Variations In Earth's Magnetic Field Research Articles

Evaluating F2-region long-term trends using the International Reference Ionosphere (IRI) model: is this a feasible approximation for experimental trends?

Abstract. The International Reference Ionosphere (IRI) is a widely used empirical ionospheric model based on observations from a worldwide network of ionospheric stations. Therefore, it would be reasonable to expect it to capture long-term changes in key ionospheric parameters, such as foF2 and hmF2 linked to trend forcings like greenhouse gas increasing concentrations and the Earth's magnetic field secular variation. Despite the numerous reported trends in foF2 and hmF2 derived from experimental data and model results, there are inconsistencies that require continuous refinement of trend estimation methods and regular data updates. This ongoing effort is crucial to address the difficulties posed by the weak signal-to-noise ratio characteristic of ionospheric long-term trends. Furthermore, the experimental verification of these trends remains challenging, primarily due to time and spatial coverage limitations of measured data series. Achieving these needs for accurate detection of long-term trends requires extensive global coverage and high resolution of ionospheric measurements together with long enough periods spanning multiple solar cycles to properly filter out variations of shorter terms than the sought trend. Considering these challenges, IRI-modeled foF2 and hmF2 parameters offer a valuable alternative for assessing trends and obtaining a first approximation of a plausible global picture representative of experimental trends. This work presents these global trend patterns, considering the period 1960–2022 using the IRI-Plas 2020 version, which are consistent with other model predictions. While IRI explicitly takes into account the Earth's magnetic field variations, the increase in the concentrations of greenhouse gases appears indirectly through the Ionospheric Global index (IG) which is derived from ionospheric measurements. F2-region trends induced by the first mechanism should be important only around the magnetic equator at the longitudinal range with the strongest displacement, and it should be negligible out of this region. Conversely, trends induced by the greenhouse effect, which are the controversial ones, should be dominant away from the geomagnetic equator and should globally average to negative values in both cases, i.e., foF2 and hmF2. Effectively, these negative global means are verified by trends based on IRI-Plas, even though not for the correct reasons in the hmF2 case. In addition, a verification was performed for more localized foF2 trend values, considering data from nine mid-latitude stations, and a reasonable level of agreement was observed. It is concluded that the IRI model can be a valuable tool for obtaining preliminary approximations of the Earth's magnetic-field-induced long-term changes in foF2 and hmF2, as well as of experimental trends only in the foF2 case. The latter does not hold for hmF2, even if the trends obtained are close to the expected values.

Influence of Earth magnetic field on animal nervous system evolution

The aim of the present study was to demonstrate the impacts of earth magnetic field (ErMF) on animal nervous system evolution especially electric and histological properties of nerves. We have applied for the first time, as far as we know, a correlation betwen the influence of ErMF and temperature on supraconductor-like behavior in the siatic nerves of four species. Our question point to answer to the a possible link between magnetic change and climate change and to explain in part the possible implication of both parameters in animal nervous system adaptation and evolution. Our results seem to support the existence of a link between ErMF variation and superconductor-like behavior in nerves. The found link does not mean that the ErMF is fully responsible of the histological, electric properties of nerves and climate changes. The data reveal a decrease in nerve resistivity in chameleon and frog, chick and rabbit; showing a superconductor-like behaviour. Analysis of electrical properties demonstrated a clear grade shift at critical temperature (Tc) from poikilotherm (average of ΔT = 11.50) to homeotherm (average of ΔT = 38.00); indicating adaptive nerves changes during evolution confirmed by the increase of Schwann cells number.

Late Holocene paleosecular variation and relative paleointensity records from Lagoa dos Patos (southern Brazil)

Lake and lagoon sediments are important recorders of the Earth's magnetic field variations. However, the Southern Hemisphere, particularly the South American continent, contributes only a small fraction of the global paleosecular variation (PSV) and relative paleointensity data, which hinders a better understanding of the global PSV. Moreover, the scarcity of information on the geomagnetic field in South Brazil for the past few millennia impedes, for example, a detailed analysis of the evolution of the South Atlantic Magnetic Anomaly (SAMA), which encompasses the weakest geomagnetic field on the Earth's surface. Here, we present high-resolution paleomagnetic and rock magnetic data of two cores collected at the lagoon of Lagoa dos Patos, Rio Grande do Sul State, Brazil. Sediment cores from Lagoa dos Patos represent the period from ∼4540 to 3320 cal years BP. Rock magnetic results show the remanent magnetization resides in pseudo single-domain (PSD) magnetite and/or titanomagnetite. Magnetization inclinations and declinations were isolated after alternating field demagnetization (AFD) and principal component analysis (PCA). Mean inclinations are −39,6° and − 38,4° for cores PT-04 and PT-06, respectively. Relative paleointensity results are compatible with geomagnetic field models, implying very promising results in the reconstruction of a reference curve for the region. As there is no PSV and relative paleointensity data for this region in this period, this study helps to elucidate the past field and the presence of SAMA in South America.

A first regional model of the past Earth's magnetic field from Africa for the last 4000 years

The understanding of the Earth's magnetic field variations over time on the African continent is fundamental for several reasons. For instance, the most important feature of the present geomagnetic field, the South Atlantic Anomaly (SAA) characterized by weaker geomagnetic strength values than those expected for their latitudes, may have emerged in South Africa at the beginning of the second millennium CE. Here, we first selected the available volcanic and archaeomagnetic data following a set of three criteria inspired by the FAIR principles. We then built a first regional geomagnetic model for Africa covering the last 4000 years, using a revised version of the spherical cap harmonic (SCH) analysis in 2 dimensions. The new regional model shows, at the Earth's surface, the westward migration of the SAA from the Indian Ocean over Africa since 1100 CE. In addition, the regional model is tested as a paleomagnetic dating tool by re-dating previous archaeomagnetic data from Africa and thus can be used to date other African archeological sites and the numerous active and dormant volcanoes of the East African System. Plain language summaryThe spatial and temporal evolution of the Earth's magnetic (geomagnetic) field is based on direct historical or instrumental data and the indirect information extracted from rocks and archeological artifacts (palaeo- and archaeomagnetic data). While the present field is well sampled at both spatial and temporal domains, this is not the case for the past evolution of the geomagnetic field, where the paleomagnetic data are not globally distributed. There are large areas in the Southern Hemisphere yet to be investigated. However, recent data from Africa enables us the building of the first regional geomagnetic model for the last 4000 years. The new regional model sheds light on the past evolution of the most remarkable feature of the present geomagnetic field, the South Atlantic Anomaly (SAA), showing details of the westward migration of the SAA from the Indian Ocean over Africa since 1100 CE. Moreover, the new model refines the use of paleomagnetism as a dating tool for volcanic units from East African Rift System and for the abundant African archeological sites improving the knowledge of the history of human civilizations.

MagIC as a FAIR Repository for America's Directional Archaeomagnetic Legacy Data

AbstractBeginning in 1964, an academic lineage of Robert DuBois and his students, Daniel Wolfman and Jeffrey Eighmy, developed dedicated United States‐based archaeomagnetic research programs. Collectively, they analyzed over 5,377 archaeomagnetic sites, primarily from North America, dated to less than 2,000 years old. Yet despite their decades of effort, few journal publications resulted. Most of their published results are embedded in archeological reports, often without technical data, which limits the data's accessibility. Furthermore, when published, the results are generally averaged at the site level using statistical conventions different from today's standards, limiting the data's comparability and (re)usability. In 2015, we undertook a salvage archival study to digitize the surviving data and metadata from the scientists' individual estates and emeritus collections. We digitized measurement data from more than 51,000 specimens, reinterpreted them using modern conventions, and uploaded them to the FAIR‐adhering magnetic data repository, earthref.org/MagIC. The reinterpreted site‐level results from the three laboratories are mutually consistent, permitting the individual data sets to be combined and analyzed as single regional entities. Through incorporation into the MagIC repository, these legacy data are now accessible for incorporation into archaeomagnetic and global magnetic field modeling efforts, critical to understanding Earth's magnetic field variation through time. In the Four Corners region of the United States Southwest, this digitized archive advances the development of a new regional paleosecular variation curve used in archaeomagnetic dating. This project highlights both the value and complexities of managing legacy data; the many lessons learned to set a precedent for future paleomagnetic data recovery efforts.

Noise across Olduvai Subchron: Paleomagnetic study of a Pliocene lava succession from Javakheti Highland (Georgia, Lesser Caucasus)

Well-exposed lava sequences with available geochronological information may provide invaluable information on the fine characteristics of the Earth's magnetic field variation. A paleomagnetic study has been performed on twenty Pleistocene age, sub-horizontal lava flows in the Javakheti Highland (Lesser Caucasus). The sequence is formed by calc-alkaline basaltic lavas and is divided by a thin sedimentary layer in its upper part. We obtained two new radiometric ages: an age of 1.93±0.09 Ma for the flows below the sedimentary layer and 1.78±0.11 Ma for the upper part of the sequence. Thermomagnetic susceptibility vs. temperature curves indicate that remanence is carried by ferrimagnetic minerals like magnetite, titanomagnetite or titanomaghemite. Reliable paleomagnetic results could be obtained from all 20 analyzed flows, yielding the following reverse-polarity mean direction for the whole sequence: inclination I =-61.5°and declination D =200.1° (N = 20; α95 =3.1°; k=114). This direction does not agree with the expected one. The discrepancy can be explained by an apparent clockwise 17.1 ± 6.1° vertical-axis rotation. Alternatively, such moderate deviation may be due to some unstable geomagnetic regime or undersampled paleosecular variation. Isotope ages obtained in the present study indicate that the Toloshi sequence was emplaced during the normal-polarity Olduvai subchron, but palaeomagentic results indicate a reverse-polarity magnetization. At the same time, the analysis of virtual geomagnetic pole (VGP) scatter indicates that the Toloshi sequence was probably formed during a short time, insufficient to average paleosecular variation. These results suggest that the Olduvai subchron is probably disrupted by a short reverse-polarity episode.

ВЫСОКОВОЛЬТНЫЙ МОНИТОРИНГ ГЕОМАГНИТНО-ИНДУЦИРОВАННЫХ ТОКОВ

Within the framework of the national project “Digital economy of the Russian Federation” the Ministry of energy of the Russian Federation is implementing the departmental project “unified technical policy – relia-bility of power supply”. The main objectives of the departmental project are aimed at implementing risk-based management, improving the level of reliability of energy supply to consumers. One of the risk factors for pow-er supply systems is a natural phenomenon caused by ionospheric-magnetospheric connections – geomagnetic-induced currents. The proposed method for assessing these risks is based on the registration of higher harmon-ics in high-voltage power lines, which makes it possible to improve the accuracy of diagnostics of geomagnet-ic-induced currents by reducing the influence of the network's own harmonics. The choice of the optimal even harmonic number for diagnostics is theoretically shown and experimentally confirmed. A contactless method for obtaining information about variations of higher harmonic components in high-voltage power lines is pro-posed and tested. The degree of the 6th harmonics correlation in 220 kV power transmission lines of Mutnovskaya Geothermal Power Plant with the Earth's magnetic field variations obtained at the observatory “Paratunka” (Paratunka village, Kamchatsky Krai) was experimentally investigated.

Phenomena preceding major earthquakes interconnected through a physical model

Abstract. The analysis of earthquake time series in a new time domain termed natural time enables the uncovering of hidden properties in time series of complex systems and has been recently employed as the basis of a method to estimate seismic risk. Natural time also enables the determination of the order parameter of seismicity, which is a quantity by means of which one can identify when the system approaches the critical point (the mainshock occurrence is considered the new phase). Applying this analysis, as an example, to the Japanese seismic data from 1 January 1984 until the super-giant M 9 Tōhoku earthquake on 11 March 2011, we find that almost 3 months before its occurrence the entropy change of seismicity under time reversal is minimized on 22 December 2010, which signals an impending major earthquake. On this date the order parameter fluctuations of seismicity exhibit an abrupt increase. This increase is accompanied by various phenomena; e.g., from this date the horizontal GPS azimuths start to become gradually oriented toward the southern direction, while they had random orientation during the preceding period. Two weeks later, a minimum of the order parameter fluctuations of seismicity appears accompanied by anomalous Earth magnetic field variations and by full alignment of the orientations of GPS azimuths southwards leading to the most intense crust uplift. These phenomena are discussed and found to be in accordance with a physical model which seems to explain on a unified basis anomalous precursory changes observed either in ground-based measurements or in satellite data.

Magnetic Mineral Diagenesis in a High Temperature and Deep Methanic Zone in Izu Rear Arc Marine Sediments, Northwest Pacific Ocean

AbstractMagnetic mineral diagenesis is an important process in sediments that is responsible for the partial or total destruction of records of Earth's magnetic field variations and also plays an important part in iron and sulfur cycling. A rock magnetic study has been carried out at International Ocean Discovery Program Expedition 350 Site U1437 in the Izu Bonin rear arc to investigate magnetic mineral diagenesis in deeply buried sediments from ~775 to ~1,002 m below sea floor (mbsf) with burial temperatures ranging from ~67 to 85 °C. Nonsteady state geochemical environments occur within an unusual deep methanic zone (below 850 mbsf) because of a release of sulfate below the shallow sulfate reduction zone. A drastic decline in magnetic susceptibility and remanence is observed at ~850 mbsf due to a decrease in ferrimagnetic iron oxide contents. Reduction of (titano)‐magnetite and pyritization occur at this inferred deep sulfate‐methane transition zone. Below ~850 mbsf, lower magnetic mineral contents coincide with further methane release. Geochemical analyses support a change in redox conditions and secondary precipitation of iron sulfides and carbonates in the methane‐rich zone. Magnetic mineral alteration is enhanced in zones where methane accumulates underneath low porosity intervals that act as seals. Although geochemical processes due to methane occurrence are likely dominant, more than one mechanism, possibly involving microbial activity, is probably responsible for the observed magnetic mineral assemblage changes.

Variações de intensidade do campo geomagnético em Santa Maria (Brasil) para os últimos 3 mil anos

Earth magnetic field variations at secular scales and at hundred quilometers have internal origin at the outer core. The most important feature associated with this internal field is the South Atlantic Magnetic Anomaly (SAMA), which covers the South America and it is characterized by the lowest total field intensity at the surface. Here, we investigate the geomagnetic field variations in Santa Maria (Brazil) over the past 3 ka. Results indicate that the intensities observed in Santa Maria are the lowest of the geomagnetic field over the past 3 ka. The consequences of these field features could be the increase in the electrically charged particles reaching the low Earth atmosphere that may generate problems in the communications systems or climate changes.

Мониторинг вариации геомагнитного поля на высокогорной биосферной станции «Джуга» и прогнозирование экстремальных природных событий

In the paper realization of the research project connected with monitoring of the Earth magnetic field variations at the high-mountain biosphere station «Dzuga» is considered. The acoustic channel of influence of the space weather and technologies of visualization of the geomagnetic and acoustic fields with use of high-sensitivity model experimental systems is considered. The new concept of forecasting of extreme natural events with use of the universal phenomenon of spacial self-synchronization of oscillations of geomagnetic and acoustic fields and on the basis of the analysis of the structure of holograms of physical fields is formulated.

Параметры линии электропередачи как фактор проявления геомагнитно-индуцированных токов

The results of comparison the level of higher harmonics industrial current and variation of Earth magnetic field are led on the example of local power grid of Kamchatka. It is shown a degree of correlation designated processes defined topological and construction parameters of electric systems. Modeling geomagnetically induced currents have been done for the part of Kamchatka’s power grid. Line from Petropavlovsk-Kamchatskiy to the settlement Ribachiy with length equal to 105 km, have been taken as the object of modeling. Since power line is characterized of distribution parameters such as capacity, inductivity and resistance, assessment of its resonance properties has been done. The comparison of modeling results and experimental data of variation of high harmonics of industrial current has been done. Comparison of our results and data of geomagnetically induced currents measurement of the USA power grid in similar geomagnetic conditions has been done.

Diurnal and Seasonal Variations in Mid-Latitude Geomagnetic Field During International Quiet Days: BOH Magnetometer

Korea Astronomy and Space Science Institute researchers have installed and operated magnetometers at Bohyunsan Observatory to measure the Earth's magnetic field variations in South Korea. In 2007, we installed a fluxgate magnetometer (RFP-523C) to measure H, D, and Z components of the geomagnetic field. In addition, in 2009, we installed a Overhauser proton sensor to measure the absolute total magnetic field F and a three-axis magneto-impedance sensor for spectrum analysis. Currently three types of magnetometer data have been accumulated. In this paper, we use the H, D, Z components of fluxgate magnetometer data to investigate the characteristics of mid-latitude geomagnetic field variation. To remove the temporary changes in Earth's geomagnetic filed by space weather, we use the international quiet days' data only. In other words, we performed a superposed epoch analysis using five days per each month during 2008-2011. We find that daily variations of H, D, and Z shows similar tendency compared to previous results using all days. That is, H, D, Z all three components' quiet intervals terminate near the sunrise and shows maximum 2-3 hours after the culmination and the quiet interval start from near the sunset. Seasonal variations show similar dependences to the Sun. As it becomes hot season, the geomagnetic field variation's amplitude becomes large and the quiet interval becomes shortened. It is well-known that these variations are effects of Sq current system in the Earth's atmosphere. We confirm that the typical mid-latitude geomagnetic field variations due to the Sq current system by excluding all possible association with the space weather.

Latitudinal signature of Earth's magnetic field variation over the last 5 million years

In order to investigate the latitudinal effect of the geomagnetic field variation, a new data set consisting of virtual geomagnetic poles (VGPs) from all latitudes has been produced. Since the updated data set was limited to data with VGPs within 45° of the geographic poles, data from lava flows with low‐latitude VGPs were added. More rigorous criteria were used to winnow the data. The data were divided into groups from different observation latitudes. In each group it was shown that the distribution of VGP latitudes could be described by a predominance of poles (average 82%) following a Fisher distribution with the rest following a distribution that would produce a uniform number of poles as a function of latitude. A distribution composed of two Fisher distributions also fit the data very well. For the case using a Fisher distribution plus a uniform distribution, the Fisher distribution changed such that the angular standard deviation (ASD) of VGPs from a set of observations taken at the equator is about 10° and the ASD at 60° observation latitude is about 19°. These results are similar to some results seeking to determine the ASD of VGPs as a function of observation latitude using other methods, which have been recently published, but there are also discrepancies. The results allow us to model inclination distributions as a function of observation latitude for comparison with data in which only the inclination is known, such as data from drill holes. It is shown that in order not to have doubt about the polarity of the inclination data, a drill hole has to be located at an absolute latitude greater than 27° for there to be less than a 5% error. This has major importance for the location of the “Mission to the MOHO” of the Integrated Ocean Drilling Program. The results also confirm that the sources of the nondipole field located in the outer core have to be more than twice as strong at high latitudes than at low latitudes so as to produce the observed increase in VGP scatter with observation latitude. The model of the secular variation proposed here is in no way a theory about how the secular variation happens, but it does allow those who wish to develop such a theory to have a model distribution with which to check their predictions.

Signal conditioning for GMR magnetic sensors: Applied to traffic speed monitoring GMR sensors

The Earth's magnetic field provides a uniform magnetic field over a wide area of several kilometers, among 30 and 60 μT depending on the location. Thus, cars, which have a high ferrous content mainly under car parts, provoke local disturbances around 1 μT over the constant Earth's magnetic field whether it is moving or still standing. Giant Magneto-Resistance (GMR) gradient sensors are able to convert this Earth's magnetic field variations into a voltage signature, due to the “Giant Magnetoresistive Effect”. Nevertheless, the output of the GMR sensors is too weak to operate with, and it must be amplified and filtered enough to be digitized and then processed. In this paper, we show the design and implementation of a practical conditioner circuit for GMR sensors and a simple speed calculation algorithm used in our embedded speed monitoring system for vehicles. The signal conditioner has been adjusted for car applications, where a high gain in a certain bandwidth is required due to the relatively large distance between the sensors on the pavement and the under car parts. Our conditioning circuit amplifies the sensor's output voltage by 36.360 in a bandwidth among 0.19 and 48.23 Hz. We present, compare and analyze two real car signals captured with our embedded system. With the small and cheap magnetic sensors and only a few additional components, our embedded speed monitoring system is suitable in automotive applications, where it would drastically reduce the cost of the expensive installation procedures of current car speed monitoring systems or even car detecting systems.

Earth magnetic field and geomagnetic activity effects on long-term trends in the F2 layer at mid-high latitudes

It is well known that the Earth magnetic field, as well as geomagnetic activity, presents long-term variations. Both phenomena affect the height of the F2 layer peak, hmF2, and the maximum electron concentration estimated by foF2. Experimental data of three mid-high latitude stations (Argentine Islands, Slough and Uppsala) were used to estimate foF2 long-term trends. These trends were compared with a theoretical approximation considering long-term variations in the Earth magnetic field, and also with a qualitative assessment of geomagnetic activity increasing trend effects. Although the agreement between experimental and theoretically approximated trends is not within a desired acceptance level, the ability of the Earth's magnetic field variations to produce trends in the F2 layer of the ionosphere may be an important result. Long-term trends in geomagnetic activity could possibly explain some discrepancies such as the seasonal pattern of Slough and Uppsala, with lesser negative trends in winter, and also the similarity in the trend pattern of both northern stations.

Quality of pTRM acquisition in pyrrhotite bearing contact-metamorphic limestones: possibility of a continuous record of Earth magnetic field variations

The rockmagnetic and palaeomagnetic signal in pyrrhotite bearing limestones of different contact-metamorphic settings were investigated related to intrusions ranging from small sills to large magmatic complexes. Magnetic susceptibility, the pyrrhotite/magnetite ratio and thermal modelling serve as an investigative tool to define three metamorphic zonations: a contact zone of a mixed magnetic assemblage and low susceptibilities, a pyrrhotite bearing transitional zone, where full thermoremanent magnetisations (TRMs) are acquired due to temperatures above the Curie temperature of pyrrhotite ( T c,po), and a marginal zone containing pyrrhotite and magnetite generated at temperatures below T c,po. The fact that TRMs can consist of independent pTRMs is successfully tested by modified Thellier experiments. It is shown that a metamorphic environment with low fluid circulation provides a scenario for the recording of independent pTRMs. Multicomponent behaviour of the NRM residing in samples from the transitional zone can therefore be interpreted as a continuous record of Earth magnetic field variations.

Palaeosecular variation recorded by lava flows over the past five million years

We present a new global palaeomagnetic database, comprising lava flows and thin intrusive bodies, suitable for studying palaeosecular variation and the time-averaged field. The database is presented in some detail in the appendix and is available on-line from the authors. We review palaeosecular variation models to date, emphasizing the assumptions required and the rather arbitrary construction of many of these models. Preliminary studies of the statistical properties of the new database suggest that existing palaeosecular variation models are inadequate to explain the long-term temporal variations in the field. It is increasingly apparent that data distribution and quality are pivotal in determining the characteristics of the secular variation. The work presented here demonstrates the need for revised models of the time-averaged field structure for both normal and reverse polarities before reliable models for palaeosecular variation can be made.

MAGNETIC DISTURBANCES, SPORADIC E, AND RADIO ECHOES ASSOCIATED WITH THE AURORA

A comparison of simultaneous data on the visible aurora, the earth's magnetic field variation, vertical and oblique ionosonde echoes, and very-high-frequency radar echoes has been made. Long-range high-frequency and very-high-frequency radio echoes do not appear to correlate individually. Reflections are observed, however, on both frequency ranges coincident with the appearance of low elevation auroral arcs, which are associated with magnetic bays.

Notes And personalia

The Geophysical Institute at the University of Alaska had its origin in 1929 when a grant from the Rockefeller Foundation established the means for studies of auroral heights. During the International Polar Year of 1932–1933, the University of Alaska was designated a first order station in the network engaged in seismological, terrestrial magnetic, electric potential measurements, auroral investigations, and study of the ionosphere. From 1934 to 1941 a portion of the Polar Year program was continued.In 1941 a cooperative research endeavor was inaugurated by the Department of Terrestrial Magnetism, Carnegie Institution of Washington, and the University of Alaska directed towards an exact and systematic study of the ionosphere, oblique incidence radio wave propagation, and the Earth's magnetic field variations. The seismological work was continued for United States Coast and Geodetic Survey.