Earth-ionosphere Cavity Research Articles

Parametric excitation of an extremely low-frequency radio pulse by an extragalactic gamma-ray burst on December 27, 2004

We simulate an electromagnetic pulse excited by a sharp descent of the charged upper wall of the Earth–ionosphere cavity. The ionosphere descent by 20 km was detected over the dayside Earth’s hemisphere during a giant extragalactic gamma-ray burst in the constellation of Sagittarius (SGR 1806–20). We show that a sharp change in the ionosphere altitude can cause a discrete pulse of extremely low-frequency radiation with the spectrum having some specific features and the amplitude significantly exceeding the natural regular noise background. The time of arrival of the radio pulse to an observer coincides with the gamma-burst time.

Local High-Resolution Technique in FDTD Modeling of ELF Propagation in the Earth–Ionosphere Cavity

In this letter, a local high-resolution technique (LHRT) of three-dimensional finite-difference time-domain (3D-FDTD) method is presented for the extremely low-frequency (ELF) electromagnetic (EM) wave propagation in the Earth-ionosphere cavity. This new model is useful for the analysis of the ELF EM wave propagating in a specific region, where the required space interval of the grid-cell is extremely fine. Once the length of the required space interval in the specific region and the cutoff frequency of the source are determined, the model of Earth-ionosphere cavity can be established automatically. It is verified that the simulation results of the new technique are as accurate as those of the traditional methods.

Ground‐based detection of sprites and their parent lightning flashes over Africa during the 2006 AMMA campaign

AbstractSprites have been detected in video camera observations from Niger over mesoscale convective systems in Nigeria during the 2006 AMMA (African Monsoon Multidisciplinary Analysis) campaign. The parent lightning flashes have been detected by multiple Extremely Low Frequency (ELF) receiving stations worldwide. The recorded charge moments of the parent lightning flashes are often in excellent agreement between different receiving sites, and are furthermore consistent with conventional dielectric breakdown in the mesosphere as the origin of the sprites. Analysis of the polarization of the horizontal magnetic field at the distant receivers provides evidence that the departure from linear magnetic polarization at ELF is caused primarily by the day–night asymmetry of the Earth–ionosphere cavity. Copyright © 2009 Royal Meteorological Society

Observation and modeling of the Earth-ionosphere cavity electromagnetic transverse resonance and variation of the D-region electron density near sunset

In the frame of the African Monsoon Multidisciplinary Analyses campaign, measurements of very low frequency electric fields were performed onboard a stratospheric balloon launched on 7 August 2006 from Niamey, Niger. During flight, numerous sferics were observed associated to lightning from active convective cells a few hundred kilometers from the balloon. Lightning data analysis shows the transverse mode mean frequency of the Earth‐ionosphere cavity decreasing from ∼2.4 to 2 kHz over a period of 1 h about sunset. The observed change of the transverse resonance near dusk can be fairly reproduced by an electromagnetic wave propagation model, which takes into account the D‐region electron density variation predicted by the International Reference Ionosphere model.

Analysis of the Atmospheric Electric Circuit using the Finite Element Method

This study concerns the electrical properties of the Earth's lower atmosphere. A theoretical description of the terrestrial global circuit is presented. An electrostatic model based on the finite element technique is used to investigate the following parameters of the Earth-ionosphere cavity: (i) energy storage in different regions; (ii) variation with height of the electric field and space charge. The modeled domain is bound by two concentric conductive spheres to represent the Earth's surface and the lower ionosphere; a set of intermediate concentric conductive spheres is employed to discretize the inner space. The sources of energy are defined by specifying the electric potential of all conductive spheres; these potentials are obtained from the vertical electric field profile proposed by Gish. The axisymmetric problem provides three-dimensional information about the various parameters. Numerical calculations of the different parameters are compared to analytical predictions of the Gish model and show a very good correlation.

Bounds on Lorentz andCPTviolation from the Earth-ionosphere cavity

Electromagnetic resonant cavities form the basis of many tests of Lorentz invariance involving photons. The effects of some forms of Lorentz violation scale with cavity size. We investigate possible signals of violations in the naturally occurring resonances formed in the Earth-ionosphere cavity. Comparison with observed resonances places the first terrestrial constraints on coefficients associated with dimension-three Lorentz-violating operators at the level of 10^{-20} GeV.

An improved Lorentzian technique for evaluating resonance characteristics of the Earth-ionosphere cavity

The effectiveness of various formulations of the Lorentzian procedure for estimating Schumann resonance (SR) characteristics of the Earth-ionosphere waveguide from transient electromagnetic signals is tested in the limits of a simplified, spherically uniform model of the resonator. It is shown that the major improvement, in comparison with the “classic” Lorentzian formulation, is achieved by consideration of the intra-modal phase interference. The effect of the “limited frequency dispersion” inherent in the “classic” Lorentzian approach – that is of substantial importance at the lowest SR modes – can be effectively neutralized by interpolating the values for the propagation parameter between the adjacent modal frequencies. Several practical aspects of applying the Lorentzian procedure to transient signals are also discussed.

Examples of the zeroth theorem of the history of science

The zeroth theorem of the history of science (enunciated by E. P. Fischer) and widely known in the mathematics community as Arnol’d’s principle states that a discovery (rule, regularity, or insight) named after someone often did not originate with that person. I present five examples from physics: the Lorentz condition ∂μAμ=0 defining the Lorentz gauge of the electromagnetic potentials, the Dirac delta function δ(x), the Schumann resonances of the Earth-ionosphere cavity, the Weizsäcker–Williams method of virtual quanta, and the Bargmann, Michel, and Telegdi equation of spin dynamics. I give sketches of both the actual and reputed discoverers and quote from their “discovery” publications.

Reply to comment by A. P. Nickolaenko and M. Hayakawa on “Sprite lightning heard round the world by Schumann resonance methods”

Reply to comment by A. P. Nickolaenko and M. Hayakawa on “Sprite lightning heard round the world by Schumann resonance methods”

Schumann Resonances as a Means of Investigating the Electromagnetic Environment in the Solar System

The propagation of extremely low frequency (ELF, 3 Hz to 3 kHz) radio waves and resonant phenomena in the spherical Earth-ionosphere cavity has been studied for almost fifty years. When such a cavity is excited by naturally occurring broadband electromagnetic radiation, resonances can develop if the equatorial circumference is approximately equal to an integral number of wavelengths of the propagating electromagnetic waves; these are termed Schumann resonances. They provide information not only about thunderstorm and lightning activity on the Earth, and their relation to climate, but also on the properties of the low ionosphere. Similar investigations can be performed for any other planet or satellite, provided that it has an ionosphere.

Universal and local time components in Schumann resonance intensity

Abstract. We extend the technique suggested by Sentman and Fraser (1991) and discussed by Pechony and Price (2006), the technique for separating the local and universal time variations in the Schumann resonance intensity. Initially, we simulate the resonance oscillations in a uniform Earth-ionosphere cavity with the distribution of lightning strokes based on the OTD satellite data. Different field components were used in the Dayside source model for the Moshiri (Japan, geographic coordinates: 44.365° N, 142.24° E) and Lehta (Karelia, Russia, 64.427° N, 33.974° E) observatories. We use the extended Fourier series for obtaining the modulating functions. Simulations show that the algorithm evaluates the impact of the source proximity in the resonance intensity. Our major goal was in estimating the universal alteration factors, which reflect changes in the global thunderstorm activity. It was achieved by compensating the local factors present in the initial data. The technique is introduced with the model Schumann resonance data and afterwards we use the long-term experimental records at the above sites for obtaining the diurnal/monthly variations of the global thunderstorms.

Electromagnetic field measurements in ULF-ELF-VLF [0.001 Hz–100 KHz] bands

Abstract. We are reporting the technological and scientific objectives of the MEM project. The MEM project has been activated in the INGV Observatory of L'Aquila to create in Central Italy a network of observatories in order to monitoring the electromagnetic signals in the frequency band [0.001 Hz–100 kHz]. Some examples of the instrumentation developed in the frame of the project are reported. An innovative technique, based on the wide band interferometry is proposed to obtain detailed information concerning the several detected electromagnetic sources. Moreover, data from each station will be elaborated to investigate different sectors as the structure of ground electric conductibility, the electromagnetic phenomena connected with seismic activity, the separation of the electromagnetic fields originated in the Earth's interior and the electromagnetic phenomena originated in the magnetosphere, in the ionosphere and in the Earth-ionosphere cavity.

Spherical harmonic series solution of fields excited by vertical electric dipole in earth-ionosphere cavity

The spherical harmonic series expression of electromagnetic fields excited by ELF/SLF vertical electric dipole in the spherical earth-ionosphere cavity is derived when the earth and ionosphere are regarded as non-ideal conductors. A method of speeding numerical convergence has been presented. The electromagnetic fields in the cavity are calculated by this algorithm, and the results show that the electromagnetic fields between the earth and the ionosphere are the sum of two traveling waves in the SLF band. Moreover, the results are in complete agreement with that of the well-known spherical second-order approximation in the SLF band. The electromagnetic fields in the cavity are a type of standing wave in the ELF band and the variation of the amplitude versus frequency coincides with Schumann’s resonance.

Global FDTD Maxwell's Equations Modeling of Electromagnetic Propagation From Currents in the Lithosphere

Electromagnetic wave propagation from electric currents within the Earth's crust is investigated using a three-dimensional finite-difference time-domain (FDTD) full-vector Maxwell's equations model of the global Earth-ionosphere cavity. The FDTD model employed extends from km below sea level to an altitude of km, and can account for arbitrary horizontal as well as vertical geometrical and electrical inhomogeneities and anisotropies of the ionosphere, lithosphere, and oceans. Using this model, the surface horizontal magnetic field is calculated for different depths and orientations of an electric current occurring below the epicenter of the 1989 Loma Prieta earthquake. Results show that the alignment and depth of the electric current within the Earth's crust yields significant differences for the calculated surface magnetic field time-waveforms and spectra. Further, it is found that EM wave phenomena measured at the Earth's surface due to electric currents buried in the Earth's crust will only have significant spectra below 1 Hz.

A case study on the ELF characterization of the Earth–ionosphere cavity: Forecasting the Schumann resonance intensities

Schumann Resonances (SR) are the electromagnetic (EM) phenomena which occur in the cavity formed by the conducting Earth and the ionosphere, with peak mode frequencies close to 8, 14, 20, 26, 32 Hz, etc. [Price, C., Melnikov, A., 2004. Diurnal, seasonal and inter-annual variations in the Schumann resonance parameters. Journal of Atmospheric and Solar-Terrestrial Physics 66, 1179–1185]. The spectral characteristics of the SR modes are defined by their resonant mode amplitudes, center frequencies and half-widths [Price, C., Melnikov, A., 2004. Diurnal, seasonal and inter-annual variations in the Schumann resonance parameters. Journal of Atmospheric and Solar-Terrestrial Physics 66, 1179–1185]. The objective of this work is two fold: (i) to investigate the characteristics of SR parameters obtained at Şarköy in Turkey and (ii) to model the dynamical characteristics of the SR processes by forecasting the first SR mode power values using a neural network (NN) model. The NN model is revised version of the METUNN [Tulunay, Y., Tulunay, E., Senalp, E.T., 2004a. The neural network technique—1: a general exposition. Advances in Space Research 33, 983–987].

Peculiar transient events in the Schumann resonance band and their possible explanation

Superimposed on the continuous Schumann resonance (SR) background in the extremely low frequency (ELF) band, transient signals (e.g. bursts) can be observed, which originate from intense lightning discharges occurring at different locations on the globe. From the many transients that were observed at the Astronomical and Geophysical Observatory (AGO) of Comenius University near Modra, western Slovakia, in the vertical electric field component mainly during May and June of 2006, a peculiar group of events could be recognized. According to the waveform analysis, these peculiar events in most cases consist of two overlapping transients with a characteristic time difference of 0.13–0.15 s between the onsets. On the other hand, the spectrum of these peculiar transients showed discernible SR peaks for higher modes as well ( n>7). The same events could be found in the records of the Széchenyi István Geophysical Observatory of the Geodetic and Geophysical Research Institute of the Hungarian Academy of Sciences near Nagycenk, Hungary (NCK). The natural origin of the peculiar events was verified from the NCK data and the source location was determined from the second transient. The results suggest that the two consecutive transients originated in the same thunderstorm. Furthermore, the phase spectrum analysis indicates that the sources have coherently excited the Earth-ionosphere cavity. These findings seem to support the idea that electromagnetic waves orbiting the Earth might trigger lightning discharges. The possibility that electromagnetic waves may trigger discharges was first considered by Nikola Tesla.

A Review of Progress in FDTD Maxwell's Equations Modeling of Impulsive Subionospheric Propagation Below 300 kHz

Wave propagation at the bottom of the electromagnetic spectrum (below 300 kHz) in the Earth-ionosphere waveguide system has been an interesting and important area of investigation for the last four decades. Such wave propagation is characterized by complex phenomena involving nonhomogeneous and anisotropic media, and can result in resonances of the entire Earth-ionosphere cavity. In the spirit of this Special Issue, the goal of this paper is to call attention to emerging finite-difference time-domain computational solutions of Maxwell's equations for wave propagation below 300 kHz which promise to complement and extend previous analyses by pioneers such as Profs. Wait and Felsen. The following topical areas are discussed: long-range two-dimensional propagation, lightning sources and radiation, global propagation, Schumann resonances, hypothesized pre-seismic lithosphere sources and radiation, detection of deep underground resource formations, and remote sensing of localized ionospheric anomalies. We conclude with a prospectus for future research, especially in incorporating the physics of the anisotropic, nonhomogeneous magnetized plasma in a global planetary ionosphere.

A new numerical model for the simulation of ELF wave propagation and the computation of eigenmodes in the atmosphere of Titan: Did Huygens observe any Schumann resonance?

The propagation of extremely low frequency (ELF) electromagnetic waves in the Earth's ionospheric cavity and the associated resonance phenomena have been extensively studied, in relation with lightning activity. We perform a similar investigation for Titan, the largest moon of Saturn. There are important differences between Earth and Titan, as far as the cavity geometry, the atmospheric electron density profile, and the surface conductivity are concerned. We present an improved 3D finite element model that provides an estimate of the lowest eigenfrequencies, associated quality factors ( Q-factors), and ELF electric field spectra. The data collected by the electric antenna of the Permittivity, Waves, and Altimetry (PWA) instrument reveals the existence of a narrow-band signal at about 36 Hz during the entire descent of Huygens upon Titan. We assess the significance of these measurements against the model predictions, with due consideration to the experimental uncertainties.

Magnetic polarization of the Schumann resonances: An asymptotic theory

Horizontal components of extremely low-frequency (ELF) fields in the gyrotropic Earth–ionosphere cavity are expressed through the fields of an isotropic cavity. A linear approximation of the perturbation method with respect to two small parameters is used. These are the impedance z 0 of the isotropic ionosphere and the ratio γ≡ z 2/ z 1 of the off-diagonal to diagonal elements of the surface impedance matrix of the gyrotropic ionosphere. It is shown that the effect of splitting of the Schumann resonance frequencies caused by the existence of the d.c. geomagnetic field results in an “apparent” angular shift of all ground-based sources of ELF radiation toward the geographic West (“refraction of ELF fields in the gyrotropic Earth–ionosphere cavity”) and excitation of an elliptical magnetic polarization. An analytical relation for the mentioned phenomena is derived. Explicit expressions for polarization characteristics of the electromagnetic ELF noise excited by an arbitrary number of equatorial thunderstorm centers are obtained. Expected values of the “apparent” angular shift for these sources are estimated. Analysis of the estimated magnitudes shows that locations of thunderstorm centers and isolated Q-bursts determined with the use of multi-component ELF measurements should be corrected to exclude the “gyrotropic refraction” effect. Equations to calculate the necessary corrections are presented. The results are generalized to the case of an arbitrary latitudinal location of the sources.

Nano- and microscale particles and global electromagnetic resonances in the Earth-ionosphere cavity

The influence of nano-and microscale particles (dust grains) on the global electromagnetic (Schumann) cavity has been studied in the context of two possible mechanisms. First, the presence of charged microscale particles in the ionospheric plasma modifies the dispersion properties of the upper boundary of the Schumann cavity and, thus, affects its eigenfrequencies and quality factor. Second, there is a relation between the dust concentration in the atmosphere and lightning discharges, which excite Schumann resonances. Therefore, dust grains can enhance the energy pumping of the cavity, thereby increasing the amplitude of electromagnetic oscillations in it.