Geomagnetic Variations Research Articles

Persistent shallow magnetic inclination in the past 5 million years with implications for regional tectonics in the Philippines

Despite the growing knowledge on geomagnetic paleosecular variations, the region around the Philippine archipelago remains to be a huge data gap in this regard. This work looked into rock magnetic information from <5 Ma volcanic rocks of Luzon Island to provide data for the statistical characterization of the time-averaged field in the region.A total of 21 sites with ages from 1 ka to 4.3 Ma yielded 13 normal, 7 reversed, and 1 intermediate polarity dataset. These were aggregated with previously published work to form a combined dataset of 59 normal + reversed sites with a mean virtual geomagnetic pole at 321.1°E and 83.7°N with α95 = 3.4, and an angular standard deviation of about 14.6°. This amount of scatter is slightly larger than that predicted by Model G but relatively comparable with other near-equatorial regions such as Java and Ecuador. This work is a first examination of paleomagnetic data from the Philippines in relation to the long-term behavior of the magnetic field in this part of Southeast Asia. The long-ranging shallow inclination observed may also have implications on how paleomagnetic data are interpreted for tectonic studies in the region.

MEDIUM-TERM OSCILLATIONS OF THE SOLAR ACTIVITY

In addition to the well-known 11-year cycle, longer and shorter characteristic periods can be isolated in variations of the parameters of helio-geophysical activity. Periods of about 36 and 60 years were revealed in variations of the geomagnetic activity and an approximately 60-year periodicity, in the evolution of correlation between the pressure in the lower atmosphere and the solar activity. Similar periods are observed in the cyclonic activity. Such periods in the parameters of the solar activity are difficult to identify because of a limited database available; however, they are clearly visible in variations of the asymmetry of the sunspot activity in the northern and southern solar hemispheres. In geomagnetic variations, one can also isolate oscillations with the characteristic periods of 5-6 years (QSO) and 2-3 years (QBO). We have considered 5-6-year periodicities (about half the main cycle) observed in variations of the sunspot numbers and the intensity of the dipole component of the solar magnetic field. A comparison with different magnetic dynamo models allowed us to determine the possible origin of these oscillations. A similar result can be reproduced in a dynamo model with nonlinear parameter variations. In this case, the activity cycle turns out to be anharmonic and contains other periodicities in addition to the main one. As a result of the study, we conclude that the 5-6-year activity variations are related to the processes of nonlinear saturation of the dynamo in the solar interior. Quasi-biennial oscillations are actually separate pulses related little to each other. Therefore, the methods of the spectral analysis do not reveal them over large time intervals. They are a direct product of local fields, are generated in the near-surface layers, and are reliably recorded only in the epochs of high solar activity.

Evidence of Correlation between High Frequency Geomagnetic Variations and Seismicity in the Caribbean

An analysis between the hourly distribution of earthquakes in three areas of the Caribbean and the high-frequency variations of the geomagnetic field is presented. The number of earthquakes selected for each zone is between 10,000 and 43,000, which guarantees a statistically significant distribution. The hourly distributions of seismicity in all areas show a bay-shape distribution with a significant increase in the number of earthquakes at night, from 11 PM to 5 AM. For example, in eastern Cuba 36.7% of earthquakes occur at that time, representing 11.7% over 25% in the absence of any time preference. Geomagnetic disturbances were compiled from several years to be able to make a statistically significant hourly distribution of their occurrence, being determined by sudden changes in the magnetic field at a short period of 1 minute. In this sense, geomagnetic data were processed between the years 2011-2016, recorded by the geostationary satellite GOES13 and the magnetic ground station SJG in San Juan, Puerto Rico. The result shows a significant correlation between hourly earthquakes distribution and high-frequency geomagnetic variations. The time-varying conductivity response of Earth’s interior also correlates with seismicity. The theory behind this correlation could be related to the piezoelectric phenomena and the electromagnetic force induced when the magnetic field is disturbed.

Response of atmospheric carbon dioxide to the secular variation of weakening geomagnetic field in whole atmosphere simulations

Responses of atmospheric carbon dioxide (CO₂) density to geomagnetic secular variation are investigated using the Whole Atmosphere Community Climate Model-eXtended (WACCM-X). Our ensemble simulations show that CO₂ volume mixing ratios (VMRs) increase at high latitudes and decrease at mid and low latitudes by several ppmv in response to a 50% weakening of the geomagnetic field. Statistically significant changes in CO₂ are mainly found above ~90 km altitude and primarily redetermine the energy budget at ~100–110 km. Our analysis of transformed Eulerian mean (TEM) circulation found that CO₂ change is caused by enhanced upwelling at high latitudes and downwelling at mid and low latitudes as a result of increased Joule heating. We further analyzed the atmospheric CO₂ response to realistic geomagnetic weakening between 1978 and 2013, and found increasing (decreasing) CO₂ VMRs at high latitudes (mid and low latitudes) accordingly. For the first time, our simulation results demonstrate that the impact of geomagnetic variation on atmospheric CO₂ distribution is noticeable on a time scale of decades.

LONG-TERM TRENDS IN COSMIC RAYS AND GEOMAGNETIC FIELD SECULAR VARIATIONS

Cosmic rays are modulated by solar and geomagnetic activity. In addition, the flux that arrives to the Earth is sensitive to the inner geomagnetic field through its effect on the geomagnetic cutoff rigidity, Rc. This field has been decaying globally at a rate of ~5% per century from at least 1840. However, due to its configuration and non-uniform trend around the globe, its secular variation during the last decades has induced negative and positive Rc trends depending on location. In the present work, the database from the World Data Center for Cosmic Rays (WDCCR) is used to analyze long-term trend variations linked to geomagnetic secular variations. This database includes more than 100 stations covering, some of them, almost seven decades since the 1950’s. Those stations spanning more than 20 years of data are selected for the present study in order to adequately filter solar activity effects.

Modeling Geomagnetic Interference on Railway Signaling Track Circuits

AbstractMisoperation of railway signaling during geomagnetic disturbances has occurred in a number of countries. Railway signals are activated by track circuits that detect the presence of a train in a particular rail section, but geomagnetically induced electric fields can interfere with the track circuit operation, causing the wrong signal to be displayed. This paper develops a new model for track circuit operation that includes the induced geoelectric fields produced by geomagnetic field variations. Rails are modeled as transmission lines with series impedance given by the rail resistance and parallel admittance determined by the current leakage from the rail through the ballast to ground. The transmission line model is then converted into an equivalent‐pi circuit for each rail and these are combined with the track circuit power and relay components to form a nodal admittance network for the track circuit. This is used to examine the effect of induced geoelectric fields on track circuit operation. First, an individual track circuit is examined and it is shown how the length, between insulating rail joints, of the individual rails influences the geomagnetic interference voltage produced across the track circuit relay. Then a series of track circuits is considered: A general solution is developed and then the conditions are identified that allow this to be reduced to a simpler solution considering each track circuit individually. This modeling provides insight into the conditions that produce signaling problems and provides the tools to assess the geomagnetic hazard to railway signaling.

First Estimations of Geomagnetically Induced Currents in the South of Portugal

AbstractGeomagnetic storms induce electric fields in the conducting Earth, which are the source of geomagnetically induced currents (GICs) in grounded power lines. In this study, we compute time‐varying geoelectric fields induced in the southern region of the Portuguese mainland at the time of the strongest geomagnetic storms during solar cycle 24, using a plane‐wave approximation. The driving geomagnetic storm signals are obtained from series recorded at the Coimbra magnetic observatory. Magnetotelluric impedance tensors used to compute the induced electric field are obtained using a conductivity model that takes into account general features of the local lithology and the proximity to the sea. The first GIC simulations for Portugal are presented, using data from the national high voltage power network. Starting with an a priori standard uniform electric field to compute electromotive forces, we first assess the susceptibility of the power system network given only its topology and resistance parameters. For real storms, we report (i) the clustering of the horizontal geomagnetic time variation around the northwest‐southeast direction, (ii) the simulation of the effect of the western and southern coastlines of the territory over the induced electric field, and (iii) the spotting of the substations most sensitive to storms in the studied region.

Statistics of large impulsive magnetic events in the auroral zone

Impulsive geomagnetic variations, latitudinally localized to the auroral zone, have been observed from 2015 to 2020. These impulsive events have been observed mostly in the pre-midnight sector as upward vertical perturbations. Diurnal variations in geomagnetically-triggered harmonic distortion events observed in Hydro-Québec’s Système de Mesure de Décalage Angulaire (SMDA) synchrophasor measurement system found to have a peak in the number of events around midnight. This was similar to diurnal rates of negative Bz geomagnetic impulsive events observed at nearby auroral zone magnetometers. Superposed epoch analysis demonstrates the impulses are regularly associated with increases in harmonic distortion observed at a nearby substation transformer. These large impulsive vertical geomagnetic perturbations appear to be local vortical ionospheric disturbances.

On the Geomagnetic Variations Observed on the Earth’s Surface in the Period Range of Planetary Waves

On the Geomagnetic Variations Observed on the Earth’s Surface in the Period Range of Planetary Waves

Comparison of GPS TEC with IRI models of 2007, 2012, AND 1 2016 over Sukkur, Pakistan

The international reference ionosphere (IRI) models have been widely used for correcting the ionospheric scintillations at different altitude levels. An evaluation on the performance of VTEC correction from IRI models (version 2007, 2012 and 2016) over Sukkur, Pakistan (27.71º N, 68.85º E) is presented in this work. Total Electron Content (TEC) from IRI models and GPS in 2019 over Sukkur region are compared. The main aim of this comparative analysis is to improve the VTEC in low latitude Sukkur, Pakistan. Moreover, this study will also help us to identify the credible IRI model for the correction of Global Positioning System (GPS) signal in low latitude region in future. The development of more accurate TEC finds useful applications in enhancing the extent to which ionospheric influences on radio signals are corrected. VTEC from GPS and IRI models are collected between May 1, 2019 and May 3, 2019. Additionally, Dst and Kp data are also compared in this work to estimate the geomagnetic storm variations. This study shows a good correlation of 0.83 between VTEC of GPS and IRI 2016. Furthermore, a correlation of 0.82 and 0.78 is also recorded for IRI 2012 and IRI 2007 respectively, with VTEC of GPS. The IRI TEC predictions and GPS-TEC measurements for the studied days reveal the potential of IRI model as a good candidate over Pakistan.

The Electric Field Detector on Board the China Seismo Electromagnetic Satellite—In-Orbit Results and Validation

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.

ПРИМЕНЕНИЕ МЕТОДА НАИБОЛЬШИХ ВКЛАДОВ В ТЕХНИКЕ ИНВЕРСИИ МАГНИТОГРАММ

Fundamentals of the spherical harmonic analysis (SHA) of the geomagnetic field were created by Gauss. They acquired the classical Chapman — Schmidt form in the first half of the XXth century. The SHA method was actively developed for domestic geomagnetology by IZMIRAN, and then, since the start of the space age, by ISTP SB RAS, where SHA became the basis for a comprehensive method of MIT (magnetogram inversion technique). SHA solves the inverse problem of potential theory and calculates sources of geomagnetic field variations (GFV) - internal and external electric currents. The SHA algorithm forms a system of linear equations (SLE), which consists of 3K equations (three components of the geomagnetic field, K is the number of ground magnetic stations). Small changes in the left and (or) right side of such SLE can lead to a significant change in unknown variables. As a result, two consecutive instants of time with almost identical GFV are approximated by significantly different SHA coefficients. This contradicts both logic and real observations of the geomagnetic field. The inherent error of magnetometers, as well as the method for determining GFV, also entails the instability of SLE solution. To solve such SLEs optimally, the method of maximum contribution (MMC) was developed at ISTP SB RAS half a century ago. This paper presents basics of the original method and proposes a number of its modifications that increase the accuracy and (or) speed of solving the SLEs. The advantage of MMC over other popular methods is shown, especially for the Southern Hemisphere of Earth.

APPLYING THE METHOD OF MAXIMUM CONTRIBUTIONS TO THE MAGNETOGRAM INVERSION TECHNIQUE

Fundamentals of the spherical harmonic analysis (SHA) of the geomagnetic field were created by Gauss. They acquired the classical Chapman — Schmidt form in the first half of the XXth century. The SHA method was actively developed for domestic geomagnetology by IZMIRAN, and then, since the start of the space age, by ISTP SB RAS, where SHA became the basis for a comprehensive method of MIT (magnetogram inversion technique). SHA solves the inverse problem of potential theory and calculates sources of geomagnetic field variations (GFV) - internal and external electric currents. The SHA algorithm forms a system of linear equations (SLE), which consists of 3K equations (three components of the geomagnetic field, K is the number of ground magnetic stations). Small changes in the left and (or) right side of such SLE can lead to a significant change in unknown variables. As a result, two consecutive instants of time with almost identical GFV are approximated by significantly different SHA coefficients. This contradicts both logic and real observations of the geomagnetic field. The inherent error of magnetometers, as well as the method for determining GFV, also entails the instability of SLE solution. To solve such SLEs optimally, the method of maximum contribution (MMC) was developed at ISTP SB RAS half a century ago. This paper presents basics of the original method and proposes a number of its modifications that increase the accuracy and (or) speed of solving the SLEs. The advantage of MMC over other popular methods is shown, especially for the Southern Hemisphere of Earth.

GRACE—Gravity Data for Understanding the Deep Earth’s Interior

While the main causes of the temporal gravity variations observed by the Gravity Recovery and Climate Experiment (GRACE) space mission result from water mass redistributions occurring at the surface of the Earth in response to climatic and anthropogenic forces (e.g., changes in land hydrology, ocean mass, and mass of glaciers and ice sheets), solid Earth’s mass redistributions were also recorded by these observations. This is the case, in particular, for the glacial isostatic adjustment (GIA) or the viscous response of the mantle to the last deglaciation. However, it has only recently been shown that the gravity data also contain the signature of flows inside the outer core and their effects on the core–mantle boundary (CMB). Detecting deep Earth’s processes in GRACE observations offers an exciting opportunity to provide additional insight into the dynamics of the core–mantle interface. Here, we present one aspect of the GRACEFUL (GRavimetry, mAgnetism and CorE Flow) project, i.e., the possibility to use gravity field data for understanding the dynamic processes inside the fluid core and core–mantle boundary of the Earth, beside that offered by the geomagnetic field variations.

Paleosecular Variations of the Geomagnetic Field Isolated in Pliocene–Quaternary Sediments of Western Turkmenistan

Akchagyl deposits of Western Turkmenistan were studied in order to identify the spectrum of paleosecular variations in the geomagnetic field in Pliocene–Quaternary sediments. The detrital nature of remanent magnetization is established. The spectra of geomagnetic field variations in the Gauss direct polarity intervals (Zau section) and Matuyam reverse polarity intervals (Issu section) in Western Turkmenistan were studied. The spectrum of secular variations in the geomagnetic field is distinguished, in particular, by periods of 8–10, 25–30, and 45–50 ka. The selected periods are stable throughout the Pleistocene and agree well with the results obtained from corresponding deposits in Armenia and Azerbaijan. It should be noted that the revealed discrete series often differ for different elements of the field and different time intervals.

Characterizing Auroral‐Zone Absorption Based on Global Kp and Regional Geomagnetic Hourly Range Indices

AbstractIncreased ionization in the auroral oval leads to the absorption of high‐frequency radio waves in the auroral zone, or auroral absorption. Auroral absorption is typically characterized by global geomagnetic activity indices, such as the Kp index. In this paper the hourly range of the magnetic field (HR) is examined as an alternative to the 3‐hr Kp index for describing the dynamic and localized features of auroral absorption represented by the hourly range of absorption (HRA). Kp, magnetometer, and riometer data were examined for a 3‐year period for stations spread across typical auroral latitudes. A general linear relationship was shown to exist between Kp and LOG10(HRA) for Kp &lt; 4; for Kp ≥ 4 the correlation was weaker. A stronger linear correlation was demonstrated between LOG10(HRA) and LOG10(HR) for HR &gt; 50 nT, characterized by a correlation coefficient of R = 0.63. Increased variability in the relationship between HRA and Kp was attributed to the following factors: the variability of the magnetic field within the 3‐hr window characterized by the Kp index, which was better represented by a 1‐hr HR; the dependence of the Kp index on subauroral magnetic data, which is not subject to the geomagnetic variations typically experienced within the auroral region; and reduced statistics for Kp &gt; 6.

Modeling the 10,000-Year Geomagnetic Disturbance Scenarios Based on Extreme Value Analysis

Modeling the extreme geomagnetic disturbance (GMD) scenarios is of great significance for risk assessment of the power system. In this letter, we model the 10,000-year GMD scenarios using the extreme value analysis to complement the classical 100-year and 200-year events. The 10,000-year GMD event is required for safety-critical nodes such as the ultra-high voltage (UHV)/extra-high voltage (EHV) substations and nuclear power plants, etc. The return level of geomagnetic variation is estimated using the geomagnetic observations based on extreme value theory, which is then combined with the theoretical upper limit of the disturbance storm time (Dst) index to establish the 10,000-year GMD scenarios. Finally, we present an application example of 10,000-year geomagnetically induced currents (GICs) in the Sanhua UHV power grid.

The Effect of Solar-Wind Turbulence on Magnetospheric Activity

The solar wind is a highly turbulent medium exhibiting scalings of the fluctuations ranging over several decades of scales from the correlation length down to proton and electron gyroradii, thus suggesting a self-similar nature for these fluctuations. During its journey, the solar wind encounters the region of space surrounding Earth dominated by the geomagnetic field which is called magnetosphere. The latter is exposed to the continuous buffeting of the solar wind which determines its characteristic comet-like shape. The solar wind and the magnetosphere interact continously, thus constituting a coupled system, since perturbations in the interplanetary medium cause geomagnetic disturbances. However, strong variations in the geomagnetic field occur even in absence of large solar perturbations. In this case, a major role is attributed to solar wind turbulence as a driver of geomagnetic activity especially at high latitudes. In this review, we report about the state-of-art related to this topic. Since the solar wind and the magnetosphere are both high Reynolds number plasmas, both follow a scale-invariant dynamics and are in a state far from equilibrium. Moreover, the geomagnetic response, although closely related to the changes of the interplanetary magnetic field condition, is also strongly affected by the intrinsic dynamics of the magnetosphere generated by geomagnetic field variations caused by the internal conditions.

GIUSEPPE FOLGHERAITER: THE ITALIAN PIONEER OF ARCHAEOMAGNETISM

ABSTRACT The history of the science of archaeomagnetism conventionally starts in 1600 with the publication of William Gilbert's monumental work De Magnete, but the theoretical basis of this scientific field has to be positioned at the end of the nineteenth century. In Italy at that time, a number of scientists such as Giambattista Beccaria, Macedonio Melloni and Silvestro Gherardi, were working on magnetic field characteristics and their work variously contributed to the early study of Earth and rock magnetism. A major contribution to the birth of paleomagnetism as a science, and archaeomagnetism as a dating technique, was produced by Giuseppe Folgheraiter (1856–1913) by means of his research on the magnetic properties of volcanic deposits and his attempts to date ancient pottery of different epochs based on the magnetic properties of clay materials. Initially, Folgheraiter studied the rock magnetism of the volcanic rocks of Latium where he replicated the findings of Macedonio Melloni, who had studied Vesuvius lavas, and found that volcanic rocks are affected by a permanent magnetization. In addition, Folgheraiter verified the discovery by Filippo Keller of the Punti distinti. Folgheraiter also made the innovative proposal that lightning strongly influences the magnetic properties of lavas resulting in magnetic disorder. The main analytical effort of Folgheraiter at the end of the nineteenth century was dedicated to the study of the variations of magnetic inclination in different epochs as registered in archaeological pottery. He produced archaeomagnetic sets of analyses on 191 samples grouped into 10 epochs, that resulted in the first reconstruction of a geomagnetic secular variation curve (SVC). Even if nowadays the Folgheraiter analytical results have been replaced by more precise measurements, a great portion of the development of modern archaeomagnetic techniques originated with Folgheraiter’s experiments and intuitions. Many of those advances were improved upon only during the first half of the twentieth century by Emile Thellier (1904–1987). Actually, the well-known work by Thellier, resulting in the birth of the Saint Maur archaeomagnetic laboratory at the Institut de Physique du Globe de Paris, had as a starting point the theories and suggestions developed by Giuseppe Folgheraiter. Based on the studies by Thellier, the well-known secular variation curve for France was derived, later to be perfected by Ileana Bucur in 1994.

Reflection of the solar activity Hale cycles on the geomagnetic field secular variations

The effect of dramatic decaying of solar activity in the twentieth cycle on secular variations of the Earth’s geomagnetic field has been investigated. Solar activity decay leads to reduction of the number of magnetic storms on the Earth. During the years of large-scale solar activity negative variations from external sources of the field — circular magnetospheric current, increase, as well as amplitudes of changes of auroral and equatorial ionospheric electrojets. Circular current reduces the horizontal component of the Earth’s magnetic field in low and medium latitudes and increases the vertical component in the high latitudes. In auroral latitudes the intensity of auroral electrojets increases during a magnetic storm. Therefore in more active years average annual absolute values of horizontal component of magnetic field will be smaller at the observatories situated in low and medium latitudes and average annual absolute values of the vertical component of magnetic field will be higher in the high latitudes of the Earth. As far as secular variations are determined as the difference between average annual values of the field, the effect of external sources of the field increases with the growth of solar activity.At the observatories of the northern hemisphere of the Earth (West Europe and North America) decaying of solar activity leads to the increase of average annual values of the field, i.e., to positive secular variations. The effect is maximal in the region of the magnetic pole. The amplitude of the effect decreases with the decrease of the latitude of the observatory. The sign of the effect changes (i.e. negative values of secular variations for the northern hemisphere) at the longitudes 60°Е («Kazan») and 150—160°E («cape Uellen», «Barrov»). Amplitudes of negative secular variations are maximal at the magnetic observatory «Irkutsk». The effect is not observed at the insular observatories as well as the observatories in South America. It is evidently a result of superposition of variations with different signs from the external and internal sources such as variations from the currents in the oceanic flows and the equality by the value of amplitude of secular variations from external and internal sources.