Schumann Resonance Frequency Research Articles

Three‐dimensional finite difference time domain modeling of the Schumann resonance parameters on Titan, Venus, and Mars

The conducting ionosphere and conducting surface of Titan, Venus, and Mars form a concentric resonator, which would support the possibility of the existence of global electromagnetic resonances. On Earth, such resonances are commonly referred to as Schumann resonances and are excited by lightning discharges. The detection of such resonances on other planets would give a support for the existence of the electrical discharges in the lower atmosphere on these planets. In this paper, a three‐dimensional finite difference time domain modeling for the extremely low frequency propagation is employed to study the Schumann resonance problems on Titan, Venus, and Mars. The atmospheric conductivity profiles for these studies are derived from the previously reported ionospheric models for these planets. The Schumann resonance frequencies and Q factors on these planets are calculated and are critically compared with those obtained from the previously published models.

Schumann resonance parameters calculated with a partially uniform knee model on Earth, Venus, Mars, and Titan

A partially uniform knee (PUK) model is a combination of two two‐dimensional telegraph equation (TDTE)‐based techniques: the “knee” model, which addresses the problem of approximating the knee‐like conductivity profile (on a semilogarithmic scale) of the Earth's ionosphere, and the global partially uniform day‐night model, which allows a convenient treatment of the day‐night asymmetry. Incorporation of the “knee” conductivity profile allows to overcome the shortcoming of the two‐exponential technique, widely used in extremely low frequency (ELF) work, too flat frequency dependence of quality factor in the Schumann resonance (SR) range (5–40 Hz). The PUK model predictions for Schumann resonance parameters reasonably represent observations in the SR frequency range. Propagation parameters for other planets were calculated on the basis of existing ionospheric models of the planets. To allow the approximation of structured conductivity profiles of Venus and Mars, the “knee” model was upgraded to a double‐“knee” by inserting an additional “knee” to the profile. In general, this technique allows to approximate very structured profiles by adding as many “knees” as necessary. Calculations show that the detection of Schumann resonances on Venus, Mars, and Titan is possible, though low‐quality factors on Mars and Titan imply that pronounced peaks are not to be presumed on these planets.

Diurnal variations of Schumann resonance frequency in NS and EW magnetic components

The diurnal variation of the frequency of the first Schumann resonance mode has been studied from three ELF observation sites located at Spitsbergen, the Kola Peninsula, and the Kamchatka Peninsula. The induction magnetometer measured ELF separately in two components: NS (north‐south) and EW (east‐west). The frequency variation is 0.2–0.3 Hz at all the observatories. The semidiurnal harmonics dominate in the frequency variation. The variation seems to be controlled by the local time (LT) rather than by the universal time (UT). The frequency of the NS component has maxima approximately at 0700 and 1900 LT. The diurnal variation of the frequency of the EW component reveals the antiphase behavior so that the maximum in the EW component frequency occurs at ∼0100 and 1300 LT.

Do Schumann resonance frequencies depend on altitude?

Schumann resonance frequencies are the resonance frequencies for an electromagnetic field inside the natural conducting cavity formed by the Earth's surface and its ionosphere. The spectrum peaks for the total electromagnetic energy stored inside the cavity define a unique value for each Schumann resonance. Because of the impossibility of measuring the total energy stored in the atmosphere, the experimental determination of Schumann resonances is carried out by a local measurement of the magnetic or electric field spectrum. However, peak frequencies in the amplitude of the electromagnetic field Fourier spectrum of a lightning discharge excited atmosphere may depend on height because this field depends on the atmosphere conductivity and this physical magnitude varies with height. Therefore it is reasonable to expect a slight shift between the peaks corresponding to the electric or magnetic field spectrum at a given height and those obtained by considering the total energy stored. In this paper the Earth's electromagnetic cavity is numerically modeled by using the transmission line matrix (TLM) numerical method. The altitude profile of the magnetic field spectrum remains constant from ground to 70‐km height; however, a decay between 1.5 and 4 Hz is observed for heights between 70 and 100 km, which represents a medium reduction of 10%.

Schumann resonance frequency increase during solar X‐ray bursts

Variations of the first mode Schumann resonance frequency in the Kola Peninsula and of the first and second mode frequencies in Kamchatka during seven days of March–April 2001, when the intensive solar X‐ray bursts occurred, are studied with 5 min averaging. All X‐ray bursts were accompanied by ∼0.2 Hz increase in the first mode frequency, at least in one of the magnetic components. Duration of the increases coincided with that of the bursts. For the second mode the increase (in average by ∼0.3 Hz) was registered in most events, when the ELF noise level was not very high.

Solar variations in extremely low frequency propagation parameters: 2. Observations of Schumann resonances and computation of the ELF attenuation parameter

Observations of resonant electromagnetic fields caused by global lightning activity are employed in determining the averaged parameters of the lower ionosphere. Using the two‐dimensional telegraph equation (TDTE) transmission line model described by Kuak et al. [2003], we have computed the attenuation rate of the Earth‐ionosphere waveguide from diurnal observations of the N‐S magnetic component of the ELF field performed irregularly for 6 years in the East Carpathian mountains. As the measurements were carried out during both the minimum and the maximum of the solar cycle 23 we present how solar activity influence the first Schumann resonance frequency and the attenuation rate. The analysis of all the data indicates that the first Schumann resonance frequency increases from 7.75 Hz at solar minimum to about 7.95 Hz at solar maximum while the global mean attenuation rate α at 8 Hz varies from 0.31 dB/Mm at minimum to about 0.26 dB/Mm at maximum.

A numerical simulation of Earth's electromagnetic cavity with the Transmission Line Matrix method: Schumann resonances

A numerical modeling of Earth's atmosphere is carried out by means of the Transmission Line Matrix (TLM) numerical method with the aim of calculating the Schumann resonance frequencies. The numerical results obtained are very close to the experimental ones and those obtained with the widely accepted two‐scale‐height ionospheric model, which allows us to affirm that this is a valid numerical tool for predicting the Schumann frequencies in the atmospheres of other planets and moons. The great flexibility of the TLM numerical method also allows the study of slight shifts in the Schumann resonance frequencies due to an increase in electrical conductivity at the Earth's poles, originating from high‐energy particle precipitation emitted from the Sun in conjunction with solar flares. A slight increase in the first Schumann resonance frequency is observed during these events, which is associated with a reduction in the dimensions of the electromagnetic cavity.

ELF propagation parameters for uniform models of the Earth–ionosphere waveguide

Uniform models for the Earth–ionosphere cavity are considered with particular attention to the physical properties of the ionosphere for the extremely low frequency (ELF) range. Two consistent features have long been recognized for the range: the presence of two distinct altitude layers of maximum energy dissipation within the lower ionosphere, and a “knee”-like change in the vertical conductivity profile representing a transition in dominance from ion-dominated to electron-dominated conductivity. A simplified two-exponential version of the Greifinger and Greifinger (1978) technique widely used in ELF work identifies two slopes in the conductivity profile and, providing accurate results in the ELF communication band (45– 75 Hz ), simulates too flat a frequency dependence of the quality factor within the Schumann resonance frequency range (5– 40 Hz ). The problem is traced to the upward migration, with frequency increasing, of the lower dissipation layer through the “knee” region resulting in a pronounced decrease of the effective scale height for conductivity. To overcome this shortcoming of the two-exponential approximation and still retain valuable model analyticity, a more general approach (but still based on the Greifinger and Greifinger formalism) is presented in the form of a “knee” model whose predictions for the modal frequencies, the wave phase velocities and the quality factors reasonably represent observations in the Schumann resonance frequency range.

Decrease of the first Schumann resonance frequency during solar proton events

The variations of the first‐order Schumann resonance frequency in Kola peninsula are studied for four solar proton events on November 4 and 6, 1997 and on May 2 and May 6, 1998. It is found that the frequency decreases by about 0.15 Hz during the peaks of the proton penetrations. Such a decrease is in agreement with modeling calculations. A very intensive solar X ray burst preceding the proton flare on November 6 caused an increase of the resonance frequency. The decrease of amplitude about of 0.2 pT and the decrease of the resonance bandwidth about of 0.2 Hz are observed in the November events.

Changes of the first Schumann resonance frequency during relativistic solar proton precipitation in the 6 November 1997 event

Abstract. The variations of the first mode of Schumann resonance are analyzed using data from Kola peninsula stations during the solar proton event of 6 November 1997. On this day the intensive flux of energetic protons on GOES-8 and the 10% increase of the count rate of the neutron monitor in Apatity between 1220 and 2000 UT were preceded by a solar X-ray burst at 1155 UT. This burst was accompanied by a simultaneous increase of the Schumann frequency by 3.5%, and the relativistic proton flux increase was accompanied by 1% frequency decrease. These effects are explained by changes of the height and dielectric permeability of the Earth-ionosphere cavity.Key words. Ionosphere (ionospheric disturbances; solar radiation and cosmic ray effects) · Radio science (ionospheric propagation)

Changes of the first Schumann resonance frequency during relativistic solar proton precipitation in the 6 November 1997 event

Changes of the first Schumann resonance frequency during relativistic solar proton precipitation in the 6 November 1997 event

Anomalous behavior of Schumann resonances during the transition between 1995 and 1996

Anomalous behavior of Schumann resonance (SR) parameters is presented in interannual relations for the first time. The mean daily intensity of the first three SR modes measured in the vertical electric component at the Nagycenk Observatory (47.6°N, 16.7°E), Central Europe, was significantly higher in December 1995 and January 1996 than in the same months 1 year before. The largest relative SR intensity deviations occurred in the third part of December 1995 and in the evening hours (2000–2200 UT), when the lightning activity of the South American thunderstorm region is the most intense. In January 1996 the largest relative SR intensity deviations appeared in the early morning hours (0000–0030 UT), when the worldwide thunderstorm activity is at a minimum. This result suggests that a lightning activity in the Pacific region was not as sparse in January 1996 as it was in January 1995. The time variation of the maxima of the SR intensity ratios indicates a westward propagation with trade wind speeds of about 2 to 8 m s−1 from the end of December 1995 about to the end of January 1996. The anomalous SR intensity in December 1995 is attributed to a small increase in the surface air temperature (about 0.2°C) and to the extension of the thunderstorm region indicated by the SR frequency range variation. It is also suggested that this warmer air mass was advected by easterlies from the end of December 1995 over the cooler Pacific in January 1996 causing more intense lightning activity there.

Natural ELF Electromagnetic Pulses

An interest towards monitoring the natural electromagnetic pulse radio signals re-appeared recently stimulated by the attempts of location the distant powerful lightning strokes that cause optical emissions in the upper atmosphere. Such a luminous structure over a thunderstorm cell may reach the 95 km altitude. Optical events were classified as 'red sprites', 'elves', and 'blue jets', see [1-3] and reference therein. The observations were performed over the USA territory, and the co-ordinates of causative strokes were established with the National Lightning Detection Network. To cover a wider territory, an application of the Schumann resonance frequency range had been suggested, namely, the frequencies from a few Hz to a hundred Hz [4]. The slow tail technique may be applied as well at the distances to a few thousands km, see [5] and reference therein. Slow tail atmospherics are observed at the frequencies from a few hundred to a few thousand Hz. Both the measurement techniques are not new, these were developed and used actively in 60s-70s. A zero order mode or TEM wave propagates in the Earth-ionosphere waveguide at the frequencies below 1.6-1.7 kHz. The first transverse resonance occurs at the above frequency [6], the particular value depends on the ambient day- or night-time propagation conditions. The wave attenuation factor is small below the 100 Hz frequency, enabling a radio wave to travel around the Earth's circumference. The global or Shumann resonance (SR) is observed then. When the frequency increases, the wave absorption grows, and the 'round-the-world' waves become so small that the resonance vanish, and the spectra become smooth. This was one of a reasons why the Q-bursts in the SR range and the slow tail atmospherics that are observed at higher frequencies were treated separately. The goal of the present study is an analysis of the model solution within the whole the extremely low frequency (ELF) band. We apply a well-known frequency domain solution for the wave travelling in the spherical Earth-ionosphere cavity. The time dependent field components are obtained with the numerical Fourier transform. Within such an approach, any further development of the known theory is unnecessary, and the field distribution over the frequency-distance plane are obtained from the unified positions.

Study of the annual changes of global lightning distribution and frequency variations of the first Schumann resonance mode

From the yearly averaged diurnal variations of the first Schumann resonance frequency, corresponding changes in the area covered by global lightning were calculated and then compared with optical observations made by satellite 11 years later. The data observed are characterized by the high cross-correlation coefficient. The conclusion is that Schumann resonance frequency variations are an indicator of the thunderstorm distribution over the globe.

Gravitational-to-electromagnetic wave conversion in electrostatic field of earth-ionosphere resonator

The conversion of a plane gravitational wave into electromagnetic radiation in the presence of the fair-weather static electric field of the earth-ionosphere resonator is examined. The spatial and frequency characteristics of the induced electromagnetic field of the earth-ionosphere cavity are studied in the range of Schumann resonance frequencies (f=10–100 Hz). Numerical estimates are obtained for the amplitudes of the electromagnetic fields, and the possibilities of a natural gravitational-wave detector are considered.

Resistivity structure of Izu-Oshima volcano revealed by the ELF-VLF magnetotelluric method.

The VLF and ELF magnetotelluric (MT) methods have been applied to study the electrical resistivity distribution in the Izu-Oshima volcano. We utilized a 17.4kHz artificial electromagnetic signal for the VLF method, and three fundamental Schumann resonance frequencies for the ELF method. Measurements were made in 1984 and 1985 at 57 sites including 30 on the central caldera floor, and one-dimensional resistivity models were determined from the results. The modeling results clearly indicate the dominance of a water reservoir beneath the caldera at the depth of a few hundred meters above the sea level.On the crater floor of the central cone Mihara-yama, measurements were carried out at four sites. The result shows a very shallow conductor with a resistivity of less than 10Ω·m. We also found that the edifice of Mihara-yama tends to be more conducting in the southern part than in the northern part, extending in the east-west direction. The important thing is that, within the one-dimensional approximation, this anomalously conducting layer exists only 200-300m below the crater floor. We concluded this conducting layer directly reflects the present thermal activity in the central cone of Mihara-yama. Furthermore, the depth of the conducting layer tends to be shallow at the northern and southern parts of the caldera rim. This shows a peculiar feature of the groundwater distribution beneath the caldera rim.

A portable ELF-MT system for shallow resistivity sounding

In view of recent extensive investigation of shallow resistivity structure for active fault studies and geothermal exploration, we developed a portable magnetotelluric (MT) system for the extremely low frequency (ELF) range. The system aims primarily at making real-time analyses of MT data at the so-called Schumann resonance frequencies of ∼ 8, 14 and 20 Hz. Calculations of the apparent resistivity, the phase, etc. are made by a small HC-20 computer, which also controls data acquisition. We made performance tests of this system and compared the results with those derived by the conventional method using the large computer at our computer center. The stacking number of 30 for Fourier transform stacking turned out to be sufficient to obtain results comparable with those by the conventional method. The time required for this processing is ∼ 15 min. This system can also be used for continuous monitoring of time-dependence of shallow crustal resistivity, particularly for earthquake prediction studies.

Schumann resonance frequency variations during sudden ionospheric disturbances

Fluctuations of the fundamental and harmonic frequencies of the Schumann (earth-ionosphere cavity) resonances measured near Tromsø, Norway, on 28 March 1979 are examined on a timescale of ≲ 20 minutes. Their relationships with two sudden ionospheric disturbance events and one other geophysical event is investigated. The experimentally observed frequency variations are, in some cases, at variance with the theoretical predictions of Madden and Thompson (1965).

Schumann resonances and electrical conductivity of the atmospher and lower ionosphere—I. Effects of conductivity at various altitudes on resonance frequencies and attenuation

Three realistic, continuous ionospheric conductivity profiles and an idealized model of the ionosphere, consisting of three discrete layers, are used to investigate the effects of conductivity at altitudes from ground level to 100 km upon the Schumann resonance frequencies and ELF attenuation. The ultimate objective is to infer a conductivity profile from resonance frequencies and cavity Q measured at ground level which will be done in Part II. In Part I it is shown that the dominant effects are due to the region between roughly 40 km and 60 km where the ratio of conduction current to displacement current is 0.01 ≲ [ σ/( ωϵ 0)] ≲ 40. A finite average conductivity σ a of the atmosphere below approximately 40 km altitude must be considered for accurate evaluation of wave attenuation or cavity Q. Variations in σ a can have the same effect upon attenuation as possible changes in ionospheric conductivity in the 70–80 km altitude range.

Experimental investigations of Schumann resonance frequencies

The Schumann cavity resonances are excited by thunderstorms in the Earth-ionosphere cavity. There are, however, many cases in which data analyses are difficult because of the world wide nature of the phenomenon. This paper describes the results of observations made by the use of a solenoidal coil antenna. Day-to-day variations of the resonance frequency and the averaged diurnal variations are discussed with regard to solar ionizing radiation, solar zenith angle and geomagnetic disturbances.