Earth Currents Research Articles

Induction effects on ionospheric electric and magnetic fields

Abstract. Rapid changes in the ionospheric current system give rise to induction currents in the conducting ground that can significantly contribute to magnetic and especially electric fields at the Earth's surface. Previous studies have concentrated on the surface fields, as they are important in, for example, interpreting magnetometer measurements or in the studies of the Earth's conductivity structure. In this paper we investigate the effects of induction fields at the ionospheric altitudes for several realistic ionospheric current models (Westward Travelling Surge, Ω-band, Giant Pulsation). Our main conclusions are: 1) The secondary electric field caused by the Earth's induction is relatively small at the ionospheric altitude, at most 0.4 mV/m or a few percent of the total electric field; 2) The primary induced field due to ionospheric self-induction is locally important, ~ a few mV/m, in some "hot spots", where the ionospheric conductivity is high and the total electric field is low. However, our approximate calculation only gives an upper estimate for the primary induced electric field; 3) The secondary magnetic field caused by the Earth's induction may significantly affect the magnetic measurements of low orbiting satellites. The secondary contribution from the Earth's currents is largest in the vertical component of the magnetic field, where it may be around 50% of the field caused by ionospheric currents. Keywords. Geomagnetism and paleomagnetism (geomagnetic induction) – Ionosphere (electric fields and currents)

Air–earth current measurements at Kew, London, 1909–1979

A vertical conduction current arises from the global ionospheric potential and the integrated electrical resistance between the Earth's surface and the ionosphere. The conduction current density varies with the ionospheric potential and the vertical (columnar) resistance. At the surface, the conduction current density is known as the air–earth current. C.T.R. Wilson developed a measurement technique for the air–earth current in 1906, which was implemented by the British Meteorological Office at its Kew Observatory (51° 28′N, 0° 19′W) near London in 1909. Simultaneous measurements of air–earth current, potential gradient and positive air conductivity were made almost continuously until 1979 using the Wilson method on fine afternoons. A summary of the complete set of monthly mean measurements is presented here for the first time. The data span the nuclear weapons testing period and the UK Clean Air Act of 1956, both of which influenced the measurements obtained. Annual average values of the air earth current density at Kew are 0.97 pA·m −2 (1909–1931), 1.04 pA·m −2 (1932–1949) and 1.41 pA·m −2 (1967–1979).

Technical Note:Simulated Transient Loss of Cathodic Protection for Buried Pipelines

Abstract The effect of loss of cathodic protection (CP) on steel in soil is presented for simulated (anodic) telluric currents over and above CP currents. The potential of the steel is intentionally shifted to 0 V vs. silver/silver chloride (Ag/AgCl, saturated) for 20% of the test time in a cyclic manner (with a number of different cycle times tested). It is seen that the level of corrosion experienced by the steel is dominated by the length of individual transients and not cumulative anodic exposure. The nature of the soil was found to be important, with clay soil leading to significantly more corrosion than sandy soil.

The Potential Gradient of Ground Surface according to Shapes of Mesh Grid Grounding Electrode using Reduced Scale Model

In order to analyze the potential gradient of ground surface of grounding system installed in buildings, the hemispherical grounding simulation system has been designed and fabricated as substantial and economical measures. Ground potential rise (GPR) has been measured and analyzed for shapes of a mesh grid grounding electrode by using the system. The system is apparatus to have a free reduced scale for conductor size and laying depth of a full scale grounding system. When a current flows through a grounding electrode, the system is constructed so that a shape of equipotential surface is nearly identified a free reduced scale model with a real scale model.The system was composed of a hemispherical water tank, AC power supply, a movable potentiometer, and test grounding electrodes. The water tank was made of stainless steel and its diameter was 2m. AC power supply produced earth leakage current. GPR was measured by a moving probe of a potentiometer horizontally. The test grounding electrodes were fabricated through reducing grounding electrode installed in real buildings such as a mesh grid type, a combined type and so on. GPR has been measured in real time when a test current has flowed through grounding electrode. GPR was displayed in two-dimensional profile and was analyzed for shapes of a grounding electrode. When a mesh grid type was associated with a rod type and auxiliary mesh electrodes were installed at the four sides of mesh grid grounding electrode, GPR was the lowest of all test grounding electrodes. The proposed results would be applicable to evaluate GPR in the grounding systems, and the analytical data can be used to stabilize the electrical installations and prevent the electrical disasters.

Magnetic and Electric Fields of Direct Currents in a Layered Earth (Short Note)

We derive a numerical solution of the steady-state magnetic field due to a DC current source in a layered earth model. Such a solution is critical for interpretation of magnetometric resistivity (MMR) data. Our solution is achieved by solving a boundary value problem in the spatial wavenumber domain and then transforming back to the polar spatial domain. The propagator matrix technique is used to interrelate solutions between layers. Two simplified cases are examined to promote understanding of the magnetic fields. In particular, the derived formula illustrates why surface MMR data are insensitive to ID conductivity variations and why borehole measurements are effective in finding conductivity contrasts.

POWER LINE INDUCED CURRENT IN THE EARTH DETERMINED BY MAGNETOTELLURIC TECHNIQUES

Power frequency (60 Hz and harmonics) AC currents were measured on four Wisconsin dairy farms usingresistivity and potential gradient measurements by techniques adapted from magnetotelluric (MT) geophysical exploration.Several measurement sites were located on each farm in addition to a remote site as far away from the nearest power line ascould reasonably be achieved. Electric field intensity and earth resistivity measurements were used to calculate thenear-surface current density for 60 Hz and the 12 next order harmonics.<br><br>Earth currents and the corresponding electrical voltages at 60 Hz and higher harmonics were inconsistent from farm tofarm. Electric fields at the farms ranged from roughly 1 to 10 mV/m RMS at 60 Hz, and the current densities ranged from about5 to 50 .A/m2, roughly 10 to 1000 times stronger than at the corresponding remote sites. As expected, the presence of 60-Hzpower frequency current and its harmonics was stronger near points of electrical use and distribution.<br><br>The resulting step potentials, measured with high impedance equipment, were 26 to 8300 times lower than the maximumcow contact voltages prescribed by the Public Service Commission of Wisconsin (PSCW). Assuming a typical reduction ofhalf in the contact voltage with a 500-ohm body impedance the resulting current flow through a cow attributable to earthcurrents in this study was 50 to 16,000 times below the PSCW action level. Considering the substantial body of literaturesupporting the PSCW level of concern, the extremely low exposure levels resulting from earth currents would not be expectedto cause harm to dairy cows.

Reduction of Noise in Induced Polarization Data using Full Time-Series Data

There are a variety of noise sources that affect the accuracy of Induced Polarization (IP) data, e.g., cultural noise, varying self- potential, lightning strikes, telluric currents, and electromagnetic (EM) coupling. In this paper, we describe a new IP data collection system that collects full time-series data rather than just a single averaged windowed decay. The recording of the full time series allows for greater flexibility in analysing the data so that noise can be identified and removed.This paper outlines the process used to collect the time-series data, illustrates some of the many types of noise observed in the field, and demonstrates the superiority of the resulting IP data.

Spiral Patterns of the Rossby Wave

AbstractWe use quasi‐geostrophic motion equations describing large‐scale motion in the atmosphere to obtain the steady three‐dimensional stream field and the corresponding potential temperature, vorticity and divergence fields. Among them the three‐dimensional velocity field constructs a nonlinear autonomous dynamical system in the physical space. It is shown that the Rossby wave has a tilting spiral structure, which represents that the stream field is horizontal convergence at lower level and ascending motion in front of trough, but descending motion and horizontal divergence at lower level behind the trough. And these make westerlies momentum from the north and the south concentrate on the center regions of the Rossby wave. This is known ordinarily as the ‘negative viscosity’ phenomena. It implies that the rotation of the earth and mean current are playing an important role in forming the spiral structure of the Rossby wave.

Characterisation of cultural noise in the AMT band

As part of a project to investigate long-term exposure of low-level earth currents on dairy cows, an unusual multiple-site, remote-reference audio magnetotelluric (AMT) data set was acquired on four Wisconsin dairy farms and two remote sites in the summer of 2001. At each dairy, several five-component sites were recorded along with a remote located in a wildlife refuge, at a distance of roughly 30 miles from the farms. EMI MT24 systems were deployed under power line transformers, above and below three-phase transmission lines, in close proximity to machinery such as compressors, pumps, electric fences, and large fans. Data were recorded at the dairies with 20 m dipoles to capture the natural signal while not overloading the instrument electronics with high cultural signals. Sampling frequencies of 48, 9.6 and 2 kHz were employed. To accurately determine the characteristics of the earth?s fields, including the magnitude of the very narrow band-nature of 60 Hz signal and its harmonics, normal impedance estimation techniques using relatively short segments of the time series were found inadequate. Thus, the data were processed with a Fast Fourier Transform of length 524,288 applied to each of the 500,000 data point segments. Electrical resistivity data were acquired with Wenner array spacings of 1 to 10 m. Earth current densities were estimated from the 1 m resistivity values and the electric field data from the MT24. Short recording times were used to determine earth currents under different conditions, not to estimate the impedance. Hence, we present characteristics of various cultural noise sources to improve the knowledge base of what practitioners must deal with in noisy environments. We are not evaluating processing technique, but have applied some robust processing to observe if it is possible to attain impedance estimates in the presence of coherent noise and low signal strength.

Reduction of noise in Induced Polarization data using full time series data

There are a variety of noise sources which affect the accuracy of Induced Polarization data, such as cultural noise, varying self-potential, lightning strikes, telluric currents, EM coupling etc. In this paper we describe a new IP data collection system which collects full time series data rather than just a single averaged windowed decay. The recording of the full time series allows for greater flexibility in analysing the data to allow noise to be rejected or removed.This paper will outline the process used to collect the time series data, illustrate the many types of noise observed in the field and demonstrate the superiority of the resulting IP data.

Polarisation and precise calibration of the LEP beam energy

We report in this article on two issues of precision accelerator physics, performed at the LEP collider, that challenged international collaborations. The first result is an increase of the polarisation degree from an almost vanishing natural level to 50%, opening the way to energy calibration by resonant depolarisation. The second result is a systematic and precise determination of the collider centre-of-mass energy correcting for subtle effects such as the azimuthal variation of the beam energy, the magnets temperature, the effects of parasitic earth currents and terrestrial tides. It resulted in an extremely accurate test of the Standard Model and set significant constraints on the top quark and Higgs masses. To cite this article: J.-P. Koutchouk, M. Placidi, C. R. Physique 3 (2002) 1121–1130.

Modelling of geomagnetic induction in pipelines

Abstract. Geomagnetic field variations induce telluric currents in pipelines, which modify the electrochemical conditions at the pipe/soil interface, possibly contributing to corrosion of the pipeline steel. Modelling of geomagnetic induction in pipelines can be accomplished by combining several techniques. Starting with geomagnetic field data, the geoelectric fields in the absence of the pipeline were calculated using the surface impedance derived from a layered-Earth conductivity model. The influence of the pipeline on the electric fields was then examined using an infinitely long cylinder (ILC) model. Pipe-to-soil potentials produced by the electric field induced in the pipeline were calculated using a distributed source transmission line (DSTL) model. The geomagnetic induction process is frequency dependent; therefore, the calculations are best performed in the frequency domain, using a Fourier transform to go from the original time domain magnetic data, and an inverse Fourier transform at the end of the process, to obtain the pipe-to-soil potential variation in the time domain. Examples of the model calculations are presented and compared to observations made on a long pipeline in the auroral zone.Key words. Geomagnetism and paleomagnetism (geo-magnetic induction)

On the Generation of ULF Magnetic Variations by Conductivity Fluctuations in a Fault Zone

— Prior to the October 18, 1989 Loma Prieta M s 7.1 earthquake, Fraser-Smith et al. (1990) recorded a 10–100 fold increase in ultra-low frequency (ULF) magnetic fields near the earthquake epicenter. Several mechanisms for generation of these ULF fields by fluid flow in the earth have been advanced, but all appear to require unrealistic fluid velocities or hydraulic permeabilities to match the observations. As an alternative explanation, Merzer and Klemperer (1998) proposed that the increase in ULF magnetic fields could result from induced electric currents flowing in a fault-zone made temporarily much more electrically conductive by stress-induced reorganization of pore geometry. Using a numerical model we show that while this mechanism could produce a significant increase in ULF variations, mutual induction between the fault zone and the surrounding crust would probably limit the amplitude increase to levels well below those observed at Loma Prieta. We consider a variant on this quasi-static conductive fault zone model in which low frequency telluric currents are modulated by small higher frequency variations of bulk fault zone conductivity. We show that because the spectrum of natural EM variations is red, substantially larger relative increases in ULF magnetic fields could be produced by this mechanism with even small conductivity fluctuations at these frequencies. These variations would be easy to detect with a well-designed experiment, if they occurred. In principle this mechanism could explain the Loma Prieta ULF observations, however the magnitude of conductivity fluctuations that would be required to match the very large reported amplification factors still appears to be too large to be physically plausible.

Global synchrony in biospheric variations and influence on soil pH

Data collected from 1968 through 1997 showed a globally synchronous annual increase in soil acidity during the period June through August which was highly correlated with progressively decreasing geomagnetic field strength despite periodic local alterations in electromagnetic activity at the planetary boundary layer. Monthly determinations of soil pH for periods of one or more years at sites in Australia, South America, North America, Scotland, and Germany showed pH values to be consistently and significantly correlated with the monthly average geomagnetic field strength and the auroral electrojet values recorded during the time period covered by the data. Unweighed simple and multiple least squares linear regressions of soil pH on geomagnetic D, H, and Z, and the auroral electrojet gave r2 and p values as high as r2 = 0.9997, p = 0.0000. These relationships were subject to modifications in soil pH by telluric currents and electromagnetic events, such as thunderstorms and accompanying acid rain, occurring at the planetary boundary layer. Short-term variations in electrical conductivity of soil, in situ plant-available soil moisture, availability of soil mineral nutrient elements for plant uptake, soil pH, and the pH of fresh and stored samples of soil diluted 1:5 in water, rainwater, and other solutions, and Rn levels in soil and air were highly correlated with ambient telluric currents and with atmospheric electrical discharges. Decreasing soil pH values were consistently associated with decreased availability of soil mineral nutrients for plant uptake, lower foliar mineral element content in growing plants, and reduced health status, fertility, and productivity of herbivores. Rising pH values were accompanied by increases in available soil mineral nutrient elements and improvements in plant and animal health and productivity.

Study of electromagnetic emissions associated with seismic activity in Kamchatka region

Abstract. A review of data processing of electromagnetic emission observation collected at the Complex Geophysical Observatory Karimshino (Kamchatka peninsula) during the first 5 months (July–November, 2000) of its operation is given. The main goal of this study addresses the detection of the phenomena associated with Kamchatka seismic activity. The following observations have been conducted at CGO: variations of ULF/ELF magnetic field, geoelectric potentials (telluric currents), and VLF signals from navigation radio transmitters. The methods of data processing of these observations are discussed. The examples of the first experimental results are presented.

Detection of crustal inhomogeneity in the Nojima Fault zone using earth current noise

Abstract A resistivity survey method using artificial telluric noise was examined and applied to a field of a fault zone. The electric earth current was measured at 50 sites in the Nojima Fault zone, which is in the northwestern part of Awaji Island, southwestern Japan. The dominant component of the observed electric field is supposed to be leakage currents from DC electric railways running outside the island. Amplitude and polarization of the stray current were systematically investigated and were revealed to represent the subsurface electrical structure of the study area. Some features on the fault zone’s electrical structure have been pointed out, including: (i) an electrical boundary that corresponds to a geological one between granite (resistive) and sediments (conductive); and (ii) a low resistivity spot on the surface rupture of the earthquake fault. The structure estimated in the present study is both qualitatively and quantitatively consistent with previous resistivity surveys done using other methods pursued in the same area. It shows the validity of the ‘stray current method’ as one that is easy and uses low‐cost resistivity exploration tools in a region where the effect of artificial noise caused mainly by leakage currents from electrical railways cannot be ignored.

Geophysical variables and behavior: CIV. Power-frequency magnetic field transients (5 microtesla) and reports of haunt experiences within an electronically dense house.

Magnetic field measurements for power frequencies were measured continuously over two 24-hr. periods for a small house in which two adults who exhibited above normal occurrences of complex partial epileptic-like experiences had reported "waves of fear", tactile sensations, nightmares, apparitions, and a sensed presence. The experiences occurred within an area in which irregular amplitude modulations between 1 microT and 5 microT (50 mG) from 60-Hz sources, with durations of a few seconds to several tens of seconds, were measured. This case suggests that transient, complex temporal patterns of power-frequency magnetic fields generated by less than optimal grounding in dwellings and telluric currents may be sufficient to evoke experiences in the brains of sensitive individuals. Cultural labels, applied by the experients, then affect the explanations and expectancies for these experiences.

GEOPHYSICAL VARIABLES AND BEHAVIOR: CIV. POWER-FREQUENCY MAGNETIC FIELD TRANSIENTS (5 MICROTESLA) AND REPORTS OF HAUNT EXPERIENCES WITHIN AN ELECTRONICALLY DENSE HOUSE

Magnetic field measurements for power frequencies were measured continuously over two 24-hr. periods for a small house in which two adults who exhibited above normal occurrences of complex partial epileptic-like experiences had reported “waves of fear”, tactile sensations, nightmares, apparitions, and a sensed presence. The experiences occurred within an area in which irregular amplitude modulations between 1 microT and 5 microT (50 mG) from 60-Hz sources, with durations of a few seconds to several tens of seconds, were measured. This case suggests that transient, complex temporal patterns of power-frequency magnetic fields generated by less than optimal grounding in dwellings and telluric currents may be sufficient to evoke experiences in the brains of sensitive individuals. Cultural labels, applied by the experients, then affect the explanations and expectancies for these experiences.

Magnetic Delineation of Buried Wastes at a Church in Normal, Illinois

Graduate students enrolled in “Problems in Environmental Geology” conducted a magnetic survey of a 3.3-acre open field and parking lot immediately south of Grace Baptist Church in Normal, Illinois. The site was previously a sand and gravel quarry, then an unregulated domestic landfill. The principle objective of the survey was to have the students gain experience in planning, conducting, and reporting environmental surveys. A second objective was to better delineate the extent of the buried wastes. The wastes had previously been found in a series of ten engineering borings, but their true lateral extent was unknown.The survey was conducted with a total-intensity, proton-precession magnetometer (Geometries Model 856). This instrument measures the intensity of the magnetic field in nanoTeslas at select locations. Analysis of the Fourier transform of a single, 264-foot-long, closely spaced (2 foot) reconnaissance profile was used to determine the maximum station spacing (10 feet) and line separation (20 feet) that would adequately define the field without aliasing the data. Pre- and post-survey quality-control measurements at a base station were used to verify that the instrument was operating correctly, that the instrument operators were magnetically “clean,” and that Earth’s ambient magnetic field was stable. The surveyed magnetic total intensity was displayed as both hand-drawn and computer-generated contour maps.The magnetic survey showed several areas of intense magnetic anomalies (−700 to +2700 nanoTeslas) and other areas having a smoother magnetic field (<20 nanoTeslas). The anomalies are assumed to occur over wastes containing refractory cinders and ferrous-metal objects, an interpretation that is consistent with the engineering borings. A magnetic model composed of six finite-length polygons and one sphere was constructed to verify the feasibility of this interpretation.Areas overlying buried wastes are prone to differential settling that can compromise building foundations, pipelines, or pavements. Future development of this site should consider the distribution of the wastes as indicated by the borings and the magnetic survey. Other concerns include rusty metal and broken glass on the surface and the possibility of hazardous chemicals that could contaminate local ground water.This deceptively simple exercise, with a standard geophysical technique, involved aspects of information theory, digital data processing, potential-field theory, and a technically sophisticated instrument. Understanding the magnetic field included consideration of electrical currents in Earth’s outer core, ionospheric currents induced by extraterrestrial particles, and the complex physics of material magnetization. Also involved were the usual problems of efficiently conducting an applied field survey. For our students, the survey was a challenging exercise that convincingly demonstrated the connection between real environmental problems and the seemingly esoteric material we had been studying in the classroom.

Differential and common mode propagation in PLC low voltage networks

This paper deals with switching between differential and common mode propagation in power line carriers on low voltage distribution networks. A large field test involving several thousand items of equipment was initiated in 1995, which revealed unexpected results on network environments. An approach to the mode conversion mechanism is explained here. Moreover, experimental measurements confirm the assessment of the amplitude of the phenomena. The common mode propagation in power line carrier (PLC) systems introduces external influences from two directions: telluric currents on one hand; and significant electromagnetic field radiation on the other. Such fields have been both simulated and measured. The consequences of these phenomena are twofold. Firstly, PLC signals from LV networks cross its environment, resulting in the disturbance of others in the neighbourhood. Secondly, it makes electromagnetic compatibility an issue which cannot be neglected.