Geomagnetic Field Research Articles

Low Geomagnetic Field Intensity in Southern China 6,000 Years Ago

AbstractThe West Pacific Anomaly (WPA), a low geomagnetic field anomaly observed in the 16th to 18th centuries, represents a recently recognized and complex feature of Earth's magnetic field. However, the history of the WPA is still uncertain due to a scarcity of paleointensity data in Southeast Asia. Here, we conducted archeointensity analyses on pottery shards from the Xiajiaoshan site in southern China, dated to 4107 ± 123 BCE. Using Thellier–Coe and Repeated Thellier‐Series Experiment methods, we obtained high‐fidelity paleointensities ranging from 14.1 to 26.4 μT (20.7 ± 4.4 μT). These values are significantly lower than surrounding archeointensity data. We incorporated this new data into ArchKalmag14k paleomagnetic field model, which shows the presence of a geomagnetic field low‐intensity anomaly in Southeast Asia around 6,000 years ago. Our study provides the first absolute paleointensity data for low‐latitude East Asia at that time, suggesting that the WPA may have recurred approximately 6,000 years ago.

Dynamic Parameterization and Optimized Flight Paths for Enhanced Aeromagnetic Compensation in Large Unmanned Aerial Vehicles

Aeromagnetic detection is a geophysical exploration technology that utilizes aircraft-mounted magnetometers to map variations in the Earth’s magnetic field. As a critical methodology for subsurface investigations, it has been extensively applied in geological mapping, mineral resource prospecting, hydrocarbon exploration, and engineering geological assessments. However, the metallic composition of aircraft platforms inherently generates magnetic interference, which significantly distorts the measurements acquired by onboard magnetometers. Aeromagnetic compensation aims to mitigate these platform-induced magnetic disturbances, thereby enhancing the accuracy of magnetic anomaly detection. Building upon the conventional Tolles-Lawson (T-L) model, this study introduces an enhanced compensation framework that addresses two key limitations: (1) minor deformations that occur due to the non-rigidity of the aircraft fuselage, resulting in additional interfering magnetic fields, and (2) coupled interference between geomagnetic field variations and aircraft maneuvers. The proposed model expands the original 18 compensation coefficients to 57 through dynamic parameterization, achieving a 22.41% improvement in compensation efficacy compared with the traditional T-L model. Furthermore, recognizing the operational challenges of large unmanned aerial vehicles (UAVs) in conventional calibration flights, this work redesigns the flight protocol by eliminating high-risk yaw maneuvers and optimizing the flight path geometry. Experimental validations conducted in the South China Sea demonstrate exceptional performance, with the interference magnetic field reduced to 0.0385 nT (standard deviation) during level flight, achieving an improvement ratio (IR) of 4.1688. The refined methodology not only enhances compensation precision but also substantially improves operational safety for large UAVs, offering a robust solution for modern aeromagnetic surveys.

A missing palaeomagnetic signal in Middle Devonian pillow lavas

Summary The configuration of the Earth's magnetic field during the Middle Devonian (394.3–378.9 Ma) is poorly understood. The magnetic signals in Middle Devonian rocks are often overprinted during the Kiaman reverse superchron, obscuring their primary remanence. In other cases, available palaeomagnetic data are ambiguous, conflicting with tectonic reconstructions or dipolar geomagnetic field behaviour. Here, we study the palaeomagnetic signal of Middle Devonian pillow basalts from the Rhenish Massif in Germany. Our rock-magnetic experiments show that the pillow basalts can store and retain magnetisations over time. However, the pillow basalts have a somewhat low initial natural remanent magnetisation (NRM), which is not expected based on their magnetite content. The palaeomagnetic directions determined from alternating field demagnetisation, thermal demagnetisation, and a combination of both, fail to cluster around a common mean. Great circle analyses of these palaeomagnetic directions reveal traces of both Kiaman and present-day field overprints. Our palaeointensity measurements have a very low success rate of < 2 per cent, with only one sample yielding a result of 5.9 µT. This low intensity might explain the low initial NRM of the samples and the lack of interpretable directional data in this study. However, given the very low success rate, this result does not convincingly represent the palaeointensity of the Middle Devonian field. All together, the lack of signal in our Middle Devonian pillow lavas could be a sign of an (ultra-)low, or non-dipolar, or possibly even absent geomagnetic field during the time of formation.

Shared periodicities between the length of day and the geomagnetic field at millennial timescales

Shared periodicities between the length of day and the geomagnetic field at millennial timescales

Physiological magnetic field strengths help magnetotactic bacteria navigate in simulated sediments

Bacterial motility is typically studied in bulk solution, while their natural habitats often are complex environments. Here, we produced microfluidic channels that contained sediment-mimicking obstacles to study swimming of magnetotactic bacteria in a near-realistic environment. Magnetotactic bacteria are microorganisms that form chains of nanomagnets and that orient in Earth’s magnetic field. The obstacles were produced based on micro-computer tomography reconstructions of bacteria-rich sediment samples. We characterized the swimming of the cells through these channels and found that swimming throughput was highest for physiological magnetic fields. This observation was confirmed by extensive computer simulations using an active Brownian particle model. The simulations indicate that swimming at strong fields is impeded by the trapping of bacteria in ‘corners’ that require transient swimming against the magnetic field for escape. At weak fields, the direction of swimming is almost random, making the process inefficient as well. We confirmed the trapping effect in our experiments and showed that lowering the field strength allows the bacteria to escape. We hypothesize that over the course of evolution, magnetotactic bacteria have thus evolved to produce magnetic properties that are adapted to the geomagnetic field in order to balance movement and orientation in such crowded environments.

Physiological magnetic field strengths help magnetotactic bacteria navigate in simulated sediments.

Bacterial motility is typically studied in bulk solution, while their natural habitats often are complex environments. Here, we produced microfluidic channels that contained sediment-mimicking obstacles to study swimming of magnetotactic bacteria in a near-realistic environment. Magnetotactic bacteria are microorganisms that form chains of nanomagnets and that orient in Earth's magnetic field. The obstacles were produced based on micro-computer tomography reconstructions of bacteria-rich sediment samples. We characterized the swimming of the cells through these channels and found that swimming throughput was highest for physiological magnetic fields. This observation was confirmed by extensive computer simulations using an active Brownian particle model. The simulations indicate that swimming at strong fields is impeded by the trapping of bacteria in 'corners' that require transient swimming against the magnetic field for escape. At weak fields, the direction of swimming is almost random, making the process inefficient as well. We confirmed the trapping effect in our experiments and showed that lowering the field strength allows the bacteria to escape. We hypothesize that over the course of evolution, magnetotactic bacteria have thus evolved to produce magnetic properties that are adapted to the geomagnetic field in order to balance movement and orientation in such crowded environments.

Archaeointensity study of pottery from the Maya settlements of La Blanca and Chilonché (Petén, Guatemala): New data to constrain the geomagnetic field evolution in Central America

Archaeointensity study of pottery from the Maya settlements of La Blanca and Chilonché (Petén, Guatemala): New data to constrain the geomagnetic field evolution in Central America

Magnetic Torquers Actuated Satellite Attitude Control Using Linear Parameter Varying Techniques

Abstract In this paper, an H∞ gain scheduling algorithm is proposed to solve a nadir-pointing problem of a small satellite using magnetic torquer actuators only. The time-varying nature of the Earth's geomagnetic field is leveraged, and its measurements can be used to define the scheduling parameters for the synthesis of a linear parameter varying gain scheduling (LPVGS) controller and the design of linear parameter varying (LPV) attitude model of the satellite driven with magnetic torquers. The developed algorithm performs well under the time changing magnetic field and allows the stabilization of the closed-loop satellite system in the presence of external disturbances. Since the stability for the H∞ LPV model is ensured by design, all the simulations presented in this paper are performed using the nonlinear equations of the satellite.

Wandering of the auroral oval 41,000 years ago.

In the recent geological past, Earth's magnetic field reduced to ~10% of the modern values and the magnetic poles shifted away from the geographic poles, causing the Laschamps geomagnetic excursion, about 41 millennia ago. The excursion lasted ~2000 years, with dipole strength reduction and tilting spanning 300 years. During this period, the geomagnetic field's multipolarity resembled outer planets, causing rapid magnetospheric changes. To our knowledge, this study presents the first space plasma analysis of the excursion, linking the geomagnetic field, magnetospheric system, and upper atmosphere in sequence using feedback channels for distinct temporal epochs. A three-dimensional reconstruction of Earth's geospace system shows that these shifts affected auroral regions and open magnetic field lines, causing them to expand and wander toward lower latitudes. These changes likely altered the upper atmosphere's composition and influenced anthropological progress during that era. Looking through a modern lens, such an event would disrupt contemporary technology, including communications and satellite infrastructure.

Engineering Magnetotactic Bacteria as Medical Microrobots.

Nature's ability to create complex and functionalized organisms has long inspired engineers and scientists to develop increasingly advanced machines. Magnetotactic bacteria (MTB), a group of Gram-negative prokaryotes that biomineralize iron and thrive in aquatic environments, have garnered significant attention from the bioengineering community. These bacteria possess chains of magnetic nanocrystals known as magnetosomes, which allow them to align with Earth's geomagnetic field and navigate through aquatic environments via magnetotaxis, enabling localization to areas rich in nutrients and optimal oxygen concentration. Their built-in magnetic components, along with their intrinsic and/or modified biological functions, make them one of the most promising platforms for future medical microrobots. Leveraging an externally applied magnetic field, the motion of MTBs can be precisely controlled, rendering them suitable for use as a new type of biohybrid microrobotics with great promise in medicine for bioimaging, drug delivery, cancer therapy, antimicrobial treatment, and detoxification. This mini-review provides an up-to-date overview of recent advancements in MTB microrobots, delineates the interaction between MTB microrobots and magnetic fields, elucidates propulsion mechanisms and motion control, and reports state-of-the-art strategies for modifying and functionalizing MTB for medical applications.

Drone-Enabled 3D Magnetometric Resistivity Imaging for Geological Hazard Detection: A Feasibility Study of Mapping Fracture Zones

This study proposes a novel drone-based semi-airborne total-field magnetometric resistivity (SA-TFMMR) system for high-resolution detection of conductive fracture zones in geologically hazardous terrains. The system integrates a high-power, low-frequency grounded-wire transmitter with a drone-mounted total-field magnetometer, achieving high survey efficiency and extensive data coverage in mountainous areas. We develop a 3D inversion framework incorporating terrain-adaptive depth weighting, which successfully images a dipping water-saturated fracture zone model beneath a reservoir overburden at a tunnel water gushing accident site. Sensitivity analyses of SA-TFMMR reveal that the effectiveness of detection is controlled by the source-target coupling and the orientation of the target body with respect to the geomagnetic field. Optimal current injection along target strike directions amplifies magnetic anomalies, and orthogonal multi-source configurations can enhance imaging resolution. This UAV-geophysical integration provides a paradigm for pre-disaster monitoring of water-related geohazards.

Regional Seismicity of the Northeastern Tibetan Plateau Revealed by Crustal Magnetic Anomalies

The northeastern Tibetan Plateau (NETP) is located at the front of the northeastward expansion of the Tibetan Plateau and is a tectonically active region with complex faults and intense seismicity. In this study, based on the high-order geomagnetic field model EMM2017, the crustal magnetic anomalies and Curie point depths (CPDs) in the NETP and adjacent areas were investigated. The relationship between the magnetic anomalies, CPDs, and seismic activity was assessed. The results show that strong earthquakes occur mainly in areas where the magnetic anomalies are negative or have a strong-to-weak transition. The CPD is located at 18–42 km. In the NETP, a shallow CPD corresponds to high heat flow. In contrast, in surrounding areas, a deep CPD corresponds to low heat flow. The northeast area from Bayan Har to the Qilian orogenic belt, and the region with a deep CPD in the Qaidam Basin, record the northeastward flow of the Tibetan Plateau. High-magnitude earthquakes are associated with depth changes in the CPD and areas with a shallow CPD. The frequent seismic activity in the NETP can be attributed to the northeastward flow of the Tibetan Plateau caused by a deep heat flux. The results can be used as a reference for the prediction of strong regional earthquakes.

Removal of Outliers in Geomagnetic Field Time Series Using the Hampel Filter

The paper presents a methodology for removing outliers in geomagnetic field time series using the Hampel filter. Quality metrics for binary data classification based on the confusion matrix demonstrated the effectiveness of the method and are comparable to those for similar algorithms used for outlier removal in 1-second magnetograms of the international INTERMAGNET network. Outliers identified using the developed methodology for the period 2019-2022 at the Ak-Suu base station exhibit a seasonal distribution pattern that correlates well with thunderstorm activity. The method enhances the quality of preliminary data processing for the geomagnetic monitoring network of the Research Station of the Russian Academy of Sciences, specifically by automating the procedure of magnetograms outliers filtering.

The Cross‐Over From Viscous to Inertial Lengthscales in Rapidly‐Rotating Convection

AbstractConvection is the main heat transport mechanism in the Earth's liquid core and is thought to power the dynamo that generates the geomagnetic field. Core convection is strongly constrained by rotation while being turbulent. Given the difficulty in modeling these conditions, some key properties of core convection are still debated, including the dominant energy‐carrying lengthscale. Different regimes of rapidly rotating, unmagnetized, turbulent convection exist depending on the importance of viscous and inertial forces in the dynamics, and hence different theoretical predictions for the dominant flow lengthscale have been proposed. Here we study the transition from viscously dominated to inertia‐dominated regimes using numerical simulations in spherical and planar geometries. We find that the cross‐over occurs when the inertial lengthscale approximately equals the viscous lengthscale. This suggests that core convection in the absence of magnetic fields is dominated by the inertial scale, which is hundred times larger than the viscous scale.

Analysis of the seasonal and solar effect on the vertical magnetic transfer function at Eskdalemuir Observatory, Scotland

SUMMARY Geomagnetic observations at Eskdalemuir observatory in Southern Scotland reveal reduced amplitudes in the vertical component variations compared with the horizontal components for periods of less than an hour. A subsurface high conductivity feature has previously been suggested to account for this anomaly. However, past studies have overlooked the effect of seasonal source changes and impact of solar activity on external geomagnetic field variations. The vertical magnetic transfer function — referred to as the tipper — relates temporal variations in the vertical magnetic field to those in the horizontal magnetic field and is sensitive to lateral electrical conductivity contrasts in the subsurface. Quantifying the seasonal variations in the tipper helps to identify times when external field variations minimally bias tipper estimates, thereby providing a more accurate representation of subsurface conductivity. Ionospheric current systems, particularly during geomagnetic storms, may violate the plane wave assumption underlying tipper estimation at mid-latitudes. This may allude to a more complex source geometry responsible for magnetic field variations. Our study quantifies and proposes a correction for space weather-driven external field contributions to observations for periods shorter than 1 hr. Using high-quality digital magnetic field data with a 1-min sampling rate from 2001 to 2019, we estimate the tipper at Eskdalemuir, revealing seasonal differences that increase with periods between 1000 s and 10 000 s. After finding that tipper estimates during the 2016 time-series are least affected by seasonal effects, we used 1-s time-series and a simple empirical model to quantify the daily variability of the tipper. The model consists of annual and semi-annual terms plus a term proportional to either the $F10.7$ cm solar flux or geomagnetic $A_p$ index. Neither model fits the data to within the expected error, but the model that uses $A_p$ has better fit. Tipper estimates from temporary site deployments are affected by these seasonal external variations, and we correct those obtained at sites near Eskdalemuir during a recent field experiment using this model.

A study of O/X wave data assimilation and inversion for ionospheric vertical electron density profiles

Vertical sounding of the ionosphere yields ionograms that reflects the relationship between virtual height and frequency, and electron density profiles can be obtained by inversion of the ionogram. The existing vertical sounding ionogram inversion is mainly based on the model method, but this method has poor stability. Influenced by the geomagnetic field, the electric wave splits into O-wave and X-wave when it propagates in the ionosphere, and this study considers introducing X-wave into the ionogram inversion, and adopts the data assimilation method to improve the stability of the inversion by adding more physical sounding information. Specifically, we take the X-wave trace of the ionogram as the observation value, and the electron density profile obtained from the inversion of the O-wave trace of the ionogram as the background value. Then, the kalman filtering method is used to continuously fuse the observation information into the background information, and correct the background electron density profile. Finally, we select some typical ionograms to verify and analyze the assimilation algorithm, and compared the results with the inversion results of Reinisch algorithm. The results show that the calculated virtual heights of the profiles obtained by the joint inversion of the O-wave and X- wave coincide better with the measured virtual heights, and the fitting error between the synthetic traces of the inverted profiles and the measured traces can be obviously reduced, which indicates that the profiles obtained by the joint inversion of the O-wave and X- wave are closer to the real electron density profile.

Geomagnetic Field Variations along the African Geomagnetic Equator During Recovery Phases of 5th July 2011 and 16th July 2012 Geomagnetic Storms

Geomagnetic Field Variations along the African Geomagnetic Equator During Recovery Phases of 5th July 2011 and 16th July 2012 Geomagnetic Storms

An egg case study: Chronic exposure to AC electromagnetic fields results in hyperactivity in thornback ray (Raja clavata L.) embryos.

Subsea power cables, required for offshore generated wind power transport, emit electromagnetic fields (EMFs) into the marine environment. EMFs also occur naturally, resulting from biotic (animals) and abiotic (geomagnetic field) sources. Skate and oviparous shark embryos in the egg can sense EMF from predators and respond by reducing their normal movement ('freezing response') to prevent detection and subsequent predation. When nursery areas overlap with power cables, embryos will be exposed to varying levels of anthropogenic EMFs and effects thereof on embryonic development is currently understudied. Here, we present behavioral responses of thornback ray (Raja clavata) embryos to varying field-related EMF levels (1.8-4.6μT) generated by alternating current throughout embryogenesis (∼20 weeks). Chronically exposed individuals were overall more active, including 33% more tail undulations and 150% increased body movements, compared to non-exposed individuals. This increased activity suggests that eggs exposed to EMFs generated by subsea power cables might be at risk of increased predation. We found no indications of reduced health or survival after hatching, or changes in development time or biometry. Effects on subsequent life stages cannot be excluded, follow-up studies should observe hatchling development. We did not observe an increase in freezing response resulting from EMF change as described by other researchers who used different types and intensities of EMF cues. We recommend that different species, along with DC exposure, should be studied to gain a more complete insight into the potential effects of EMF exposure during embryogenesis of these EMF-sensitive species.

Multi‐Source Forecast of Solar Cycle Flare Activity Using the Novel Informer‐Based Models

AbstractSolar flares, the significant indicators of solar activity, have an impact on Earth's satellites and communication systems. Accurate prediction of solar flare events is crucial for mitigating these effects. In this work, we use multiple data sources, including Geostationary Operational Environmental Satellites soft X‐ray flare flux and the solar flare index, to forecast solar flare activity during Solar Cycle 25 (SC25). Our results show that: (a) The north‐south asymmetry of solar flare activity during SC25 is well revealed, and the southern hemisphere is greater than the northern one. (b) The Gnevyshev peaks of chromospheric flare activity are clearly identified and they are deeper than other atmospheric activity indicators. The different timescales of solar flare responses to the geomagnetic and interplanetary magnetic fields may be the cause of the Gnevyshev peaks. (c) Chromospheric flare activity lags behind photospheric sunspot activity, indicating that changes in sunspot activity precede flare events. (d) The activity level of SC25 is influenced by the modulating effect of the Gleissberg Cycle, as supported by geomagnetic precursor indices. These results offer valuable insights into the temporal and spatial distribution of solar flare activity during SC25.

A Continuous 150‐kyr Record of Geomagnetic Field Variations From Lake Chala, Eastern Equatorial Africa

AbstractRecords of geomagnetic field variations from continental Africa are sparse yet provide a key dating tool for low‐latitude paleoclimatic changes. Long‐lived tectonic and crater lakes in eastern tropical Africa potentially provide important, long (>100,000 years, kyrs) and continuous sedimentary records of African monsoonal climate over past glacial and interglacial stages; the environmental backdrop to human evolution and dispersion. Here, notwithstanding its low latitude location, we present a detailed paleomagnetic record from eastern equatorial Africa extracted from the upper ∼129 m of a continuous sediment sequence drilled in Lake Chala (3°S; 37°E), a permanently stratified crater lake near Mt. Kilimanjaro. The high and stable sedimentation rate (∼0.85 m/kyr), lack of compaction and reliable paleomagnetic signal (assessed by paleo‐ and rock magnetic analyses) enabled the production of a new virtual geomagnetic pole (VGP) record for the last ∼150 ka for equatorial Africa. Six magnetic excursions are recorded: Blake 1 and 2, Post‐Blake, Laschamp, Mono Lake and Hilina Pali. This exceptional record provides key information on the recurrence and duration of intervals of Quaternary geomagnetic instability, and independently‐obtained constraints on the Hilina Pali excursion. Our new paleomagnetic record thus provides a reference data set for late‐Quaternary geomagnetic excursions from African sites and a basis for better understanding of the temporal and spatial evolution of Earth's magnetic field. Finally, correlated with a revised geomagnetic instability timescale, these excursions provide a robust, independent age model for the Lake Chala sediment record, critical for correlating its paleoclimate and environmental proxy records to global reference records.