Earth's Electromagnetic Environment Research Articles

Monitoring of Space and Earth electromagnetic environment by MAGDAS project: Collaboration with IKIR - Introduction to ICSWSE/MAGDAS project

For study of coupling processes in the Solar-Terrestrial System, International Center for Space Weather Science and Education (ICSWSE), Kyushu University has developed a real time magnetic data acquisition system (the MAGDAS project) around the world. The number of observational sites is increasing every year with the collaboration of host countries. Now at this time, the MAGDAS Project has installed 78 real time magnetometers – so it is the largest magnetometer array in the world. The history of global observation at Kyushu University is over 30 years and number of developed observational sites is over 140. Especially, Collaboration between IKIR is extended back to 1990's. Now a time, we are operating Flux-gate magnetometer and FM-CW Radar. It is one of most important collaboration for space weather monitoring. By using MAGDAS data, ICSWSE produces many types of space weather index, such as EE-index (for monitoring long tern and shot term variation of equatorial electrojet), Pc5 index (for monitoring solar-wind velocity and high energy electron flux), Sq-index (for monitoring global change of ionospheric low and middle latitudinal current system), and Pc3 index (for monitoring of plasma density variation at low latitudes). In this report, we will introduce recent development of MAGDAS/ICSWSE Indexes project and topics for new open policy for MAGDAS data will be also discussed.

Magnetic clouds and origins in STEREO era

AbstractWhen a coronal mass ejection (CME) encounters the Earth, the Earth's electromagnetic environment is disturbed, especially when it is a magnetic cloud (MC) with enhanced, steady, and long‐lasting southward field. The speed and the magnetic field of an MC are the two important properties for its geoeffectiveness. The correspondence between a CME and its resulting MC is not straightforward, partly due to the CME velocity and the complications during propagation through corona and the solar wind. From 2007 to 2012, we have three observing points at 1 AU near the ecliptic plane (ACE and STEREO A and B). We search for MC events encountered at one of the three observers and study the statistics independently and in comparison. We found that the annual number of MCs at each receiver varies significantly and the temporal variation at each receiver does not always follow the solar activity level. The speed and the magnetic field strength of the MCs do vary with the solar activity level. The polarity of MC magnetic field at ACE and STEREO also shows large fluctuations. We have also identified the CME and solar activity sources for the L1 MC events. STEREO SECCHI images served critical roles in the determination of the CMEs both in solar quiet times and active times. We found that halo CMEs are not necessarily good indicators for receiving MCs. Further studies of CME initial velocity and the propagation through the heliosphere are needed in order to improve our space weather forecasting capability.

Scaling law describes Earth's electromagnetic environment

The electromagnetic environment surrounding Earth, including the geomagnetic field and atmospheric electric fields, varies on all time scales, but this frequency dependence has not been well studied. Analyzing observations compiled from several published sources,Füllekrug and Fraser‐Smith found that the energy density of the electromagnetic fields at the surface of the Earth follows a simple, fundamental scaling law: The energy density of the fields at a given frequency is inversely proportional to the square of the frequency. This relationship extends over a wide range of frequencies—16 orders of magnitude. The authors note that this is somewhat surprising, given the many different processes that cause electromagnetic field variations, including lightning discharge in the atmosphere, geomagnetic storms in the ionosphere, and many other electromagnetic effects, such as sprites in the middle atmosphere.

The Earth's electromagnetic environment

[1] It is found that the energy density of electromagnetic fields at the surface of the Earth follow a scaling law that extends over ∼16 orders of magnitude from ∼10−9 Hz to ∼107 Hz. The temporal variability of the field can be described with an ∼1/f2, or Brownian, noise power spectrum which reflects the superposition of numerous transient source processes. To the best of our knowledge, the spectral extent of this straightforward scaling law is unparalleled and outperforms any other scaling law in physics which describes a time dependent observable. The frequency dependence of the energy density can be approximated with the analytic description u(f) = u0(f0/f)2 where u0 = 10−16 Jm−3Hz−1, f0 = 1 Hz is a scaling constant, and f is the frequency of the electromagnetic field. The corresponding frequency dependence of the magnetic field is B(f) = B0(f0/f) where B0 = 10−11 T/Hz1/2.

Electromagnetic models of the lightning return stroke

Lightning return‐stroke models are needed for specifying the source in studying the production of transient optical emission (elves) in the lower ionosphere, the energetic radiation from lightning, and characterization of the Earth's electromagnetic environment, as well as studying lightning interaction with various objects and systems. Reviewed here are models based on Maxwell's equations and referred to as electromagnetic models. These models are relatively new and most rigorous of all models suitable for computing lightning electromagnetic fields. Maxwell's equations are numerically solved to yield the distribution of current along the lightning channel. Different numerical techniques, including the method of moments (MoM) and the finite difference time domain (FDTD) method, are employed. In order to achieve a desirable current‐wave propagation speed (lower than the speed of light in air), the channel‐representing wire is embedded in a dielectric (other than air) or loaded by additional distributed series inductance. Capacitive loading has been also suggested. The artificial dielectric medium is used only for finding the distribution of current along the lightning channel, after which the channel is allowed to radiate in air. Resistive loading is used to control current attenuation with height. In contrast with distributed circuit and so‐called engineering models, electromagnetic return‐stroke models allow a self‐consistent full‐wave solution for both lightning‐current distribution and resultant electromagnetic fields. In this review, we discuss advantages and disadvantages of four return‐stroke channel representations: a perfectly conducting/resistive wire in air, a wire embedded in a dielectric (other than air), a wire in air loaded by additional distributed series inductance, and a wire in air having additional distributed shunt capacitance. Further, we describe and compare different methods of excitation used in electromagnetic return‐stroke models: closing a charged vertical wire at its bottom with a specified grounded circuit, a delta‐gap electric field source, and a lumped current source. Finally, we review and compare representative numerical techniques used in electromagnetic modeling of the lightning return stroke: MoMs in the time and frequency domains and the FDTD method. We additionally consider the so‐called hybrid model of the lightning return stroke that employs a combination of electromagnetic and circuit theories and compare this model to electromagnetic models.

Surveying the Earth's electromagnetic environment from space

The scientific objectives of DEMETER (Detection of Electro‐Magnetic Emissions Transmitted from Earthquake Regions) are the detection and characterization of the ionospheric perturbations associated with natural phenomena (such as earthquakes, volcanic eruptions, tsunamis) or with anthropogenic activities. To achieve these objectives, the microsatellite, which was launched at the end of June 2004, surveys the Earth's electromagnetic environment. DEMETER is the first in the Myriade series of microsatellites developed by the Centre National d'Etudes Spatiales (CNES, France) for lowcost science missions.

Preliminary report on the effect of elf magnetic pulsations on human subjects

During the last decade considerable interest has been evinced by scientists on the possible control of earth's electromagnetic environment on human physiology. The present paper discusses the effects of oscillatory magnetic fields in the extremely low frequency range on electrophysiological and biochemical parameters in human subjects. Normal subjects and practitioners of Yoga and meditation were exposed to sinusoidally oscillating magnetic fields in the frequency range of 0.01 to 10 Hz and with amplitudes of ±5 and ±50 nT generated inside a special controlled magnetic field enclosure with the subjects' heads oriented in the four cardinal directions and also in sitting posture, and against ambient magnetic fields of about 40000 nT (local geomagnetic field) and half this value (or 20000 nT). The ECG, finger blood flow and respiration were recorded continuously on a polygraph. The EEG was also recorded on an 8-channel machine with split-up of waves into alpha, beta, delta and theta components. Biochemical assays were carried out on the blood and urine. Certain decisive changes were observed in the electrophysiology, such as, for instance, a sharp inhibition of the brain's electrical activity with the head towards the North and, in contrast, an accentuation of activity in the East orientation. Alterations in the levels of metabolites of catechol and indole amines were seen in the North orientation.

Effect of magnetic micropulsations on the biological systems--a bioenvironmental study.

During the last decade considerable interest has been evinced by scientists on the possible influence of earth's electromagnetic environment on human and animal physiology. While some studies on this topic have been reported from high magnetic latitudes — USSR and central Europe — no work has been done in very low latitude and equatorial regions. The present study, undertaken to fill this gap, has been carried out at the low latitude of Madras (Magnetic Dip ≅ 10°). Pulsating magnetic fields in the frequency range of 0.01 Hz to 20 Hz and with amplitudes of ±5 and ±50 gamma were impressed on test animals, normal human subjects and Yoga practitioners lying supine inside a 4-member Fanselau-Braunbeck coil system with the heads oriented in the four cardinal directions with respect to earth's magnetic field. The entire set of exposures of the test animals and humans was given under two ambient magnetic fields namely, against full local geomagnetic field of about 40,000 gamma and half this value. In the animals ECG, EEG, Tail Blood Flow and Respiration were recorded continuously on a polygraph. The biochemical tests carried out were postprandial blood sugar, serum cholesterol and plasma cortisol. Neurochemical assays of Noradrenaline, Adrenaline, Dopamine, Serotonin and 5 Hydroxy Indole Acetic acid were done on the brain tissue, myocardium and adrenal glands, immediately after complete set of exposures of the animals in all four orientations. Motor activity and rectal temperature were also noted before and after the exposures. The ‘Control’ animals were also subjected to exactly the same investigations as the test animals without, however, exposing them to the magnetic fields. These observations revealed some decisive changes in certain parameters for certain frequencies of the impressed field and also in specific orientations of the test animals. Similar studies carried out on normal human subjects and practitioners of Yoga and Meditation, also showed certain decisive changes in the electrophysiology, neurochemistry and biochemistry when oriented to North and East. The North orientation appeared to induce inhibition of brain electrical activity and associated neurochemical and biochemical changes, whereas the East orientation showed a response of calm, blissful alertness.

The Earth's magnetosphere

The growth of satellite observations over the last 15 years, together with increasingly sophisticated ground-based measurements, has brought the study of Earth's electromagnetic environment to a new era of development. This study has grown to a broad discipline that overlaps magnetism, astrophysics and plasma physics. Important understandings have been achieved in many areas including auroral phenomena, distributions and interactions of plasmas and waves in the magnetosphere, the physics of wave–energetic-particle interactions, and the identification of magnetic-field-aligned currents.