before the earthquake) for earthquakes with magnitudes M = 8–9 could reach 1–2 mV/m. Such values are sufficient for the formation of a plasmaspheric ULF-ELF-VLF-duct, which is formed in the vicinity of the geomagnetic field-line passing through the epicenter of the earthquake under the influence of a seismogenic electric field that penetrated into the ionosphere/plasmasphere. This leads to an anomalous amplification of the captured ULF-ELF-VLF waves, ULF (DC-16 Hz), ELF (6 Hz–2.2 kHz), VLF (1.8–20 kHz), not only above the epicenter of the future earthquake, but also at the point magnetically conjugated with the epicenter of the earthquake, testifying to the formation of such a duct, stretched along the geomagnetic field from one hemisphere to another, and formed on closed L-shells shortly before the earthquake. This result is confirmed by the measurements of the mission of the CSES satellite (China-Seismo-Electromagnetic Satellite) for the 29 July 2021 earthquake with magnitude M = 8.2.

As a parameter that quantitatively measures the shielding effect of the Earth’s magnetic field on energetic particles, the geomagnetic cutoff rigidities will change significantly with the long-term change of geomagnetic field. In this article, by using the numerical simulation method, combined with the variation trend of the Earth’s main field International Geomagnetic Reference Field (IGRF) model and the energetic particles’ windows (EPWs), the variation characteristics of the cutoff rigidities of geomagnetic energetic particles in the vertical direction from 1965 to 2025 were studied. The study found that there is a close relationship between the cutoff latitude corresponding to the cutoff rigidities and the background magnetic field intensity, but they are not in a simple linear relationship. The changes of the cutoff rigidities and geomagnetic field in the northern and southern hemispheres are asymmetric. The weakening of the geomagnetic field will push the cutoff latitudes toward the near equatorial region in the southern hemisphere, but for northern hemisphere the phenomenon is not always credible. In the northern hemisphere, the areas of EPWs will decrease at a relative rate of 0.03%/yr, but in the southern hemisphere, it will increase at a rate of about 0.05%/yr to 0.12%/yr. The long-term trajectory of the positions of the EPWs’ central points do not correspond to geomagnetic poles, nor the magnetic dip poles, relatively speaking, its position is closer to the geomagnetic poles. The study can be used for a long-term forecasting of cutoff rigidities caused by background geomagnetic field variations.

Abstract The Sichuan Basin magnetic anomaly is the most striking regional aeromagnetic anomaly in South China. It is characterized by a continuous large-scale linear magnetic anomaly and contains long-wavelength constituents which could still be detected on satellites. However, Sichuan Basin is covered by 4 to 10 km thick non-magnetic sedimentary layers from Neoproterozoic to Cenozoic, which conceals the magnetic sources in the Precambrian basement and makes it difficult to explore the geological origin of the Sichuan Basin magnetic anomaly. In this study, we applied 3D inversion to the magnetic data, and then compared our inverted susceptibility model with geological maps. We found that the spatial distribution of the Sichuan Basin magnetic anomaly controls the range of the rigid basement beneath Sichuan Basin and it is surrounded by the widespread Neoproterozoic magmatic complexes. Based on our analysis, we proposed that the geological origin of the Sichuan Basin magnetic anomaly might be related to the craton-scale Neoproterozoic magmatic event, which has played an important role in the stabilization of the basement and the evolution of the deep crust in Sichuan Basin.

Since the CSES (China Seismo-Electromagnetic Satellite) has been in orbit, it has detected a large number of constant-frequency electromagnetic disturbances (CFEDs), which are horizontal lines on the spectrum. In this paper, we present an algorithm for automatic recognition of CFEDs based on computer vision technology. The relevant results are of great significance for analysis of perturbation events and mining of the transformation laws of global space events. First, a grayscale spectrogram is obtained; then, a horizontal convolution kernel is used to enhance the horizontal edge features of the grayscale graph, and finally, black-and-white binarization is performed to complete data preprocessing. The preprocessed data are then fed into an unsupervised cluster model for training and recognition to realize automatic recognition of CFEDs. Experimental results show that the CFED recognition algorithm proposed in this paper is effective, with a recognition accuracy of more than 98%.

The recognition algorithm of the lightning whistler wave, based on intelligent speech, is the key technology to break the bottleneck of massive data and study the temporal and spatial variation rules of the lightning whistler wave. However, its recognition effect depends on the hyperparameters determined by manual experiments repeatedly, which takes a great deal of time and cannot guarantee the best recognition effect of the model. Therefore, we proposed the lightning whistler wave recognition algorithm based on grey wolf optimization (GWO). In this paper, the GWO algorithm is used to automatically find the best value of hyperparameters of Long Short-Term Memory (LSTM) in their limited searching space. Here we consider the number of hidden units (hu) and learning rate (lr) as the hyperparameters to be optimized, and the spatial coordinate (hu, lr) as the grey wolf position. By the end of the GWO process, we obtain the position of the wolf king α with the optimal hu and lr searched by the GWO algorithm. Then we use the optimal hu and lr to configure LSTM and perform supervised learning on the train set to obtain the final lightning whistler wave speech recognition model. Through experimental verification, the recognition model based on the GWO not only overcomes the uncertainty of the traditional model relying on manual finetuning of parameters and realizes the mechanism of automatic search and acquisition of hyperparameters, but also its recognition effect improves by about 2% in accuracy, F1score, and other metrics compared with the model trained by manually setting hyperparameters.

Nowadays, the possibility that medium-large earthquakes could produce some electromagnetic ionospheric disturbances during their preparatory phase is controversial in the scientific community. Some previous works using satellite data from DEMETER, Swarm and, recently, CSES provided several pieces of evidence supporting the existence of such precursory phenomena in terms of single case studies and statical analyses. In this work, we applied a Worldwide Statistical Correlation approach to M5.5+ shallow earthquakes using the first 8 years of Swarm (i.e., from November 2013 to November 2021) magnetic field and electron density signals in order to improve the significance of previous statistical studies and provide some new results on how earthquake features could influence ionospheric electromagnetic disturbances. We implemented new methodologies based on the hypothesis that the anticipation time of anomalies of larger earthquakes is usually longer than that of anomalies of smaller magnitude. We also considered the signal’s frequency to introduce a new identification criterion for the anomalies. We find that taking into account the frequency can improve the statistical significance (up to 25% for magnetic data and up to 100% for electron density). Furthermore, we noted that the frequency of the Swarm magnetic field signal of possible precursor anomalies seems to slightly increase as the earthquake is approaching. Finally, we checked a possible relationship between the frequency of the detected anomalies and earthquake features. The earthquake focal mechanism seems to have a low or null influence on the frequency of the detected anomalies, while the epicenter location appears to play an important role. In fact, land earthquakes are more likely to be preceded by slower (lower frequency) magnetic field signals, whereas sea seismic events show a higher probability of being preceded by faster (higher frequency) magnetic field signals.

This work is an attempt to critically analyze the correlation between great deep-focus undersea earthquake and possible ionospheric anomalies. The significant TEC (total electron content) temporal and spatial anomalies were detected over the epicenter of 2007 Mw7.5 Jakarta–Java earthquake, and they coincide well with the striking plasma anomalies in the ionosphere in situ observed by the LEO (low Earth orbit) satellite. The localization and synchronization of the disturbances during the earthquake suggest that these ionospheric anomalies are highly related to this large undersea earthquake. In order to identify this correlation, we made efforts to distinguish seismo-associated signals from large electromagnetic noise due to solar and geomagnetic activities, natural non-seismic sources and known artificial signals. Nevertheless, the difficulties of this work should be recognized and approached with caution. This special (deep-focus and undersea) case study here provides us with valuable information on the study of lithosphere–atmosphere–ionosphere (LAI) coupling process and reminds us that deep-focus undersea seismic events need to be treated more carefully and discreetly in the future.

Abstract Based on data from the Van Allen Probes and ZH‐1 satellites, relativistic electron enhancements in extremely low L‐shell regions (reaching L∼3) were observed during August 2018 major geomagnetic storm (minimum Dst≈−190 nT). Contrary to what occurs in the outer belt, such an intense and deep electron penetration event is rare and more interesting. Strong whistler‐mode (chorus and hiss) waves, with amplitudes 81–126 pT, were also observed in the extremely low L‐shell simultaneously (reaching L∼2.5) where the plasmapause was suppressed. The bounce‐averaged diffusion coefficient calculations support that the chorus waves can play a significantly important role in diffusing and accelerating the 1–3 MeV electrons even in such low L‐shells during storms. This is the first time that the electron acceleration induced by chorus waves in the extremely low L‐shell region is reported. This new finding will help to deeply understand the electron acceleration process in radiation belt physics.

Previous studies have reported that, before or after occurrences of strong earthquakes, some low earth orbit satellites recorded ionospheric disturbances, including electromagnetic emissions and plasma fluctuations over the epicenter region or its conjugate point. Theoretically speaking, due to some electromagnetic coupling effect, electromagnetic emissions from the earthquake preparation zone could propagate from the lithosphere to the atmosphere, and could reach the ionosphere, even up to the inner magnetosphere. This paper introduces the electric field detector (EFD) onboard the ZhangHeng-1 satellite (ZH-1). The EFD is designed to measure electric field fluctuations within the broad frequency range of DC to 3.5 MHz, divided into 4 channels: ULF (DC–16 Hz), ELF (6 Hz–2.2 kHz), VLF (1.8 kHz–20 kHz) and HF (18 kHz–3.5 MHz). The sampling rates of the channels are 125 Hz, 5 kHz, 50 kHz and 10 MHz, respectively. The EFD includes 4 spherical probes mounted on a over 4.5 m boom and an electronic box inside the satellite module. The resolution of the EFD is 1 μV·m-1·Hz-1/2 at frequencies from DC to 16 Hz, and the sensitivity is 0.1 μV·m-1·Hz-1/2 at frequencies from 6 Hz to 2.2 kHz, 0.05 μV·m-1·Hz-1/2 in the band 1.8 kHz to 20 kHz, and 0.1μV·m-1·Hz-1/2 from 20 kHz to 3.5 MHz. The dynamic range from DC to 20 kHz is over 120 dB, and over 96 dB from 20 kHz to 3.5 MHz. The EFD has two observation modes: survey mode and burst mode. The survey mode concentrates primarily on electric field power density values; the burst mode provides high sampling rate waveform data. The detailed configuration of the EFD onboard the ZH-1 is also introduced in this paper. During the six months’ orbit test phase, the EFD recorded a number of natural electromagnetic emissions. Preliminary analysis of these data suggests that the EFD performs well onboard the ZH-1 and is meeting the requirements of the scientific objectives of ZH-1.

The aim of this work is to validate the China Seismo-Electromagnetic Satellite 01 (CSES-01) Electric Field Detector (EFD) measurements through the analysis of the instrument response to various inputs: (a) geomagnetic field variations, (b) plasma density depletions, and (c) electromagnetic signals from natural and artificial sources such as Schumann resonance and VLF (Very Low Frequency) antennas. The knowledge of the geomagnetic induced electric field vs×B (where vs is the satellite speed and B and the local magnetic field), and the plasma variations effect, described by the Orbit Motion Limited (OML) theory, are key parameters to determine the expected theoretical values of the EFD sensors potentials data. Based on the CSES on-board measurements of plasma parameters and geomagnetic field, a direct quantitative validation is presented. In addition, the electromagnetic signals detection capability is checked but only qualitatively confirmed, since the ionospheric complexity does not allow an accurate theoretical computation of waves modulation. The quantitative comparison highlights the very good agreement between observed and theoretical potentials values during average condition. Conversely, in case of strong electric fields, the OML theory shows partial inability in reproducing the actual space plasma conditions resulting in a reduced theoretical values reliability. Finally, both natural and artificial electromagnetic signals are satisfactorily identified showing a reliable sensitivity in different frequency bands.

This paper investigates the impact characteristics of the 4 November 2021 magnetic storm across different frequency bands based on the electric field data (EFD) from the China Seismo-Electromagnetic Satellite (CSES), categorized into four frequency bands: ULF (Ultra-Low-Frequency, DC to 16 Hz), ELF (Extremely Low-Frequency, 6 Hz to 2.2 kHz), VLF (Very Low-Frequency, 1.8 to 20 kHz), and HF (High-Frequency, 18 kHz to 3.5 MHz). The study reveals that in the ULF band, magnetic storm-induced electric field disturbances are primarily in the range of 0 to 5 Hz, with a significant disturbance frequency at 3.9 ± 1.0 Hz. Magnetic storms also enhance Schumann waves in the ULF band, with 8 Hz Schumann waves dominating in the southern hemisphere and 13 Hz Schumann waves dominating in the northern hemisphere. In the ELF band, the more pronounced anomalies occur at 300 Hz–900 Hz and above 1.8 kHz, with the 300 Hz–900 Hz band anomalies around 780 Hz being the most significant. In the VLF band, the electric field anomalies are mainly concentrated in the 3–15 kHz range. The ELF and VLF bands exhibit lower absolute and relative disturbance increments compared to the ULF band, with the relative perturbation growth rate in the ULF band being approximately 10% higher than in the ELF and VLF bands. Magnetic storm-induced electric field disturbances predominantly occur in the ULF, ELF, and VLF bands, with the most significant disturbances in the ULF band. The electric field perturbations in these three frequency bands exhibit hemispheric asymmetry, with strong perturbations in the northern hemisphere occurring earlier than in the southern hemisphere, corresponding to different Dst minima. No electric field disturbances were observed in the HF band (above 18 kHz). The conclusions of this paper are highly significant for future anti-jamming designs in spacecraft and communication equipment, as well as for the further study of magnetic storms. [ABSTRACT FROM AUTHOR]

The occurrence of space weather events, notably geomagnetic storms driven by various solar wind structures, can significantly alter Earth's electromagnetic environment. In this study, we examined the interplanetary origins and statistical distribution of 384 geomagnetic storms ( D s t m i n   ≤ −50 nT) that occurred from September 1996 to December 2023. We statistically analyzed the correlations between storm intensity and solar wind parameters (SWPs) across different subsets. The results indicate that (1) the solar activity level, indicated by the sunspot number (SSN), and the number of geomagnetic storms during the first four years of the 25th solar cycle were intermediate, compared to the first four years of the 23rd and 24th solar cycles. Specifically, ICME-related structures caused 80% of the strong storms ( D s t m i n   ≤ −100 nT) and 34% of the moderate storms (−100 nT < D s t m i n   ≤ −50 nT) from 2020 to 2023. (2) The storm intensity correlated with the peak and/or time-integral values of the southward interplanetary magnetic field (IMF B s ), the dawn–dusk electric field ( E y ), the Akasofu's function (ε), and dynamic pressure ( P s w ) to varying extents. Strong storms exhibited higher correlation levels than moderate ones and ICME-related storms showed larger correlation levels compared to those driven by other sources. (3) Compared with the storms from 1996-09 to 2000-08, the storms that occurred from 2020 to 2023 had lower correlations with the peak values of the IMF B s and E y but higher correlations with the peak value of ε and the time-integral values of the IMF B s , E y , P s w , and ε. (4) Among the 174 events that featured continuous southward IMF during the storm's main phase, the duration of southward IMF during about 66.7% of moderate storms and 51.5% of strong storms were less than 13 h. Continuous southward IMF resulted in more direct and efficient energy coupling, enhancing the correlation between the peak values of SWPs and storm intensity but weakening the relationships with the time-integral values of SWPs. Notably, when the southward IMF persisted for a longer duration (e.g., ∆t > 13 h), the continuous energy input further enhanced correlations with both peak and integral values of SWPs, leading to stronger overall correlations with storm intensity. This analysis sheds light on the intricate relationships between geomagnetic storms and their solar wind drivers, emphasizing the significant influence of ICME-related structures and the duration of southward IMF on storm intensity. [ABSTRACT FROM AUTHOR]

Identifying seismic CH4 anomalies via remote sensing has been verified as a legitimate method. However, there are still some problems, such as unknown reliability due to the complex characteristics of seismic anomalies. In this study, a multi-dimensional and multi-scale methane seismic anomaly extraction process for remote sensing was constructed with the Robust Satellite Technique (RST) based on the Atmospheric Infrared Sounder (AIRS) CH4 data and then applied to the 2023 Türkiye–Syria earthquake. This study obtained the two-dimensional temporal–spatial distribution of methane anomalies and temporal variation in the anomaly index. Based on this, the three-dimensional profile structure of the 8-day methane anomaly was extracted to determine the reliability of the anomaly. Finally, based on the daily methane anomaly, combined with atmospheric circulation and backward trajectory analysis as auxiliary tools, the influence of air mass migration was excluded to enhance the accuracy of CH4 anomaly determination. The results show that the three-dimensional anomalous structure is consistent with the geological characteristics of tectonic activities, and it appears as a "pyramid" or "inverted pyramid" type in a three-dimensional space. The anomalies caused by air mass migration can be eliminated by combining them with synoptic-scale circulation motion. The time series calculated at the epicenter or a certain point in a region may not accurately reflect the influence of regional or specific tectonic activity in the atmosphere. Thus, the optimal determination of the range and magnitude of atmospheric anomalies caused by tectonic activities is a difficult task for future research. [ABSTRACT FROM AUTHOR]

Driven by the scientific objective of geophysical field detection and natural hazard monitoring from space, China launched an electromagnetic satellite, which is known as the China Seismo-Electromagnetic Satellite (CSES-01), on 2 February 2018, into a circular sun-synchronous orbit with an altitude of about 507 km in the ionosphere. The CSES-01 has been in orbit for over 6 years, successfully exceeding its designed 5-year lifespan, and will continually operate as long as possible. A second identical successor (CSES-02) will be launched in December 2024 in the same orbit space. The ionosphere is a highly dynamic and complicated system, and it is necessary to comprehensively understand the electromagnetic environment and the physical effects caused by various disturbance sources. The motivation of this report is to introduce the typical electromagnetic waves, mainly in the ELF/VLF band (i.e., ~100 Hz to 25 kHz), recorded by the CSES-01 in order to call the international community for deep research on EM wave activities and geophysical sphere coupling mechanisms. The wave spectral properties and the wave propagation parameters of those typical EM wave activities in the upper ionosphere are demonstrated in this study based on wave vector analysis using the singular value decomposition (SVD) method. The analysis shows that those typical and common natural EM waves in the upper ionosphere mainly include the ionospheric hiss and proton whistlers in the ELF band (below 1 kHz), the quasiperiodic (QP) emissions, magnetospheric line radiations (MLR), the falling-tone lightning whistlers, and V-shaped streaks in the ELF/VLF band (below 20 kHz). The typical artificial EM waves in the ELF/VLF band, such as power line harmonic radiation (PLHR) and radio waves in the VLF band, are also well recorded in the ionosphere. [ABSTRACT FROM AUTHOR]

The ionospheric quasi-periodic wave is a type of typical and common electromagnetic wave phenomenon occurring in extremely low-frequency (ELF) and very low-frequency ranges (VLF). These emissions propagate in a distinct whistler-wave mode, with varying periodic modulations of the wave intensity over time scales from several seconds to a few minutes. We developed an automatic detection model for the QP waves in the ELF band recorded by the China Seismo-Electromagnetic Satellite. Based on the 827 QP wave events, which were collected through visual screening from the electromagnetic field observations, an automatic detection model based on the Transformer architecture was built. This model, comprising 34.27 million parameters, was trained and evaluated. It achieved mean average precision of 92.3% on the validation dataset, operating at a frame rate of 39.3 frames per second. Notably, after incorporating the proton cyclotron frequency constraint, the model displayed promising performance. Its lightweight design facilitates easy deployment on satellite equipment, significantly enhancing the feasibility of on-board detection. [ABSTRACT FROM AUTHOR]

In this study, we focus on the interactions and interrelated effects among the transient luminous events (TLEs) recorded at the Luoding ground station (22.76° N, 111.57° E), the lightning activities observed by the World Wide Lightning Location Network, and the ionospheric electric field deduced from the China Seismo-Electromagnetic Satellite (CSES). The results show that on 25 September 2021, the signal-to-noise ratio of the Schumann resonance at the first mode of 6.5 Hz and the second mode of 13 Hz dropped below 2.5 during the TLEs. A significant enhancement in the energy in extremely low frequencies (ELFs) occurred, and the power spectral density increased substantially. Distinct lightning whistler waves were found in the very low frequency (VLF) band, further indicating that the energy could possibly have been excited by the lightning. Our results suggest that the observations of the electric field from the satellite could possibly be utilised to monitor the lower-atmospheric lightning and its impact on the space environment. [ABSTRACT FROM AUTHOR]

Relevant studies have shown that methane gas has a close relationship with seismic activity. The concentration of methane released within a tectonic zone can reflect the intensity status of tectonic activities, which is important for seismic monitoring. In this study, the January 2020 Xinjiang Jiashi earthquake was taken as the research object, and the mature Robust Satellite Technique (RST) algorithm was used to characterize the L3-level methane product data from the hyperspectral sensor, Atmospheric Infrared Sounder (AIRS), installed on the Earth Observing System (EOS) AQUA satellite at the monthly scale, 8-day scale and daily scale. An analysis of the spatial and temporal distribution of methane was carried out for before and after the earthquake based on the 3D structural condition of the gas, and the 3D structural conditions of the 8-day scale were introduced. An 8-day scale 3D structural condition was introduced and migration validation was performed, and the results showed that (1) the seismic methane anomaly-extraction process proposed in this study is feasible; (2) the 3D contour features indicated that the methane anomalies that occurred before the Jiashi earthquake were caused by geogenic emissions; (3) the anomaly-extraction algorithm from this study did not extract the corresponding anomalies in the non-seismic year, which indicated that the anomaly-extraction algorithm of this study has some degree of feasibility; and (4) the migrated validation of the Wenchuan earthquake of May 2008 further suggested that methane anomalies at the time of the Wenchuan earthquake were caused by the earthquake. [ABSTRACT FROM AUTHOR]

In this study, we focus on the effect among the Transient Luminous Events (TLEs) at Luoding (22.76° N, 111.57° E), the lightnings by the World Wide Lightning Location Network, and the ionospheric electric field from the China Seismo-Electromagnetic Satellite. The results show that on September 25, 2021, the signal-to-noise ratio of the Schumann Resonance at the first mode of 6.5 Hz and the second mode of 13 Hz dropped below 2.5 during the TLEs. A significant enhancement of the energy in ULF occurred, and the power spectral density increased substantially. Distinct lightning whistler waves were found in VLF band, further indicating the energy could possibly be excited by the lightnings. Our results indicate that the observations of electric field from the satellite could possibly be utilized to monitor the lower atmospheric lightnings and their impact on the space environment. [ABSTRACT FROM AUTHOR]