Geomagnetic Field Variations Research Articles

Two archaeomagnetic intensity maxima and rapid directional variation rates during the Early Iron Age observed at Iberian coordinates. Implications on the evolution of the Levantine Iron Age Anomaly

Variations of geomagnetic field in the Iberian Peninsula prior to Late Iron Age times are poorly constrained. Here we report 14 directional and 10 palaeointensity results from an archaeomagnetic study carried out on 17 combustion structures recovered from six archaeological sites in eastern Spain. The studied materials have been dated by archaeological evidences and supported by radiocarbon dates (8th-5th centuries BC). Rock magnetic experiments indicate that the characteristic remanent magnetization is carried by a low coercivity magnetic phase with Curie temperatures of 500-575°C, most likely titanomagnetite/maghemite with low titanium content. Archaeointensity determinations were carried out by using the classical Thellier-Thellier experiment including pTRM-checks and magnetic anisotropy corrections. A new full vector Iberian Paleosecular Variation Curve for the Iron Age is presented. High fluctuation rates on both directions and intensities are observed during the Early Iron times that seems to be related with the Levantine Iron Age Anomaly (LIAA), the most prominent anomaly of the geomagnetic field of the last three millennia. Two intensity maxima were observed at Iberian coordinates, the oldest around 750 BC (associated with easterly declinations of around 23°) and the second 275 yrs later (475 BC) with northerly directions. The related virtual axial dipole moment was up to 14⋅1022 Am2 for the oldest materials (750 BC) and reaching 16⋅1022 Am2 for the materials corresponding to the end of the Early Iron Age.In order to investigate the origin of the unusually high fluctuations of the palaeofield we have developed a new global geomagnetic field reconstruction, the SHAWQ-IronAge model, which is based on a critical revision of the global archeomagnetic and volcanic dataset. The new model provides an improved description of the evolution of the LIAA, which is related to a normal flux patch at the core-mantle boundary (CMB) below Arabian Peninsula clearly observed at around 950 BC. This flux patch expanded towards the north-west, while decreasing in intensity, reaching Iberia at around 750 BC. Around 600-500 BC, it underwent a revival below the European continent after that it seems to vanish in situ.

About this title - Geomagnetic Field Variations in the Past: New Data, Applications and Recent Advances

In the last decades, palaeomagnetic research has provided important information about the past variation of the Earth's magnetic field (EMF) from its origin to the present day. However, questions regarding the origin and evolution of the EMF as well as the frequency and spatial distribution of its variations still remain open to debate. This Special Publication provides new insights into the study of the temporal and spatial evolution of the EMF presenting new data from palaeomagnetic and rock magnetic studies of archaeological materials, sediments and lavas. The papers presented cover a wide range of topics related to archaeology, stratigraphy and climate, including new data from several parts of the world, such as Europe, Africa, Australia, New Zealand, India and the Baltic Sea. This Special Publication aims to present an overview of the most recent secular variation studies and their use to disclose fundamental properties of the EMF evolution.

Geomagnetic field variations in the past: an introduction

Abstract In the last decades, palaeomagnetic research has provided us with a picture of the temporal and spatial behaviour of the Earth's magnetic field (EMF) from its origin up to the present day. Well-dated palaeomagnetic data offer important sources of information about the past variation of the geomagnetic field and have shown that it is characterized by temporal fluctuations such as reversals, excursions and spikes. Despite the advances in our understanding of EMF behaviour, the current dataset is biased towards high and northern latitudes and, therefore, several questions remain open to debate, such as the origin and evolution of the EMF and the frequency and spatial distribution of its variations. This Special Publication focuses on the study of the temporal and spatial evolution of the EMF in the past through new data from palaeomagnetic and rock magnetic studies of archaeological materials, sediments and lavas from Europe, Africa, Australia, New Zealand, India and Baltic Sea, and their applications in archaeology, stratigraphy and climate. This paper summarizes our current knowledge on geomagnetic field variations in the past, open questions and future challenges and gives an overview of the volume's context, which aims to disclose fundamental properties of the Earth's magnetic field evolution.

ШИРОТНАЯ ЗАВИСИМОСТЬ КВАЗИПЕРИОДИЧЕСКИХ ВАРИАЦИЙ ГЕОМАГНИТНОГО ПОЛЯ В ТЕЧЕНИЕ СИЛЬНЕЙШЕЙ ГЕОКОСМИЧЕСКОЙ БУРИ 7—9 СЕНТЯБРЯ 2017 ГОДА

ШИРОТНАЯ ЗАВИСИМОСТЬ КВАЗИПЕРИОДИЧЕСКИХ ВАРИАЦИЙ ГЕОМАГНИТНОГО ПОЛЯ В ТЕЧЕНИЕ СИЛЬНЕЙШЕЙ ГЕОКОСМИЧЕСКОЙ БУРИ 7—9 СЕНТЯБРЯ 2017 ГОДА

Rock-magnetic and archaeomagnetic investigations on archaeological artefacts from Maharashtra, India

Abstract Archaeointensity and rock-magnetic studies were undertaken on 49 baked clay artefacts from four archaeological sites (Ter, Junnar, Nalasopara and Kanheri) in Maharashtra, India. Rock-magnetic properties, including bulk magnetic susceptibility, magnetic remanence and thermomagnetic analysis, indicate the presence of a low-coercivity magnetite in fine (superparamagnetic, single domain) grain-sizes. The ratio of anhysteretic remanent magnetization to saturation isothermal remanent magnetization, the reversible high-temperature susceptibility curves and the 3-axes isothermal remanent magnetization tests also indicate that the artefacts dominantly possess fine-grained magnetic particles, carrying a stable thermoremanent magnetization (TRM). Archaeointensity was estimated using Coe's modified Thellier method corresponding to the linear behaviour of natural remanent magnetization loss and TRM gained plots, which were evaluated with ThellierTool4.0 software. Cooling rate and anisotropy of the TRM corrections were applied and the corrected intensities were used to calculate a mean archaeointensity value for each one of the four sites. The new archaeointensity values were plotted along the existing Indian archaeointensity values derived only from archaeological artefacts, and were compared with the SHA.DIF.14k and ARCH10k.1 global models’ predictions. The present study aims to improve the overall understanding of Indian geomagnetic field variation in the past by providing new high-quality archaeointensity results. However, still more archaeointensity values are required to develop a reliable secular variation curve for India.

Magnetic Field Variations and Dynamics of the Outer Electron Radiation Belt of the Earth’s Magnetosphere in February 2014

The paper presents the results of a comparative analysis of the dynamics of relativistic electron fluxes of the Earth’s outer radiation belt and correspondent ring current and magnetospheric magnetic field variations for February 15–22, 2014, based on experimental data obtained in the radiation belt core aboard Van Allen Probes satellites and in geostationary orbit aboard the GOES-15 satellite. The A2000 paraboloid model of the magnetosphere is used to calculate the contributions of main magnetospheric current systems to the Dst variation. The influence of external factors—solar wind and interplanetary magnetic field—is considered. Comparison of the dynamics of electron fluxes in different orbits and the geomagnetic field variations for February 15‒22, 2014 indicate that the main mechanisms of the evolution of outer electron radiation belt are global processes: (i) outward and inward shifts of the trapped electron population inside the Earth’s magnetosphere due to large-scale variations of the magnetospheric magnetic field during geomagnetic disturbances and (ii) ExB drift of electrons from the magnetotail under the influence of electric and magnetic fields. Local particle acceleration is auxiliary process in the dynamics of radiation belts. The southward orientation of the interplanetary magnetic field is the necessary condition for an increase in the intensity of electron fluxes of the Earth’s outer radiation belt, while the function (–BzVsw) is the key external factor.

On the resolution of regional archaeomagnetism: untangling directional geomagnetic oscillations and data uncertainties using the French archaeomagnetic database for dates between AD 1000 and 1500 as a guide

Abstract A complexity is emphasized in the distribution of French archaeomagnetic directions during the thirteenth and the fourteenth centuries AD. Data uncertainties, and the smoothing introduced when estimating an average secular variation curve, prevent scrutiny of the very nature of this complexity. It might correspond to a directional yaw, the nature of which would be compatible with the recent geomagnetic field evolution as traced by the gufm1 model. In order to emphasize this indeterminacy, a reference secular variation curve was constructed for dates between AD 1000 and 1500, including the yaw in question, and synthetic databases that mimic the accuracy and density characteristics of the true French archaeomagnetic database were considered for some of these. The synthetic curves hence obtained show that the dating accuracy of archaeomagnetic data is the crucial parameter for constructing a detailed secular variation path. The significant impact of the experimental data accuracy is also illustrated. Even more crucial is the fact that the precision of the data dating required to describe the directional variability over the century timescale largely exceeds the precision of the archaeological dates available for the structures generally studied. This highlights the intrinsic limitation of archaeomagnetism for regional reconstruction of century-scale geomagnetic field variations.

Extreme geomagnetic field variability indicated by Eastern Mediterranean full-vector archaeomagnetic records

The magnetic field of the Earth can exhibit considerable variations at short time scales, even as short as decades. The archaeomagnetic studies of Middle Eastern artefacts (mainly from Israel and Jordan) show evidence for an exceptionally high intensity period from 1050-700 BC which displays two distinct spikes over the Levant, the Levantine Iron Age Anomaly (LIAA). Its exact duration and geographical extent are still poorly known. Despite the wealth of ancient settlements, the extensive cultural heritage and a long history of trade and immigration, the archaeomagnetism of Turkey and Cyprus remains largely unexplored. This study presents a large data set of ancient directions and intensities from seven archaeological sites in the Eastern Mediterranean covering a time span of ∼2000 yrs. The recorded directions from thirteen sets of samples are coherent with our earlier findings, yet show significantly larger swings than existing field models. In particular, we confirm the very large swing in inclination we found earlier, from 1910-1850 BC, that is also captured by the Greek PSV curve, and shallower by more than 10° than predicted by existing field models. Consequently, these models require substantial revision in this region. We were able to determine the archaeointensity from five sets of mud-bricks, from the thirteen attempted, allowing us to provide the full field vector. Furthermore, we present thirty-one new archaeointensity results from potsherds and mud-bricks that considerably enhance existing data, especially when a set of strict selection criteria is applied. Fourteen sets of potsherds from a single site (Tell Atchana) provide the longest sequence recorded so far in Turkey, from 2100 to 1350 BC. We find exceptionally high intensities of 145 and 175 ZAm2 around 700 BC, in well-dated mud-bricks and potsherds from two different locations (Tell Tayinat and Kilise Tepe), supporting extreme geomagnetic field variability in the region. Moreover, these two high intensities confirm the younger spike of the LIAA in Turkey.

English

In this work, monthly means of cosmic ray count rates from two mid latitude (Hermanus and Rome), and two higher latitude (Inuvik and Oulu) neutron monitors (NM) were employed and their variability was compared with geomagnetic stations that are in close proximity to the NMs. The data spans 1966 to 2008 and covers four solar cycles. The difference (CRdiff) between the mean count rate of all days and the mean of the five quietest days for each month was compared with the Dst-related disturbance (Hdiff) derived from the nearby geomagnetic stations. Zeroth- and First-correlation between the cosmic ray parameters and geomagnetic parameters was performed to ascertain statistical association and test for spurious association. The present results show that solar activity is generally strongly correlated (>0.75) with mean strength of GCR count rate and geomagnetic field during individual solar cycles. The correlation between mean strength of cosmic ray intensity and geomagnetic field strength is spurious and is basically moderated by the solar activity. The signature of convection driven disturbances at high latitude geomagnetic stations was evident during the declining phase of the solar cycles close to the solar minimums. The absence of this feature in the slow-time varying cosmic ray count rates in all stations and in the mid latitude geomagnetic stations suggests that the local geomagnetic disturbance do not play a significant role in modulating the cosmic ray flux. Key words: Geomagnetic field variability, solar activity, galactic cosmic rays, cosmic ray modulation.

Fine structure of substorm and geomagnetically induced currents

The rapid changes dB/dt of the Earth’s magnetic field due to substorms can excite large geomagnetically-induced currents (GICs) that can have harmful effects on technological systems. This paper presents an analysis of the characteristics of dB/dt enhancements observed in Fennoscandia using data from the IMAGE magnetometer chain along a geomagnetic longitude of 110 o . The abrupt geomagnetic field variations may be associated with the substorm onsets, isolated magnetic impulsive events (MIEs), and quasi-periodic series of MIEs, known as Ps6 pulsations (periods 5-15 min). For a detailed examination of the latitudinal structure of dB/dt enhancements and their association with the auroral oval boundaries we applied the technique of magnetic keograms. This simple technique helps to visualize and characterize the fine structure of substorm, namely the location in time and latitude of dB/dt enhancements. The location of the auroral oval boundaries has been estimated with the OVATION-prime model. Among the different types of impulsive disturbances investigated auroral substorm onset provides the largest GICs (few tens of A). Isolated nightside MIEs are also effective in the excitation of GICs (>10 A). Ps6 pulsations are effective in the excitation of GICs with magnitude about 20 A and even higher. Monochromatic Pc5 pulsations are capable to induce noticeable GICs, up to ~13 A. Large localized disturbances on short timescales are the actual drivers of GICs, and they may be imagined like geomagnetic “strokes” during magnetospheric “thunderstorms”.

New paleomagnetic results from the ca. 1.68–1.63 Ga mafic dyke swarms in Western Shandong Province, Eastern China: Implications for the reconstruction of the Columbia supercontinent

The existence of Paleo-Mesoproterozoic supercontinent Columbia (aka Nuna) was established decades ago, but the position of North China Craton within Columbia is still highly debated due to the paucity of available high-quality paleomagnetic and reliable geological constraints. Precise geochronological dating of extensive Mesoproterozoic mafic dyke swarms in Western Shandong Province (also named the Luxi area), China reveals two phases of dyke emplacement at ~1.68 Ga and ~1.63 Ga. In this paper, we report new paleomagnetic and rock magnetic results obtained from approximate 160 samples (16 sites) collected from these two phases of mafic dyke swarms in the Luxi area with the aim of pinpointing the location of North China Craton within Columbia supercontinent in this time interval. Rock magnetic experiments confirm that either magnetite or titanomagnetite is the main magnetic carrier in these dykes. Stepwise thermal demagnetization revealed two paleomagnetic poles. For the ~1.63 Ga dykes, normal and reversed high-temperature remanent magnetization directions yield a mean direction (D/I) of 86.1°/53.5° (κ = 43.3, α95 = 7.9°, N = 9). These directions pass a reversal test and are interpreted as primary remanences. The corresponding paleomagnetic pole is calculated at 20.8°N, 182.5°E (κ = 28.3, A95 = 8.3°, N = 9). This pole passes the examination of secular variation of geomagnetic field (Deenen et al., 2011, 2014). It fulfills a Van der Voo (1990) value Q = 6 and is therefore suggested to be a ‘key’ pole demarcating the Precambrian North China Craton. For the ~1.68 Ga dykes, only the normal directions are isolated with a mean direction (D/I) of 89.1°/47.1° (κ = 35.0, α95 = 13.1°, N = 5) with a corresponding paleomagnetic pole of 17.8°N, 184.9°E (κ = 29.6, A95 = 14.3°, N = 5). This pole passes the examination of secular variation of geomagnetic field. Finally we select the ~1.63 Ga high-quantity paleomagnetic pole in order to depict a more detailed apparent pole wander path (APWP) to compare with the other major Precambrian cratons. Combined with other geological evidence, our reconstruction scenario supports the spatio-temporal connection between the Baltica, North Australian Craton and North China Craton.

Solar-Terrestrial Cycles in the Climatic and Geophysical Properties of Crimea

Analysis of the time series of climatic characteristics of the Crimean peninsula for the period of 19832-2005 showed an enhanced growth (compared to other points of the Crimea) of the insolation of the Earth’s surface at Kara-Dag and an anomalous temperature decrease of the Earth’s surface at the Cape Fonar. The parameters of the geomagnetic field of the Kara-Dag mount were estimated. To derive the geomagnetic field variations in Crimea, the IGRF-12 online calculator was used. Regular oscillations were found in the analyzed time series, whose periods coincide with the solar-terrestrial cycles. The coherence functions were calculated and the periods of coherent variations were determined. As a result of the analysis of corrections to the vertical deformations of the Earth’s surface, a seasonal component was selected at Katsiveli and its parameters were calculated.

Preliminary results of simultaneous recording of auroral and geomagnetic pulsations at the ISTP SB RAS station Istok

The paper presents the results on first synchronous observations of variations in auroral luminosity and geomagnetic field, made with high temporal resolution at the ISTP SB RAS high-latitude station Istok (70° N, 88° E) in September–December 2018. Auroras were recorded with all-sky camera, pulsations in the auroras were recorded by a photometer in four spectral ranges with silicon photomultipliers. Continuous monitoring of geomagnetic pulsations was performed using a LEMI-30 three-component induction magnetometer.
 Both synchronous bursts of auroras and magnetic field pulsations, as well as disturbances of auroras, not accompanied by disturbances in the geomagnetic field, were observed. We note that the photometer clearly recorded short-period (~20 min) variations in in auroral luminosity. At the same time, some instability of the photometer signal level occurred at sufficiently long time intervals.
 In the photometer data, there are powerful signal bursts, probably of a hardware nature. Nevertheless, the temporary distribution analysis of the registration moments (registration frequency) of signal bursts indicates the possible dependence of the burst registration frequency on the geomagnetic activity level.

Предварительные результаты синхронной регистрации авроральных и геомагнитных пульсаций на станции «Исток» ИСЗФ СО РАН

The paper presents the results on first synchronous observations of variations in auroral luminosity and geomagnetic field, made with high temporal resolution at the ISTP SB RAS high-latitude station Istok (70° N, 88° E) in September–December 2018. Auroras were recorded with all-sky camera, pulsations in the auroras were recorded by a photometer in four spectral ranges with silicon photomultipliers. Continuous monitoring of geomagnetic pulsations was performed using a LEMI-30 three-component induction magnetometer.
 Both synchronous bursts of auroras and magnetic field pulsations, as well as disturbances of auroras, not accompanied by disturbances in the geomagnetic field, were observed. We note that the photometer clearly recorded short-period (~20 min) variations in in auroral luminosity. At the same time, some instability of the photometer signal level occurred at sufficiently long time intervals.
 In the photometer data, there are powerful signal bursts, probably of a hardware nature. Nevertheless, the temporary distribution analysis of the registration moments (registration frequency) of signal bursts indicates the possible dependence of the burst registration frequency on the geomagnetic activity level.

Комплексний магнітоваріаційний та тектономагнітний моніторинг сучасної геодинаміки західного схилу Антарктичного півострова

Aim – investigations of effectiveness and information value of tectonomagnetic and magnetic-variations monitoring complex to study the recent geodynamics of Antarctic Peninsula in the location of Akademik Vernadsky station. Methodology. The methodology provides long-term magnetic variations observations on the Akademik Vernadsky station. On the base of observations electromagnetic induction vector components (Wise vector) are processing in the range 2.5—60 min. Series of this parameters temporal variations are developing. Tectonomagnetic observations are performed on the stationary network of observational points on the Antarctic geodynamic polygon and then, tectonomagnetic anomalies (increasing of a local magnetic field among observational epochs-total magnetic field vector module) is defined. The nature of tectonomagnetic anomalies usually is connected with variations of tectonic tensions. Compounding of magnetic variations and tectonomagnetic observations allows to upgrade certainty of tectonophysic interpretation of geophysical and geological data for investigations of Antarctic Peninsula recent geodynamics. Results. The results of tectonomagnetic and magnetic variations observations on the Akademik Vernadsky station in the location of Antarctic tectonomagnetic polygon during 1998—2017 yrs. were analyzed and generalized. Temporal variations of Wise electromagnetic induction vectors and local geomagnetic field variations were investigated. Anomalous effects in tectonomagnetic variations and Wise vectors temporal variations, caused by seismotectonic processes in the region’s lithosphere were defined. Comparative analyses of tectonomagnetic and magnetic variations data was done. Also was justified possibility their complex for monitoring of recent seismotectonic processes in the location of Akademik Vernadsky station. Conclusions. Complex analyses of long-term tectonomagnetic field and magnetic variations parameters on the Akademik Vernadsky station was done. Correlation between tectonomagnetic effects on the Antarctic geodynamic polygon and anomalous effects in Wise vectors temporal series was defined. Such complex of tectonomagnetic and magnetic variations monitoring is organic and allows to obtain reliable information about Antarctic Peninsula geodynamics in connection with seismic and other geophysical methods.

Features of the magnetic disturbance on September 7–8, 2017 by geophysical data

The main feature of the geomagnetic disturbance which occurred on September 7–8, 2017, was that it consisted of two consecutive magnetic storms separated in time by ∼13 h. It was of interest to reveal its particular features, characteristics and geomagnetic field variations during both storms and the influence they had on the ionosphere. The results are as follows. The character of the development of the first storm and its impact on the Earth’s magnetosphere and ionosphere are significantly different from the character of the development and impact of the second storm. There are prominent differences in the geomagnetic field variations at different longitudes along the same latitude sector. The asymmetry of the dayside and nightside effects was revealed. The variations of the riometer absorption level, critical frequencies of the ionosphere and Total Electron Content in each considered observation point corresponded to the variations of the magnetic field at this point.

Analysis of the hypothesis of a giant gaussian process as a means for describing secular variations of the geomagnetic field vector

The consistency of the empirical data on paleointensity and paleoinclinations contained in the BOROKPINT paleointensity world database with the Geocentric Axial Dipole (GAD) hypothesis and Giant Gaussian Process (GGP) model describing the geomagnetic field variations in the Brunhes epoch is tested. The calculations are based on the geomagnetic field potential representation by the sum of spherical functions of spatial coordinates with random coefficients, enabling computer simulation of the data with the given statistical characteristics of the coefficients. The estimates show that the Kolmogorov–Smirnov and Anderson–Darling tests reject the GAD hypothesis in its canonical form. The extension of GAD to GGD with nonzero time-average quadrupole and octupole terms makes the paleointensity and paleoinclination data to comply with GGP model realizations; however, these models are mutually exclusive because of mutual inconsistency of their parameters. Testing the paleoinclination data against GDP model shows that a small correction to the purely dipole component of the geomagnetic field should be introduced. At the same time, the paleointensity data analysis suggests that these data highly probably agree with GGP models with a high quadrupole contribution making up 1/3 of the dipole coefficient, which is strongly at odds with the parameters of the model corresponding to paleoinclination data. This inconsistency is most likely to be due to the artifacts associated with incorrect paleointensity determinations; however, this interpretation does not explain the causes of the strong latitudinal dependence of the intensity of the Virtual Axial Dipole Moment (VADM) which follows from the empirical data.

Cardiovascular response as a marker of environmental stress caused by variations in geomagnetic field and local weather

We report the results of a physiological study that include ECG analysis, capillary blood velocity (CBV) data, and blood pressure (BP) measurements obtained under conditions of modified external magnetic field (MF). Each of eight volunteers was sequentially exposed to MFs of three different types for 22 h. A Helmholtz-like MF exposure system was used. The system was specially designed for long-term exposures of human beings to static and low frequency MFs. The MF of the first type reproduced an initially recorded geomagnetic storm (GS). The MF inductions of the other two types were about 55 and 49 μT, which corresponded to the natural local magnetic background and a slightly decreased MF, respectively. In all three cases, the environmental magnetic fluctuations were suppressed by the active Helmholtz system. The variability of RR intervals was considered as a key indicator of cardiovascular response to the MFs and weather conditions. A time-frequency representation (TFR) and a frequency-frequency representation (FFR) were used for processing of the time series of RR intervals. It turned out that the transformation to TFR makes it possible to obtain the characteristic matrix of RR intervals; such a matrix can be used as a subject identifier. FFR was used to calculate correlations of RR intervals with the components of the MFs. The averaged correlation coefficients of RR intervals with the Bx and By components appeared significantly higher (p < 0.001) during the Storm mode in comparison with control. Thus, it is shown that artificial geomagnetic storm can cause a detectable cardiovascular response.

Статистические взаимосвязи вариаций геомагнитного поля, аврорального электроджета и геоиндуцированных токов

Using observations from the IMAGE magnetic observatories and the station for recording geomagnetically induced currents (GIC) in the electric transmission line in 2015, we examine relationships between geomagnetic field and GIC variations. The GIC intensity is highly correlated (R&gt;0.7) with the field variability |dB/dt| and closely correlated with variations in the time derivatives of X and Y components. Daily variations in the mean geomagnetic field variability |dB/dt| and GIC intensity have a wide night maximum, associated with the electrojet, and a wide morning maximum, presumably caused by intense Pc5–Pi3 geomagnetic pulsations. We have constructed a regression linear model to estimate GIC from the time derivative of the geomagnetic field and AE index. Statistical distributions of the probability density of the AE index, geomagnetic field derivative, and GIC correspond to the log-normal law. The constructed distributions are used to evaluate the probabilities of extreme values of GIC and |dB/dt|.

Statistical relationships between variations of the geomagnetic field, auroral electrojet, and geomagnetically induced currents

Using observations from the IMAGE magnetic observatories and the station for recording geomagnetically induced currents (GIC) in the electric transmission line in 2015, we examine relationships between geomagnetic field and GIC variations. The GIC intensity is highly correlated (R&gt;0.7) with the field variability |dB/dt| and closely correlated with variations in the time derivatives of X and Y components. Daily variations in the mean geomagnetic field variability |dB/dt| and GIC intensity have a wide night maximum, associated with the electrojet, and a wide morning maximum, presumably caused by intense Pc5–Pi3 geomagnetic pulsations. We have constructed a regression linear model to estimate GIC from the time derivative of the geomagnetic field and AE index. Statistical distributions of the probability density of the AE index, geomagnetic field derivative, and GIC correspond to the log-normal law. The constructed distributions are used to evaluate the probabilities of extreme values of GIC and |dB/dt|.