Main Geomagnetic Field Research Articles

Розробка цифрових карт модуля індукції геомагнітного поля для території України

Knowledge of Ukraine`s geomagnetic field is based on magnetic surveys of the geomagnetic field induction module B and its power and angular components, as well as on observations or calculations of their anomalous values. The article describes the methods for constructing a digital map of the induction module of the geomagnetic field B. The map of module B for the epoch of 1969.5 is developed, which is the ground to create the maps of module B and its anomalies ΔB for an arbitrary epoch. The results of the ground absolute magnetic survey of 1969-1972, the analytical model of the main geomagnetic field BIGRF, as well as the map of the anomalous magnetic field on a scale of 1: 1,000,000 were used to construct the map of the geomagnetic field induction module B. The digital map of the module and anomalies of the geomagnetic field induction module B for the 1969.5 epoch was obtained by calculating the correction based on their difference values at the points of the absolute reference network. It was spread by interpolation according to the 1x1km matrix to the entire data array for the territory of Ukraine. The geomagnetic field induction module B for the 2005.5 epoch was calculated by adding to its values in the 1969.5 epoch the calculated values of the field dynamics ВIGRF and the "magnetizing" effect of anomalies of the induction module ΔΔB. The developed map is an approximate representation of the magnetic field modulus, since the amount of remanent magnetization was not taken into account during the calculation, which may cause minor deviations of the calculated and observed field values. The induction module of the geomagnetic field B in the epoch of 1969.5 varies in the range of 46,500÷62,000 nT, and in the epoch of 2005.5 ‒ 47,000÷63000 nT, increasing from the southwest to the northeast of the territory of Ukraine. Its maximum values are observed in the areas of regional and local magnetic anomalies, in particular in the area of the Kryvyi Rih-Kremenchuk anomalous strip and the southeastern edge of the Kursk anomaly. The dynamics of the BIGRF field for the period of 1969.5÷2005.5 is characterized by values from 700 nT in the east of the territory of Ukraine to 950 nT in the west, and the magnitude of the magnetizing effect ΔΔB varies within ±10 nT, reaching maximum values (up to 100-190 nT) in the regions of intense magnetic anomalies. The digital map of the geomagnetic field induction module B, developed in 2005.5, has been verified. This was done by measuring the values of module B in the magnetic observatories of Kyiv, L’viv, and Odesa, as well as in the Repeat Stations of the Ist and IInd classes. The results showed that there was only a small difference (-20 ÷ 40 nT) between the calculated and measured values of modulus B. Their most significant differences are spatially correlated with areas of modern activation of the Earth's crust on the territory of Ukraine and electrical conductivity anomalies.

Developing space-time model of the main geomagnetic field based on satellite data for the epoch 2015–2020

Based on measurements of SWARM satellites, a model of the main geomagnetic field for the 2020 epoch and a model of annual field changes until 2025 were built. These models were included in the international model of the main geomagnetic field IGRF-13. The method of data selection and model calculation is described.

Construction of a Spatiotemporal Model of the Main Geomagnetic Field from Satellite Data for the 2015–2020 Epoch

Construction of a Spatiotemporal Model of the Main Geomagnetic Field from Satellite Data for the 2015–2020 Epoch

Correspondence between Cosmic-Dust-Enriched Sediment Horizons and Geomagnetic Field Excursions

The relationship between spikes in cosmic dust fluxes onto the Earth’s surface (mainly represented by native metal particles) and the behavior of the polarity of the main geomagnetic field has been studied. For this, a search was carried out for horizons of paleodeposits with a high concentration of cosmic dust (exceeding the background concentration by more than an order of magnitude). Such increased concentrations of cosmic dust particles were found in peat deposits corresponding to the Etrussia excursion (2.5–3 ka), as well as in ancient Cretaceous and Paleogene marine deposits. In total, we discovered five horizons with a thickness up to 1 m hosting a high concentration of cosmic dust. Measurements of the paleo‒and petromagnetic parameters of samples selected based on the thickness of sedimentary strata showed that the beginning of accumulation of these horizons coincided with geomagnetic field excursions. In this case, sediment enrichment in dust particles could have lasted somewhat longer than a geomagnetic field excursion. Evidence was obtained that Earth collisions with dense fluxes of cosmic dust could have coincided with short-term disturbances in the polarity of the geomagnetic field, but this had no lasting effect on the geodynamo.

The geomagnetic response to the X-class solar flares of September 2017

This study analyzes the variations in the levels of the Earth's magnetic field and its fluctuations in the range of periods of 1–1000 s that accompanied X-class solar flare on 6, 7, and 10 September 2017. Variations of the main Geomagnetic field (GMF) and the fluctuations in the range of periods 1–1000 s were measured by the magnetometer (located at 49.93°N, 36.95°E). The X9.3-class solar flare (SF) on 6 September 2017 induced substantial decreases in X-, Y-, and Z-component levels (−30 nT, −60 nT, and −15 nT, respectively), i.e., crochet effect. These reductions were restored within approximately 60, 150, and 5 min. Additionally, measurements from a magnetometer-fluxmeter (located at 49.64°N, 36.93°E) revealed a temporary sharp decrease in X- (approximately −3 nT) and Y-component (approximately −6 nT) fluctuations, followed by a subsequent increase/restoration lasting 12–15 min. The X8.2 solar flare that occurred on 10 September induced a minor reduction (<10 nT) in the levels of all local GMF components. Concurrently, it triggered a 1.5- to 2-fold amplification of quasi-sinusoidal oscillations in the Y-component fluctuations, characterized by a period of ∼10–12 min and a duration of ∼60 min. The study also discusses the mechanism of variations in the level of the GMF.

Refined Spatio-Temporal Model of Accelerations of the Main Geomagnetic Field on the Earth’s Surface and Geomagnetic Jerks

Refined Spatio-Temporal Model of Accelerations of the Main Geomagnetic Field on the Earth’s Surface and Geomagnetic Jerks

Refined Spatio-Temporal Model of Accelerations of the Main Geomagnetic Field on the Earth’s Surface and Geomagnetic Jerks

Refined spatial spherical harmonic models of the piecewise constant field of secular geomagneticaccelerations have been constructed based on the concept of geomagnetic jerks. The data of the 189 magneticobservatories operating during the extended period of investigations have been analyzed, assuming that jerksare manifestation of sharp changes in regimes of quasi-stationary magnetohydrodynamic process of generationof geomagnetic secular variations in the high-frequency spectrum range. Qualitative and quantitativeanalyses have been carried out, showing the persistency of models of the current generation, and their consistencywith the acceleration field values obtained from direct observatory observations data. The epochs ofjerks that occurred in the extended time period were refined and it was found that on the global scale theyhave quasi-decadal repeatability, through which it is possible to estimate the time characteristics of regimesof the stationary evolution of the magnetic field of the Earth’s core. An analysis of the results of spherical harmonicmodeling using the maps of the global field of accelerations showed that the origins of all identifiedjerks are of an intraterrestrial character, which also provide the specific features of their morphological structure,as well as the degree of their distribution on the Earth’s surface

Об оценке сейсмотектонического потенциала: практический аспект в связи с геоэкологией

A methodical approach and results of estimating the seismotectonic potential of the region (the maximum possible earthquake magnitude Mmax) based on geomagnetic data are presented – the value of the geomagnetic Z-component in the geocentric solar magnetospheric coordinate system (ZGSM), which can be calculated using the international reference model of the main geomagnetic field IGRF. The expediency of applying such an approach to assessing the seismotectonic potential in areas with weakened seismicity, which may currently be in the long-term seismic quiescence, is shown. This may be especially appropriate when assessing the seismic potential in the case of location of critical strategic structures and other environmentally hazardous facilities in such territories.

Analysis of Global Geomagnetic Main Field Model Order Based on Bayesian Evidence

全球主磁场模型描述了主磁场的时空分布特征。模型的主磁场阶数是构建主磁场模型的关键问题之一。使用贝叶斯推理分析全球主磁场模型，依据贝叶斯证据比较模型阶数，为主磁场的阶数分析提供一种统计依据。利用Swarm卫星磁测数据，估计不同阶数的主磁场模型的证据。结果表明，在1~20的模型阶数中，阶数<i>N</i> = 12具有全局最佳证据。参照Jefrrey’s scale的阈值区间，数据对阶数<i>N</i> = 12的偏好显著优于其他阶数。实验表明，主磁场阶数的证据推理可用于研究主磁场贡献，结果与14阶球谐函数的功率谱分析相匹配。

Analysis of Global Geomagnetic Main Field Model Order Based on Bayesian Evidence

Analysis of Global Geomagnetic Main Field Model Order Based on Bayesian Evidence

Study of the geomagnetic field’s regional gradients in Chinese continent using three-dimensional surface Spline model

We combined domestic ground-based and satellite magnetic measurements to create a regional three-dimensional surface Spline (3DSS) gradient model of the main geomagnetic field over the Chinese continent. To improve the precision of the model, we considered the data gap between the ground and satellite data. We compared and analyzed the results of the Taylor polynomial, surface Spline, and CHAOS-6 (the CHAMP, Ørsted and SAC-C model of Earth’s magnetic field) gradient models. Results showed that the gradients in the south−north and east−west directions of the four models were consistent. The 3DSS model was able to express not only gradients at different altitudes, but also average gradients inside the research area. The two Spline models were able to capture more information on gradient anomalies than were the fitted models. Strong local anomalies were observed in northern Xinjiang, Beijing, and the junction area between Jiangsu and Zhejiang, and the total intensity <italic>F</italic> decreased whereas the altitude increased. The gradient decreased by 21.69% in the south−north direction and increased by 11.78% in the east−west direction. In addition, the altitude gradient turned from negative to positive while the altitude increased. The Spline model and the two fitted models differed mainly in the field sources they expressed and the modeling theory.

Investigation of geomagnetic reference models based on the Iridium^{circledR } constellation

The World Magnetic Model (WMM) is a geomagnetic main field model that is widely used for navigation by governments, industry and the general public. In recent years, the model has been derived using high accuracy magnetometer data from the Swarm mission. This study explores the possibility of developing future WMMs in the post-Swarm era using data from the Iridium satellite constellation. Iridium magnetometers are primarily used for attitude control, so they are not designed to produce the same level of accuracy as magnetic data from scientific missions. Iridium magnetometer errors range from 30 nT quantization to hundreds of nT errors due to spacecraft contamination and calibration uncertainty, whereas Swarm measurements are accurate to about 1 nT. The calibration uncertainty in the Iridium measurements is identified as a major error source, and a method is developed to calibrate the spacecraft measurements using data from a subset of the INTERMAGNET observatory network producing quasi-definitive data on a regular basis. After calibration, the Iridium data produced main field models with approximately 20 nT average error and 40 nT maximum error as compared to the CHAOS-7.2 model. For many scientific and precision navigation applications, highly accurate Swarm-like measurements are still necessary, however, the Iridium-based models were shown to meet the WMM error tolerances, indicating that Iridium is a viable data source for future WMMs.Graphical

A regional geomagnetic field model over Southern Africa derived with harmonic splines from Swarm satellite and ground-based data recorded between 2014 and 2019

A regional harmonic spline geomagnetic main field model, Southern Africa Core Field Model (SACFM-3), is derived from Swarm satellite and ground-based data for the southern African region, in the eastern part of the South Atlantic Anomaly (SAA) where the field intensity continues to decrease. Using SACFM-3 and the global CHAOS-6-×9 model, a detailed study was conducted to shed light on the high spatial and temporal geomagnetic field variations over Southern Africa between 2014 and 2019. The results show a steady decrease of the radial component Z in almost the entire region. In 2019, its rate of decrease in the western part of the region has reached high values, 76 nT/year and 78 nT/year at Tsumeb and Keetmanshoop magnetic observatories, respectively. For some areas in the western part of the region the radial component Z and field intensity F have decreased in strength, from 1.0 to 1.3% and from 0.9 to 1.2%, respectively, between the epochs 2014.5 and 2019.5. There is a noticeable decrease of the field intensity from the south-western coast of South Africa expanding towards the north and eastern regions. The results show that the SAA area is continuing to grow in the region. Abrupt changes in the linear secular variation in 2016 and 2017 are confirmed in the region using ground-based data, and the X component shows an abrupt change in the secular variation in 2018 at four magnetic observatories (Hermanus, Hartebeesthoek, Tsumeb and Keetmanshoop) that needs further investigation. The regional model SACFM-3 reflects to some extent these fast core field variations in the Z component at Hermanus, Hartebeesthoek and Keetmanshoop observatories.Graphical

Direct Comparison of the Tsunami‐Generated Magnetic Field With Sea Level Change for the 2009 Samoa and 2010 Chile Tsunamis

AbstractThe motion of conductive seawater by tsunamis can generate magnetic fields in the presence of the background geomagnetic main field. Previous studies found that, using the tsunami‐generated seafloor magnetic field, it is possible to predict the propagation direction and wave height prior to the actual arrivals of tsunamis. This study correlates the tsunami magnetic field and the tsunami sea level change using observed data and three‐dimensional simulations of the 2009 Samoa and 2010 Chile tsunamis. Our direct comparison of the tsunami observed magnetic field and tsunami sea level change illustrate that the vertical tsunami magnetic component, , arrived earlier than the sea level change. The “initial rise” signal in the observed horizontal tsunami magnetic component, , which was arrived even earlier than also is found by combing the observation with the three‐dimensional simulations. We further examine the precision of conversion of the tsunami magnetic field to the sea level change and find that the magnetic field derived tsunami sea levels are as precise as those obtained from differential pressure gauge data. However, our simulation shows that existing tsunami source models are incompatible with our tsunami magnetic data. Therefore, it is necessary to include magnetic field derived tsunami sea level changes to improve those source models.

Variations in the geomagnetic field that accompanied the 10 June 2021 solar eclipse

Urgency. At present, the existence of the geomagnetic effect of solar eclipses (SEs) is in question. The data presented in the literature are contradictory. Some researchers assert that the amplitude of the north-south component of the main geomagnetic field increases, while others that it decreases. The third group of researchers notes that this amplitude does not change at all, but instead the amplitude of the west-east component shows variations. In some cases, observations confirm the mechanism for the geomagnetic effect caused by disturbances in the Sq current system, while in other cases observations contradict with the mechanism. The difficulties that are encountered in observing the SE geomagnetic effect are caused by the fact that the magnetic field is subjected to the influence of many energy sources. The magnitude of the geomagnetic effect depends not only on the magnitude (phase) of the solar eclipse but also on the state of space weather, geographic coordinates of data acquisition, local time, season, etc. Therefore, the study of the geomagnetic effect from each new solar eclipse remains an urgent problem. The main feature of the 10 June 2021 Solar eclipse is its annularity. The maximum magnitude did not exceed 0.943, and the eclipse obscuration 89%. The aim of this work is to present the results of analysis of variations in the geomagnetic field that were recorded by the INTERMAGNET during the 10 June 2021 SE. Methods and Methodology. To analyze the effects in the main Earth’s magnetic field, the INTERMAGNET data have been utilized. The data have been analyzed from 15 magnetic observatories located between 77.47°-N and 48.17°-N latitude where the maximum phase varied from 0.943 to 0.124. The analysis was performed with 1-min temporal resolution providing a 0.1-nT resolution. To determine spectral content of the quasi-periodic variations, the systems spectral analysis has been used, which combines mutually complementary the short-time Fourier transform, the wavelet transform employing the Morlet wavelet as a basis function, and the Fourier transform in a sliding window with a width adjusted to be equal to a fixed number of harmonic periods. Results. An aperiodic geomagnetic effect of a solar eclipse has been detected and explained; it consists in a decrease by not greater than 30 nT in the level of the north-south component. The effect is explained by a variation in the ionospheric current density in the west-east direction as a result of a decrease in the electron density during the eclipse. A quasi-periodic geomagnetic effect of a solar eclipse has been revealed; it is explained by the generation of atmospheric gravity waves. The wave acts to modulate the ionospheric electric current, as well as to drag the electrons inducing additional quasi-periodic ionospheric current with a period equal to the wave period. The amplitude of the quasi-periodic variations was observed to be a few nanoteslas. The systems spectral analysis provided more precise values of periods of quasi-periodic variations in the geomagnetic field accompanying the solar eclipse, approximately 20 min and 35 min. Conclusions. The aperiodic and quasi-periodic geomagnetic effects are caused by the disturbance (generation) of the ionospheric current.

Amplitude of the magnetic anomaly vector in the interpretation of total-field anomaly at low magnetic latitudes

We propose the use of the amplitude of the magnetic anomaly vector (amplitude data) for qualitative interpretation of large areas at low magnetic latitudes. The amplitude data are weakly dependent on the magnetization direction. Hence, the amplitude data require no prior knowledge of the source magnetization direction. The amplitude data produce maxima over the causative sources, allowing the definition of the horizontal projections of the sources. This characteristic is attractive for interpretation at low magnetic latitudes because at these regions the interpretation of the total-field anomaly is not straightforward. We compute the amplitude data using the equivalent-layer technique to transform the total-field anomaly into the three orthogonal components of the magnetic anomaly vector. We analyze the results of tests in synthetic data simulating a main geomagnetic field at high, mid and low latitudes, with sources ranging from symmetric to elongated forms, including a dipping source. These sources, that give rise to the simulated anomalies, have both induced and strong remanent magnetizations. By comparing the amplitude data with the total gradient, we show that the amplitude data locate the horizontal projections of the sources. Thus, the amplitude data can be used to delineate the boundaries of the sources. We apply both the amplitude data and the total gradient to a real total-field anomaly over a large area of the Amazonian Craton, northern Brazil, located at low magnetic latitudes. The amplitude data show a better performance in delineating geologic bodies that are in agreement with the outcropping intrusions in the geologic map. Moreover, the amplitude data revealed new geologic bodies that were not present in the geologic map. The clear alignment of these new bodies with the outcropping intrusions suggested the continuity of these intrusions in depth. This result is a step forward in understanding this area for which the geology is poorly known. Hence, the amplitude data can provide an apparent-geologic map especially in areas at low latitudes with remanently magnetized bodies.

Geomagnetic Virtual Observatories: monitoring geomagnetic secular variation with the Swarm satellites

We present geomagnetic main field and secular variation time series, at 300 equal-area distributed locations and at 490 km altitude, derived from magnetic field measurements collected by the three Swarm satellites. These Geomagnetic Virtual Observatory (GVO) series provide a convenient means to globally monitor and analyze long-term variations of the geomagnetic field from low-Earth orbit. The series are obtained by robust fits of local Cartesian potential field models to along-track and East–West sums and differences of Swarm satellite data collected within a radius of 700 km of the GVO locations during either 1-monthly or 4-monthly time windows. We describe two GVO data products: (1) ‘Observed Field’ GVO time series, where all observed sources contribute to the estimated values, without any data selection or correction, and (2) ‘Core Field’ GVO time series, where additional data selection is carried out, then de-noising schemes and epoch-by-epoch spherical harmonic analysis are applied to reduce contamination by magnetospheric and ionospheric signals. Secular variation series are provided as annual differences of the Core Field GVOs. We present examples of the resulting Swarm GVO series, assessing their quality through comparisons with ground observatories and geomagnetic field models. In benchmark comparisons with six high-quality mid-to-low latitude ground observatories we find the secular variation of the Core Field GVO field intensities, calculated using annual differences, agrees to an rms of 1.8 nT/yr and 1.2 nT/yr for the 1-monthly and 4-monthly versions, respectively. Regular sampling in space and time, and the availability of data error estimates, makes the GVO series well suited for users wishing to perform data assimilation studies of core dynamics, or to study long-period magnetospheric and ionospheric signals and their induced counterparts. The Swarm GVO time series will be regularly updated, approximately every four months, allowing ready access to the latest secular variation data from the Swarm satellites.

A secular variation candidate model for IGRF-13 based on Swarm data and ensemble inverse geodynamo modelling

This paper describes the design of a candidate secular variation model for the 13th generation of the International Geomagnetic Reference Field. This candidate is based upon the integration of an ensemble of 100 numerical models of the geodynamo between epochs 2019.0 and 2025.0. The only difference between each ensemble member lies in the initial condition that is used for the numerical integration, all other control parameters being fixed. An initial condition is defined as follows: an estimate of the magnetic field and its rate-of-change at the core surface for 2019.0 is obtained from a year (2018.5–2019.5) of vector Swarm data. This estimate (common to all ensemble members) is subject to prior constraints: the statistical properties of the numerical dynamo model for the main geomagnetic field and its secular variation, and prescribed covariances for the other sources. One next considers 100 three-dimensional core states (in terms of flow, buoyancy and magnetic fields) extracted at different discrete times from a dynamo simulation that is not constrained by observations, with the time distance between each state exceeding the dynamo decorrelation time. Each state is adjusted (in three dimensions) in order to take the estimate of the geomagnetic field and its rate-of-change for 2019.0 into account. This methodology provides 100 different initial conditions for subsequent numerical integration of the dynamo model up to epoch 2025.0. Focussing on the 2020.0–2025.0 time window, we use the median average rate-of-change of each Gauss coefficient of the ensemble and its statistics to define the geomagnetic secular variation over that time frame and its uncertainties.

Tsunami-generated magnetic fields have primary and secondary arrivals like seismic waves

A seafloor geomagnetic observatory in the northwest Pacific has provided very long vector geomagnetic time-series. It was found that the time-series include significant magnetic signals generated by a few giant tsunami events including the 2011 Tohoku Tsunami. Here we report that the tsunami-generated magnetic fields consist of the weak but first arriving field, and the strong but second arriving field—similar to the P- and S-waves in seismology. The latter field is a result of coupling between horizontal particle motions of the conductive seawater and the vertical component of the background geomagnetic main field, which have been studied well so far. On the other hand, the former field stems from coupling between vertical particle motions and the horizontal component of the geomagnetic main field parallel to tsunami propagation direction. The former field has been paid less attention because horizontal particle motions are dominant in the Earth’s oceans. It, however, was shown that not only the latter but also the former field is significant especially around the magnetic equator where the vertical component of the background magnetic field vanishes. This implies that global tsunami early warning using tsunami-generated magnetic fields is possible even in the absence of the background vertical geomagnetic component.

Typical Characteristics of the Earth’s Magnetic and Gravity Fields Related to Global and Regional Tectonics

Abstract —We present a summary and analysis of current views on the magnetic and gravity fields of the Earth as a reflection of global and regional tectonic processes. The discussion concerns the probable interconnection between the distribution of the geomagnetic field characteristics, gravity anomalies and the manifestations of mantle plume magmatism as the most remarkable geologic indicator of deep geodynamics. We demonstrate that the distribution of the characteristics of the main geomagnetic field has a qualitative similarity to anomalies of the gravity field. Brief variations of the geomagnetic field are due to high-frequency oscillations in the ionosphere, do not affect the general state of the field, and are useless when considering issues of global tectonics. On the contrary, variations with long periodicities, first of all geomagnetic reversals, can be among the main indicators of the evolution of the geodynamo – the heat mechanism controlling the entire series of global tectonic processes. The frequency of reversals is determined by the intensity of mantle plumes that cause the cooling of the core, increase the convection rate in the asthenosphere, and respectively, the periodic changes in the tectonosphere. We assume the existence of three modes of behavior for this system. The first one corresponds to steady convection, in which reversals are extremely rare or do not happen at all. These episodes – superchrons – compose no more than 20% of the duration of the Phanerozoic. The second mode occurs significantly more often in the geologic history and is characterized by active convection with frequent reversals happening at least once every 5 Myr. Finally, the third mode, which is rare for the Phanerozoic but was probably more prevalent in the early Precambrian, corresponds to hyperactive turbulent convection, when the frequency of reversals reached 20 and possibly more during one million years. Although the demonstrated qualitative similarity in the position of extreme values of the main geomagnetic field, the centers of free air gravity anomalies, and manifestations of large igneous provinces does not yet have a credible explanation, we consider it to be fundamental and requiring special study and detailed elaboration.