Localized ionospheric disturbance over the earthquake epicentre and modifications of Schumann resonance electromagnetic fields

Abstract

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 Earthionosphere 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.

Scattering of Extremely Low Frequency Electromagnetic Waves by a Localized Seismogenic Ionospheric Perturbation: Observation and Interpretation

“…We will not discuss the specific mechanisms responsible for the changes in the air conductivity, because the detailed information and references might be found in the books by Molchanov and Hayakawa et al (2008) and Ouzounov et al (2018) and in the review paper by Hayakawa and Molchanov (2007), but the mechanism is poorly understood and is currently being studied extensively. The reduction of the lower part of conductivity profile is similar to changes already analyzed by Nickolaenko et al (2006), Hayakawa et al (2008), Nickolaenko and Hayakawa (2013), and Toledo‐Redondo et al (2013). In the present work we use the realistic conductivity profiles, introduce a few types of seismic modifications, and analyze their impact on radio signals in the SR band.…”

“…Still, these reflect both qualitative and quantitative features observed experimentally. These already published data show that seismogenic modifications in the SR spectra might be successfully explained by radio wave reflection from the atmospheric nonuniformity above the EQ position (Galuk et al, 2019; Nickolaenko et al, 2018a, 2018b; Nickolaenko & Hayakawa, 2013; Nickolaenko et al, 2006). The conductivity modifications of this kind are able to influence only ELF radio waves.…”

Disturbances of lower ionosphere above the center of earthquake and anomaly in the global electromagnetic resonance signal. Part 2. Anomalies in the power spectra

“…Для каждой ячейки карты находили геометрические параметры: дистанции от ячейки до наблюдателя и неоднородности, углы прихода α, β S , β R , а также безразмерный параметр M из формулы (12), учитывающий градиенты. Затем с помощью рядов зональных гармоник с ускорен-ной сходимостью [6,12,20] вычислялся вклад ячейки в энергетические спектры компонент поля E, H ЗВ и H ЮС при единичном токовом моменте источника M C (ω) = 1 в однородном резонаторе. В результате получались «единичные» спект-ральные плотности однородной полости Земля-ионосфера.…”

ELF Electromagnetic Waves from Lightning: The Schumann Resonances

“…There are still many open questions in SR research: importance of the day-night variation in the ionosphere conductivity profile [172][173][174]; influence of the latitudinal changes in the Earth magnetic field; polar cap absorption; accuracy of source geolocation; the determination of the spatial lightning distribution from the background records; anomalous SR signals related to earthquakes [175,176]; and impacts of extra-terrestrial disturbances on the Earth-ionosphere cavity. The last topic has received considerable interest over the past few years.…”