Total Geomagnetic Field Research Articles

On the Application Limits of the Parameter in Studying Variations of the Ancient Geomagnetic Field

To describe secular geomagnetic variation on geological timescales, statistical models have been widely used in recent decades. Currently, the most popular among these is the TK03 model (Tauxe and Kent, 2004). As other statistical models, TK03 numerically characterizes the amplitude of secular geomagnetic variation and the shape of the distribution of paleomagnetic directions which are considered as directly reflecting the directions of the geomagnetic field on the considered interval of geological time. For this purpose, three main parameters are used: the scatter Sb (or S) of the virtual geomagnetic poles, the elongation E of the distribution of paleomagnetic directions, and the direction of elongation of the distribution of paleomagnetic directions. The correct application of these parameters to describe ancient secular variation requires the satisfaction of certain, sometimes rather strict conditions. These conditions for the Sb and E parameters were considered in a number of previous publications, while the limits and conditions of application of parameter have not been studied in detail so far. This paper presents the results of mathematical modeling that allow us to evaluate the stability of the calculated values of this parameter as a function of the latitude of sampling, the number of samples used for its determination, the length of the time series on which this parameter is determined, as well as inclination shallowing and the degree of averaging when is estimated in sedimentary rocks. We also consider the extent to which the parameter can be sensitive to the presence and characteristics of the equatorial dipole component in the total geomagnetic field.

Compensation Method for the Carrier Magnetic Interference of Underwater Magnetic Vector Measurement System

This paper proposed a new compensation method of underwater magnetic vector measurement system which innovatively using the geomagnetic total field as benchmark. Moreover, this method does not require the use of heading angle data in the calculation of the compensation parameters, which avoids errors caused by insufficient accuracy of underwater heading angle. The implementation of these features relies on the new objective function constructed according to the characteristics of the spatial projection of the magnetic vector field on the horizontal plane of the geographical coordinate. The core matrix of the geomagnetic vector ellipsoid model is used as a constraint to determine the range of function solutions. The Levenberg-Marquardt algorithm is used to find the optimal solution to the new objective function. Three experiments were carried out to verify the proposed method. In simulation experiment, the deviation between the calculated value and the preset value is less than 0.01%. In field experiment, the standard deviation value of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x, y, z</i> magnetic components and the root mean square error of magnetic total field after compensation are reduced from 1527.38nT, 1397.35nT, 1529.16nT, 574.94nT to 9.86nT (0.65%), 9.99nT (0.72%), 5.63nT (0.38%), 2.14nT (0.37%). The proposed method is finally verified by marine experiment. The standard deviation value of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x, y, z</i> magnetic components and the root mean square error of magnetic total field after compensation are reduced from 575.02 nT, 830.60 nT, 620.95 nT, 1702.35 nT to 17.43 nT (1.11%), 14.14 nT (1.70%), 25.17nT (4.10%), 7.18 nT (0.42%).

The decrease in diurnal oxygen production in Elodea under the influence of high geomagnetic variability: the role of light, temperature and atmospheric pressure

Epidemiological studies have indicated adverse effects of geomagnetic disturbance on human health, including increased mortality. There is evidence from plant and animal studies that help to elucidate this interaction. This study tests the hypothesis that geomagnetic disturbance affects living systems, by modifying the metabolic process of photosynthesis, in the natural environment.Continuous 24-h measurements of dissolved oxygen in flasks containing Holtfreiter’s solution and strands of healthy Elodea were recorded from May 1996, until September 1998, in an electromagnetically quiet, purpose built, garden shed environment, without mains electricity. Sensormeter recordings of oxygen, light, temperature and air pressure were uploaded weekly to a PC. The hourly total geomagnetic field measurements were obtained from the nearest observatory.Significant decrease in oxygen (diurnal volume of oxygen divided by plant mass and diurnal light), (O/WL), was found on days of high geomagnetic field variability throughout 11 recorded months of the year 1997. This result was independent of temperature and atmospheric pressure. No significant decrease in O/WL during high geomagnetic variability was found for the 7 months recorded in 1996. The 1996 and 1997 data both showed a significant decrease in the diurnal time lag between peak light and peak oxygen for diurnal high geomagnetic variability compared with low geomagnetic variability. Cross correlation analysis for 1997 and 1998 data showed a decrease in positive correlation of oxygen with light in high geomagnetic variability, compared with low geomagnetic variability, and increased positive correlation with the geomagnetic field instead. These experiments support a hypothesis of high geomagnetic field variability as a weak zeitgeber, and a metabolic depressant for photosynthetic oxygen production in plants.

Simple Graphical Pre- and Post-Processor for 3-D Magnetotelluric Inversion

To understand a field of volcanic activity, a survey on the Earth’s subsurface structure is helpful. In particular, a magnetotelluric survey can image the subsurface structure necessary for volcanic disaster prevention because it is sensitive to high-temperature areas and areas where fluid and clay minerals exist. In 3-D magnetotelluric inversion using the data observed near volcanoes and the coastline, the topography and sea around the survey area need to be considered. Therefore, constructing a mesh of the analysis area by automatically using topography and bathymetry data is necessary. Additionally, the estimated subsurface structure should be compared to the sources of variation estimated from other physical observations, such as earthquakes, ground deformation, and changes in the geomagnetic total field, for interpretation. This study introduces a simple and easy-to-operate graphical pre- and post-processor developed to support the resistivity structure analysis of a volcano and the nearby coastline. In the developed software, the pre-process indicates the mesh construction, and the post-process indicates result derivation, file construction for the sensitivity tests, and file exportation to compare the inversion results with other measured quantities. This pre- and post-process can be performed easily on the same window of the software.

The Multifractal Detrended Fluctuation Analysis (Mf-Dfa) and Anomalies in Geomagnetic Total Field Intensity Prior To Mw~5.5 Earthquake

In the research article, we report the anomalies observed in geomagnetic total field intensity (BTotal) prior to Mw 5.5 Kokrajhar event. The multifractal analysis was scrutinized to reveal the underlying dynamics in the Geomagnetic Total field intensity time series. The multifractal spectrum on the day when the event occurred (TEvent day) and its surrogate (TSurrogate) was investigated to understand the behavior and dynamics hidden in BTotal time series. A significant variation in the multifractal spectrum was observed between TDay one (multifractal spectrum a day prior to the event) and TEvent day. It was also observed that the mulfractality of BTotal when the event occurred (TEvent day) got stronger than the multifractality of TDay one and was sourced from low values distribution. The multifractality in TDay one and TEvent day time series was not from source type long range correlation or sourced from broad probability density function. The investigation also manifests some non-linear features which probably evinces the anomalies to be seismic induced. The observations are elaborately emphasized in the article. The study scrutinizes the underlying dynamics in geomagnetic field intensity time series for earthquake precursory and forecast studies.

Extended isolation forest – application to outlier detection in geomagnetic data

The aim of this study is to present a method for detection of outliers in the time series of total intensity of geomagnetic field using Extended Isolation Forest algorithm. The method is consisted of three steps: 1) generation of additional features that take into account the regular daily variation and smooth behaviour of normal data, 2) detection of potential outliers based on ensemble of extended isolating trees and 3) subsequent refinement based on difference between the outlier and its replacement with interpolated value. Application of the method for detection of outliers in yearly time series of the total geomagnetic field at Ak-Suu and Kegety stations showed that the algorithm identifies both global and contextual outliers. Average classification metrics for the method are characterized as high and have the following values: precision 94.3%, recall 93.9% and F-score 94.5%, and probabilities of errors of the first and second kind are comparable to similar algorithms used for detection of outliers in magnetograms of different sampling rate.

Possible External Factors Determining Ultradian (4-20-min) Rhythms of Body Temperature.

The study examined the effect of passive magnetic shielding on the magnitude of rhythmic oscillations of body temperature (BT) with 4-20 min periods in mice and their correlation with similar oscillations in unshielded control group. A magnetic permalloy screen that 35-fold attenuates the total geomagnetic field and decreased the undulations of magnetic field with the periods of few minutes by 5 times, produced no effect on the mean amplitude of BT oscillations within the same period range, their spectral power, and the cross-spectral density of examined rhythms in comparison with the control (unshielded) mice. Thus, either the mice possess a very sensitive magnetic sensory system or there exists an external non-magnetic factor affecting rhythmicity of BT. The study advanced intensity of thermal neutron radiation near the Earth's surface known to reflect the flow of accelerated particles generated by the secondary cosmic rays as the external factor, which strongly correlates with BT rhythms revealed by cross-spectrum analysis.

Thermoelectric model of the Earth's magnetic field

A variant of the thermoelectric model of the Earth's dipole magnetic field is considered. It is based on geothermoelectric currents present in the planet's core. The currents cyclically change their direction, which leads over time either to warming on the Earth, if their movement is directed towards the Earth's crust, or to cooling, when moving towards the inner core. With each change in the direction of movement of the thermal currents, the poles of the Earth's magnetic field are inverted simultaneously. The inversion process is instantaneous (on the scale of planetary time) and is not the result of a gradual reversal on the 180° Earth's magnetic axis. At the moment of inversions of thermal currents in the core, the total geomagnetic field decreases to the level of 4.6∙10-6 T, which is constantly supported by thermal currents of semi-conducting rocks of the lower mantle. The considered version of the thermoelectric model of the Earth's magnetic field may be promising for studying the magnetic fields of planets in the Solar system.

Characteristic periods of the paleosecular variation of the Earth's magnetic field during the Holocene from global paleoreconstructions

The knowledge of the secular variation of the geomagnetic field at different time scales is important to determine the mechanisms that maintain the geomagnetic field and can help to establish constraints in dynamo theories. We have focused our study on the secular variation at millennial and centennial time scale searching for characteristic periods during the last 10 kyr. The frequency study was performed using four recent updated global paleomagnetic field reconstructions (SHA.DIF.14k, CALS10k.2, BIGMUDI4k and SHAWQ2k) by applying three techniques commonly used in signal analysis: the Fourier transform, the Empirical Mode Decomposition, and the wavelet analysis.Short-term variability of the geomagnetic field energy shows recurrent periods of around 2000, 1000–1400, and 600–800 and 250–400 years. The characteristic time around 600–800 years is well determined in all paleomagnetic reconstructions and it is mostly related to the axial dipole and axial octupole terms, but also observable in the equatorial dipole. In addition to this period, longer characteristic times of around 1000–1400 years are found particularly in the equatorial dipole and quadrupole terms in SHA.DIF.14k, CALS10k.2 and BIGMUDI4k while the 2000 year period is only well determined in the total geomagnetic field energy of SHA.DIF.14k and CALS10k.2. The most detailed paleoreconstructions for younger times also detect shortest characteristic times of around 250–400 years.The long-term variation of the geomagnetic energy is only observable in the axial dipole. A characteristic period of around 7000 years in both SHA.DIF.14k and CALS10k.2 has been found. This long period is related to two decays in the dipole field and a period of increasing intensity. The oldest decay took place between 7000 BCE and 4500 BCE and the present decay that started around 100 BCE. We have modeled the 4500 BCE up to present variation as a combination of a continuous decay, representing the diffusion term of the geomagnetic field, and one pulse that reinforces the strength of the field. Results show a characteristic diffusion time of around 11,000–15,000 years, which is compatible with the diffusion times of the dipole field used in geodynamo theories.

Measurement of Far Field Magnetic Moment Vector of a Moving Ferromagnetic Object

In magnetic anomaly detection, it is a prerequisite to master the far-field magnetic moment vector information of the target. It is important to measure the magnetic moment of the target in target location, recognition and degaussing. In the paper, we proposed a method of measuring the magnetic moment vector of the target based on the total geomagnetic field. In this method, a sensor array with the scalar magnetometers was constructed and the quantitative factors of the magnetometer were analyzed. In order to eliminate the time-varying and uneven spatial distribution of geomagnetic total field, a double gradient algorithm was applied to magnetic moment measurement in this method. And a criterion function of determining the magnitude and direction of the target magnetic moment was defined. The proposed method was validated by the theoretical calculation and real experimental data. The results showed that the measured magnetic field data were qualitatively in good agreement with the theoretical curve. For the magnitude of magnetic moment, the average relative deviation was 5.1%. And the average relative deviation of inclination and declination of the moment were 3.2% and 2.5%, respectively. In addition, we attempted to separate the induced magnetic moment and the intrinsic magnetic moment of the target. The proposed method can be used as a reference for the target magnetic location and demagnetization.

Analysis of Magnetic Anomaly Characteristics of Underground Non-Coplanar Cross-buried Iron Pipelines

The non-coplanar cross-buried pipelines are a common way of pipeline wiring. In order to investigate the magnetic anomaly characteristics of the non-coplanar cross-buried pipelines and guide the site operation, the influences of a series of factors on the magnetic anomaly of the non-coplanar cross-buried pipelines are analyzed. Based on the principle of magnetic dipole construction, a forward model is established for the magnetic anomaly characteristics of the subsurface non-coplanar cross-buried pipelines. The basic characteristics of magnetic anomaly for the non-coplanar cross-buried pipelines are defined. The influences of geomagnetic parameters (geomagnetic intensity, geomagnetic inclination, and geomagnetic declination), pipeline parameters (thickness, magnetic susceptibility), and cross angle of pipelines on the characteristics of magnetic anomalies are analyzed. The results show that the shape of the total magnetic anomaly is mainly affected by the magnetic inclination, and the curve of magnetic anomaly at ± I site shows some symmetry. The amplitude is approximately linearly affected by the total geomagnetic field, magnetic declination, pipeline thickness, material magnetic susceptibility, and pipeline cross angle. There is a periodic change of the amplitude with the increase of geomagnetic inclination (−90°–&gt;90°). The crest-trough distance is mainly affected by geomagnetic inclination, magnetic declination, thickness, magnetic susceptibility, and pipeline cross angle. A more accurate measurement can be achieved if the direction of the pipelines is roughly measured and then the number of measurement points is augmented near the intersection of pipelines and the measurement lines. Present work obtains the equivalent magnetic dipole units by segmenting pipelines. The magnetic anomaly characteristics of non-coplanar crossed iron pipelines are successfully simulated. The numerical results are in accordance with the experimental analysis.

Experimental Study on the Aperture of Geomagnetic Location Arrays

A method of locating a magnetic target based on geomagnetic total field is proposed. In the method, a conjugate gradient algorithm is introduced to eliminate the time-varying and uneven spatial distribution of geomagnetic total field. Then a structure of the measuring array of geomagnetic total field is designed. In the measuring array, the array aperture is a primary factor for the conjugate gradient algorithm. To determine an optimal aperture, we analyze the relationship between the array aperture and the localization accuracy. According to the localization theory based on geomagnetic total field, we simulate the process of determining an optimum array aperture. Based on the simulation, we propose the basis and principle of determining the optimum array aperture. To prove it, we use optically pumped magnetometers with different array apertures to carry out the experiments of locating a car in a suburb. Through the experiment, we get the experimental relationship between apertures and location accuracy. And the relationship agrees with the theory. The result shows that the method is feasible to determine the optimum aperture.

Geomagnetic Mapping of the Macaé Region, Brazil

This work presents the geomagnetic characterization of the municipality of Macae, Brazil. Data from IGRF12 (twelfth edition of International Geomag-netic Reference Field) were used. Through the data collected in a regular grid of 0.1 degrees of the components, north, east and vertical were generated maps of components, inclination, declination, horizontal component and geomagnetic total field. The results showed important relative variations of these magnitudes, such as the magnetic declination that varied around 0.2 degrees along the area of the municipality, which is a considerable value and capable of causing significant changes in directions by compass in the studied region.

Solar coronal holes and their geo-effectiveness

Solar corona as the outermost part of the Sun is constantly emanating solar wind consisting of charged particles. Coronal holes are rigidly rotating phenomena in the solar corona that are magnetically open to interplanetary space, which allow the solar wind particles to escape from the Sun. The study of coronal holes and their associated high speed solar wind streams is important because they are the sources of space weather disturbances during minimum solar activity. We present some results on the relationship between large solar coronal holes close to the central meridian and solar wind stream with the aim to analyse their geo-effectiveness. The analysis were carried out by considering geomagnetic and solar wind parameters such as total geomagnetic field, Bz component, proton density and plasma speed during Earth-side large solar coronal holes appearance. Using the data during declining phase solar activity we found that a solar coronal hole is geo-effective during and after its transit on the central meridian but not all of them can be the proxy of high speed solar wind.

Correlation between lithospheric magnetic anomalies and tectonic structures in the Norwegian-Greenland region of the Arctic

The studies of the deep structure and tectonics of the Arctic are important for solving the fundamental problems of modern geodynamics and developing its natural resources. This region is also of interest from the geopolitical point of view, in particular, considering the boundaries of the marginal seas. Our study aims to investigate the lithospheric (anomalous) geomagnetic field in the Norwegian-Greenland region of the Arctic and to correlate the identified anomalies with tectonic structures located in the region under study. The database includes the CHAMP satellite measurements of the modulus of the total geomagnetic field vector (the satellite operated at the altitude of ~280 km). This article describes the satellite data processing method applied to distinguish between the lithospheric part and other components of the geomagnetic field. Map showing the total vector modulus of the lithospheric field has been constructed for the studied area. The article discusses the possible nature of the lithospheric magnetic anomalies and their relation to the processes that occur under the territory of Greenland. According to our interpretation of the maps, the geomagnetic field anomalies are related to the modern large-scale geological and tectonic structures located in the studied area. The obtained results can facilitate further comprehensive geological and geophysical studies and contribute to modeling of the evolution of the lithosphere.

Analysis of the ultra-low frequency magnetic field fluctuations prior to the 2016 Kumamoto (Japan) earthquakes in terms of the method of critical fluctuations

The method of critical fluctuations (MCF) is a time series analysis method which provides a way of both identifying the critical state and the departure from it. Its application to the ground-based ultra-low frequency (ULF) magnetic field fluctuations observed prior to the very strong earthquakes (EQs) of magnitudes MW=6.2, MW=6.0 and MW=7.0 which sequentially took place within a two days period (April 14–15, 2016) in Southwest Japan under the city of Kumamoto reveals when the underlying process reached critical state, as well as when it departed from critical state. Specifically, critical dynamics was identified in the raw total geomagnetic field intensity (F) ULF recordings of the Kanoya (Japan) station ∼4 d before the MW=6.2 and ∼5 d before the MW=7.0 event. Moreover, the progressive development of the symmetry breaking phenomenon, which signifies departure from critical state, was identified in later recordings. Specifically the phenomenon evolved from a few hours before the MW=6.0 event until a few hours after the occurrence of the specific EQ, which was a few hours before the MW=7.0 event. The detected combination of phenomena, i.e., the detection of critical state followed by the detection of the departure from the critical state by means of symmetry breaking, indicates that the main event was the third and strongest EQ, while the two preceding EQs were strong foreshocks.

Effects of solar activity and galactic cosmic ray cycles on the modulation of the annual average temperature at two sites in southern Brazil

Abstract. Quasi-periodic variations in solar activity and galactic cosmic rays (GCRs) on decadal and bidecadal timescales have been suggested as a climate forcing mechanism for many regions on Earth. One of these regions is southern Brazil, where the lowest values during the last century were observed for the total geomagnetic field intensity at the Earth's surface. These low values are due to the passage of the center of the South Atlantic Magnetic Anomaly (SAMA), which crosses the Brazilian territory from east to west following a latitude of ∼ 26∘. In areas with low geomagnetic intensity, such as the SAMA, the incidence of GCRs is increased. Consequently, possible climatic effects related to the GCRs tend to be maximized in this region. In this work, we investigate the relationship between the ∼ 11-year and ∼ 22-year cycles that are related to solar activity and GCRs and the annual average temperature recorded between 1936 and 2014 at two weather stations, both located near a latitude of 26∘ S but at different longitudes. The first of these stations (Torres – TOR) is located in the coastal region, and the other (Iraí – IRA) is located in the interior, around 450 km from the Atlantic Ocean. Sunspot data and the solar modulation potential for cosmic rays were used as proxies for the solar activity and the GCRs, respectively. Our investigation of the influence of decadal and bidecadal cycles in temperature data was carried out using the wavelet transform coherence (WTC) spectrum. The results indicate that periodicities of 11 years may have continuously modulated the climate at TOR via a nonlinear mechanism, while at IRA, the effects of this 11-year modulation period were intermittent. Four temperature maxima, separated by around 20 years, were detected in the same years at both weather stations. These temperature maxima are almost coincident with the maxima of the odd solar cycles. Furthermore, these maxima occur after transitions from even to odd solar cycles, that is, after some years of intense GCR flux. The obtained results offer indirect mathematical evidence that solar activity and GCR variations contributed to climatic changes in southern Brazil during the last century. A comparison of the results obtained for the two weather stations indicates that the SAMA also contributes indirectly to these temperature variations. The contribution of other mechanisms also related to solar activity cannot be excluded. Keywords. Meteorology and atmospheric dynamics (climatology)

Indonesian Geomagnetic Maps for Epoch 2015.0 to cover of Indonesian Regions

In compliance with the resolutions of IAGA (International Association of Geomagnetism and Aeronomy), Since 1960’s, every five years BMKG or Meteorology, Climatology and Geophysics Agency of Indonesia made geomagnetic field maps based on actual measurements in 53 repeat stations. It’s the map for more accurate result of Geomagnetic maps Epoch 2015.0, the number of repeat stations has been increased to 68 locations. Analysis data was conducted by spatial analyses using collocated co-kriging and kriging with external drift to map the observation data in five components, such as Declination (D), Inclination (I), Vertical (Z), Horizontal (H), and Total Geomagnetic Field (F). The data reduction used one permanent observatory i.e., Kupang Geophysical Observatory, as a reference standard. The results of this Geomagnetic Maps, that the contour lines of Indonesian geomagnetic declination in range -1 to 4.5 degree, Inclination component are -5 to -37 degree, Vertical component are -4000 to -28000 nT, Horizontal component are 36000 to 42000 nT, and Total Geomagnetic Field are 39000 to 46000 nT. In conclusion, Indonesian Geomagnetic Maps for Epoch 2015.0 can be used to compute geomagnetic data around Indonesian regions until next 5 years.

Experimental Study on the Localization of Moving Object by Total Geomagnetic Field

In the method of target localization based on magnetic anomalies, the scheme of vector field localization and experimental research are significant. Because more information of magnetic field can be measured by vector sensors, the position of the target can be directly calculated by the equations. However, the vector magnetic anomaly generated by the target is difficult to measure. And the detection range is small due to the low sensitivity of vector sensors. A method for target localization based on the total geomagnetic field is proposed. Its advantages are that the measurement of total magnetic field is not affected by the orientation of the total field sensors and the detection range is large due to their high sensitivity. In this paper, we focus on the localization using the array with the total field magnetometers. And we design an array structure with the total field magnetometers. Then, we obtain the higher order nonlinear equations for the target localization based on this array. The numerical method is used to solve the equations. Meanwhile, we present a method for eliminating the effect of geomagnetic field variations and uneven spatial distribution. In suburban roads, localization experiments were carried out. And the results showed that the relative error of target localization is less than 5% by using the proposed method.

Real-Time Tracking Method for a Magnetic Target Using Total Geomagnetic Field Intensity

We propose an efficient and effective method for real-time tracking a long-range magnetic target using total geomagnetic field intensity. This method is based on a scalar magnetometer sensor array and an improved particle swarm optimization algorithm. Due to the effect of the geomagnetic field variations, the detection distance range of the method based on the gradient tensor is short. To increase the detection range, the geomagnetic field variations must be eliminated in the method. In this paper, the geomagnetic quasi-gradient calculated from total geomagnetic field intensity in the sensor array is used. We design a sensor array with five magnetometers and use the geomagnetic quasi-gradient to eliminate the geomagnetic field variations. The improved particle swarm optimization (IPSO) algorithm, which minimizes the errors of total geomagnetic field values between measurements and calculations, is applied in this real-time tracking method to track a long-range magnetic target position. The detailed principle of the method and the steps of the IPSO algorithm are described in detail. The method is validated with a numerical simulation. The results show that the average relative error of position is less than 2 % and the execution time is less than 1.5 s.