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Nickolaenko A.P.,Ukrainian Academy of Sciences | Hayakawa M.,Hayakawa Institute of Seismo Electromagnetics Co. | Hayakawa M.,University of Electro - Communications
Radio Science

Spectra and the waveforms are computed of the pulsed radio signals arriving from different distances to an observer in the Earth-ionosphere cavity with the single-scale exponential profile of air conductivity. The data were obtained for the cavity with exceptionally small losses. Spectra are compared of the signals in the realistic and an idealistic Earth-ionosphere cavities. The waveforms are computed for such cavities and the pulse propagation velocities are evaluated. Studies of the Schumann resonance started from the ideal cavity model. Subsequent works dealt with the realistic propagation parameters and the ionosphere models on the Earth and other planets. However, the case of small losses is missing in the literature. We model ELF radio signals in such a cavity and demonstrate their noticeable distinctions from the customary records. In particular, the sinusoidal signals do not appear in the cavity with small losses, and instead, we obtain the sharp and large pulses. Computations show that the waveform propagating in the spherical cavity expands in time and reduces in amplitude. The time domain pulsed amplitudes were found at the source antipode and at the source point for the round-the-world wave. The latter becomes rather small even in the cavity with minor losses, so that autotriggering is unrealistic of a consecutive lightning discharge by the round-the-world echo even in a cavity with minor losses. Key Points ELF waveforms are computed in the Earth-ionosphere cavity with small losses ©2014. American Geophysical Union. All Rights Reserved. Source

Ohta K.,Chubu University | Izutsu J.,Chubu University | Schekotov A.,Russian Academy of Sciences | Hayakawa M.,University of Electro - Communications | And 2 more authors.
Radio Science

The ULF/ELF short-term electromagnetic precursor is discovered for the disastrous Japan earthquake (EQ) occurred on 11 March 2011. This analysis is based on the records measured by search coil magnetometers located at Nakatsugawa (geographic coordinates; 35.42°N, 137.55°E), Shinojima (34.67°N, 137.01°E), and Izu (34.64°N, 137.01°E) of the Chubu University network. The data of these magnetometers are extensively used to analyze the ULF/ELF seismo-atmospheric radiation. It is then found that the ULF/ELF atmospheric radio emission is reliably detected on 6 March before the main shock on 11 March, probably as a precursory signature of the EQ. Further confirmation on its seismic origin was provided by the observational fact that the azimuths of the radiation source from all observation sites coincide approximately with the region of the forthcoming EQ. Key Points The ULF/ELF electromagnetic radiation before the 2011 3.11 Japanese earthquake ©2013. American Geophysical Union. All Rights Reserved. Source

Solovieva M.,Russian Academy of Sciences | Rozhnoi A.,Russian Academy of Sciences | Fedun V.,University of Sheffield | Schwingenschuh K.,Austrian Academy of Sciences | And 2 more authors.
Annals of Geophysics

Data from the European network of very low/ low frequency (VLF/LF) receivers has been used to study the response of the lower ionosphere to the earthquake of magnitude 5.5 in Vrancea area on November 22, 2014. Negative amplitude anomalies have been observed during 3 days before the earthquake and two days after, on the LF (45.9 kHz) signal passed above the seismic area. No perturbations have been found for the same signal in control paths during this period. Other possible influences both from above and below which can produce perturbations in the ionosphere have been taken into consideration. © 2015 by the Istituto Nazionale di Geofisica e Vulcanologia. All rights reserved. Source

Nickolaenko A.P.,Ukrainian Academy of Sciences | Hayakawa M.,Hayakawa Institute of Seismo Electromagnetics Co. | Hayakawa M.,University of Electro - Communications
Geomatics, Natural Hazards and Risk

The impact of seismogenic ionosphere non-uniformity is considered on the Schumann resonance (SR) signals observed both in the vertical electric and two orthogonal horizontal magnetic field components. The model is able to interpret the anomalous signals observed in Japan in possible association with the earthquakes (EQs) in Taiwan. Changes in the SR intensity arise from a localized reduction of the ionosphere over the EQ epicentre. Signals in the regular Earth-ionosphere cavity are described by using the knee model of vertical conductivity profile. It is suggested that pre-seismic and seismic activity lowers the knee altitude by 20 km at the centre of disturbance, and the perturbation has the Gaussian radial dependence in the 1 Mm zone. The diffraction problem in the cavity with a localized disturbance is resolved by using the Stratton-Chu integral equation. The data of Optical Transient Detector are used to model the source distribution. A pronounced modification is obtained in the intensity around the fourth mode frequency in a form of abrupt spectral changes. The model data are found to be similar to observations, and properties of the model seismic anomalies are discussed. © 2013 Taylor & Francis. Source

Galuk Yu.P.,Saint Petersburg State University | Nickolaenko A.P.,Ukrainian Academy of Sciences | Hayakawa M.,Hayakawa Institute of Seismo Electromagnetics Co.
Telecommunications and Radio Engineering (English translation of Elektrosvyaz and Radiotekhnika)

Investigations remains update of relationship between the parameters of global electromagnetic (Schumann) resonance and characteristics of vertical profile of atmosphere conductivity. We use the rigorous full wave solution of the electrodynamic problem in the spherical Earthionosphere cavity and compare the results with the described in literature heuristic knee model having a single kink. By using parameters of this heuristic model, we constructed vertical profile of atmospheric conductivity and used it in the rigorous full wave solution for the propagation constant of ELF radio waves. Afterwards, the power spectra were computed of vertical electric and horizontal magnetic fields in the framework of the uniform global distribution of the planetary thunderstorm activity. We show that conductivity profile based on the one kink does not match the rigorous full wave solution and the subsequent computations of the power spectra of the Schumann resonance. Source

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