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Purpose: Solar eclipses pertain to high-energy sources of disturbance in the subsystems of the Sun–interplanetary-medium–magnetosphere–ionosphere–atmosphere–Earth and the Earth–atmosphere–ionosphere–magnetosphere systems. During the solar eclipse, the coupling between the subsystems in these systems activates, and the parameters of the dynamic processes become disturbed. Investigation of these processes contributes to understanding of the structure and dynamics of the subsystems. The ionospheric response to the solar eclipse depends on the season, local time, magnitude of the solar eclipse, phase of the solar cycle, the observation site, the state of space weather, etc. Therefore, the study of the effects, which each new solar eclipse has on the ionosphere remains an urgent geophysics and radio physics problem. The purpose of this paper is to describe the radio wave characteristics and ionospheric parameters, which accompanied the partial solar eclipse of 10 June 2021 over the City of Kharkiv. Design/methodology/approach: To make observations, the means of the HF Doppler measurements at vertical and oblique incidence available at the V. N. Karazin Kharkiv National University Radiophysical Observatory were employed. The data obtained at the “Lviv” Magnetic Observatory were used for making intercomparison. Findings: The radiophysical observations have been made of the dynamic processes acting in the ionosphere during the solar eclipse of 10 June 2021 and on the reference days. The temporal variations in the Doppler frequency shift observed at vertical and oblique radio paths have been found to be, as a whole, similar. Generally speaking, the Doppler spectra over these radio propagation paths were different. Over the oblique radio paths, the number of rays was greater. The solar eclipse was accompanied by wave activity enhancement in the atmosphere and ionosphere. At least three wave trains were observed. The values of the periods (about 5–12 min) and the relative amplitudes of perturbations in the electron density (δN≈0.3–0.6 %) give evidence that the wave disturbances were caused by atmospheric gravity waves. The amplitude of the 6–8-min period geomagnetic variations has been estimated to be 0.5–1 nT. Approximately the same value has been recorded in the X component of the geomagnetic field at the nearest Magnetic Observatory. The aperiodic effect of the solar eclipse has appeared to be too small (less than 0.01 Hz) to be observed confidently. The smallness of the effect was predetermined by an insignificant magnitude of the partial eclipse over the City of Kharkiv (no more than 0.11). Conclusions: The features of the solar eclipse of 10 June 2021 include an insignificant magnitude of the aperiodic effect and an enhancement in wave activity in the atmosphere and ionosphere. Key words: solar eclipse; ionosphere; Doppler spectrum; Doppler frequency shift; electron density; geomagnetic field; atmospheric gravity wave

On August 4, 2020, a massive explosion rocked the city of Beirut, Lebanon. The explosion yield has been estimated to be equivalent to 1 kt of TNT, and the physical effects of the explosion on the Earth–atmosphere–ionosphere–magnetosphere system have been analyzed in detail. The possible effects of powerful explosions are of considerable interest to geophysicists and radio physicists to analyze. These effects make it possible to reveal the mechanisms for transporting the disturbances in both the vertical and horizontal directions as well as the mechanisms for interaction of the subsystems in the Earth–atmosphere–ionosphere–magnetosphere system. The purpose of the present paper is to describe radio and magnetometer observations of the processes that accompanied the powerful explosion in Beirut on August 4, 2020, in the lower ionosphere and in the geomagnetic field. The observations of the possible response of the near-Earth medium to the explosion have been made with a fluxmeter magnetometer and a radio system for sounding the ionosphere at oblique incidence. The latter system detected an increase of up to 5.3° in the phase of the ionospheric wave and an increase of 3.3% in the signal amplitude caused by an electron density change of approximately 3%. If these increases are due to the explosion, the speed of propagation of the disturbance is estimated to be approximately 3 km/s. The fluxmeter magnetometer has detected changes in the character of variations in the level of the geomagnetic field occurring 5 min and 79 min after the explosion. If these variations were associated with the explosion, the speeds of propagation can be estimated to be tens of km/s and greater as well as 490 m/s. The MHD waves have a greater speed, and the acoustic gravity waves have a smaller speed, respectively.

Purpose: The object of the radio study is to investigate dynamic processes, which occurred over the People’s Republic of China following three moderate (magnitudes 5.9-6.6) earthquakes in Japan in 2018–2019. The distances between the earthquake epicenters and the radio paths midpoints varied from approximately 1300 to 2000 km The aim of the study is to present observations of the dynamic processes in the ionosphere, which accompanied the earthquakes in Japan, and the analysis of intercomparison between the events. Design/methodology/approach: To continuously observe the ionosphere state over the ~ 100-300 -km altitude range, the multi-frequency multiple path radio system for oblique incidence soundings of the ionosphere has been designed by the specialists at the V. N. Karazin National University (Ukraine) and the Harbin Engineering University, PRC (45.78 N, 126.68 E). The basic premise upon which the system operation is based are the measurements of the Doppler shift of frequency, fD, and of the amplitude of radio waves reflected from the ionosphere. The Doppler spectra are calculated over the 20-s intervals, with the Doppler resolution of 0.02 Hz and the time resolution of 7.5 s. Findings: The seismic activity in Japan on July 7, 2018 was accompanied by an increase in a number of rays, by a significant broadening of the Doppler spectra, and by aperiodic processes in the ionosphere at distances no less than 1000–2000 km from the earthquake epicenters. Also, wave disturbances, generated by the seismic waves (speeds of ≈3 km/s), have been revealed in the 4–5-min infrasonic period range; the amplitude, δN, of the quasi-periodic variations in the electron density, N, was observed to be 4.5–9 %, and the duration of the oscillation trains to vary in the 24–55-min range. The relative amplitude δNa, of the electron concentration variations with the period ≈15-30 min caused by the propagation of atmospheric gravity wave (AGW) was estimated to be 30–55 %, the oscillation train duration was observed to be approximately 100 min, and the speed 0.3 km/s. The character of the Doppler spectrum variations, the Doppler shift of frequency over the main ray, and of the signal amplitude were found to be notably different during the September 5, 2018 earthquake and on the reference days. Two characteristic apparent speeds of 3.3 km/s and of ≈500 m/s were revealed. The former is close to that of seismic waves, and the latter to the speed of AGWs in the terrestrial ionosphere. The relative amplitudes in the infrasonic and AGW wave fields were estimated to be δN≈1.5-3 % and δNa≈6-7.5 %, respectively. The April 11, 2019 earthquake was accompanied by the Doppler spectrum broadening by 1-1.5 Hz in the 5–9.8 MHz frequency range, the generation of AGWs with 0.5-1 -km/s speeds and 8-20 -min periods, and by the generation of infrasonic waves with 2-5 -min periods and 0.3-0.4 -km/s speeds. Conclusions: Moderate earthquakes of Richter magnitudes ≈6 have been determined to give rise to dynamic processes in the ionosphere at distances no less than 1000-2000 km. The disturbances are transported by seismic waves with ≈3 km/s speeds and by acoustic and atmospheric gravity waves with 0.3–1 km/s speeds and periods varying from units to tens of minutes. Предмет і мета роботи: Предметом радіофізичного дослідження є динамічні процеси в іоносфері над Китаєм, що слідували за трьома помірними (магнітуда 5.9÷6.6) землетрусами в Японії в 2018–2019 рр. Відстань від епіцентру землетрусу до середини радіотраси змінювалася приблизно від 1300 до 2000 км. Метою роботи є викладення результатів спостереження динамічних процесів в іоносфері, що супроводжували землетруси в Японії, та їх порівняльний аналіз. Методи і методологія: Для безперервного спостереження за станом іоносфери на висотах ~ 100÷300 км використовувався багаточастотний багатотрасовий радіотехнічний комплекс похилого зондування іоносфери, розроблений фахівцями Харківського національного університету імені В. Н. Каразіна (Україна) та Харбінського інженерного університету (КНР, 45.78° пн. ш., 126.68° сх. д.). В основі функціонування комплексу лежать вимірювання значень доплерівського зміщення частоти fD й амплітуд відбитих від іоносфери радіохвиль. Доплерівські спектри обчислюються на інтервалі часу 20 с. Роздільна здатність за частотою становить 0.02 Гц, за часом – 7.5 с. Результати: Сейсмічна активність 7 липня 2018 р. в Японії супроводжувалася аперіодичними процесами в іоносфері на відстанях щонайменш 1÷2 тис. км від епіцентру, посиленням багатомодовості та значним розширенням доплерівських спектрів. Були також виявлені хвильові збурення в діапазоні інфразвукових коливань (період 4÷5 хв) генерованих сейсмічною хвилею (швидкість ≈ 3 км/с). Відносна амплітуда δN квазіперіодичних варіацій концентрації електронів N при цьому становила 4.5÷9 %. Тривалість цугу коливань була в межах 24÷ 55 хв. Відносна амплітуда δNa варіацій концентрації електронів з періодом ≈ 15÷30 хв, викликаних поширенням атмосферної гравітаційної хвилі, становила 30÷55 %. Тривалість хвильового цугу досягала приблизно 100 хв, швидкість – близько 0.3 км/с. Виявлено, що характер варіацій доплерівських спектрів, доплерівського зміщення частоти основної моди й амплітуди сигналу в день землетрусу 5 вересня 2018 р. та в контрольні дні помітно відрізнявся. Виявлено дві характерні удавані швидкості поширення збурень: 3.3 км/с і ≈500 м/с. Перша швидкість близька до швидкості сейсмічних хвиль, а друга – до швидкості атмосферної гравітаційної хвилі в іоносфері Землі. Відносна амплітуда в полі інфразвукової хвилі й атмосферної гравітаційної хвилі була δN ≈1.5÷3 % і δNa≈6÷7.5 % відповідно. Землетрус 11 квітня 2019 р. супроводжувався розширенням доплерівських спектрів на 1÷1.5 Гц в діапазоні частот 5÷9.8 МГц, генерацією атмосферної гравітаційної хвилі зі швидкістю 0.5÷1 км/с і періодом 8÷20 хв, і генерацією інфразвуку з періодом 2÷5 хв та зі швидкістю 0.3÷0.4 км/с. Висновки: Встановлено, що помірні землетруси з магнітудою ≈6 викликають динамічні процеси в іоносфері на відстанях щонайменш 1÷2 тис. км. Переносником збурень є сейсмічні хвилі зі швидкістю ≈3 км/с і акустико-гравітаційні хвилі з періодом від одиниць до десятків хвилин та зі швидкістю 0.3÷1 км/с.

Results obtained from observations of ionospheric disturbances over the People’s Republic of China during the course of the geospace storm of 14 May 2019, one of the largest storms in 2019, are presented. The Harbin Engineering University operates the multi-frequency multipath radio wave diagnostics employing software defined technology and continuously monitoring dynamic process acting in the ionosphere at oblique incidence since April 2018. The basic premise upon which this instrument operation is based is that the digital re-sampling remains coherent with radio frequency for each propagation path, which permits Doppler spectra and signal amplitudes to be calculated along each of the 14 propagation paths. UT dependences of the Doppler spectra, the main mode Doppler shifts of frequency, and signal amplitudes that were measured on the day of the ionospheric storm and on the reference days of 13 and 15 May 2019 have been analyzed. After the magnetic storm onset, the Doppler shift of frequency exhibits an abrupt –1-Hz decrease, indicating the ionospheric storm onset. In addition, quasi-periodic variations in the Doppler shift of frequency, with 5-, 15-, 20-, and 30-min periods and the amplitudes in the range from 0.05 Hz to 0.15 Hz, occur in the course of the storm. These variations are due to modulation by infrasound (5-min period oscillation) and atmospheric gravity waves (15-, 20-, and 30-min period oscillations). In the electron density, the corresponding waves have amplitudes equal to 0.7% and 4–8%, respectively.

The response of the ionosphere to the earthquake of a moderate magnitude (M ≈ 5.9) that occurred in Japan at 11:23:50 UT on 7 July 2018 has been studied using a newly developed coherent multi-frequency radio diagnostic system for remotely probing the ionosphere at oblique incidence. The seismic activity in Japan on 7 July 2018 was accompanied by aperiodic processes in the ionosphere at distances of no less than (1–2) × 103 km from the epicentre, with an enhancement in multiple-mode propagation, and a significant Doppler spectrum broadening. Three ways of transporting disturbances from the earthquake to the changes in the character of Doppler spectra variations have been identified by examination. First, the disturbances are generated by a surface Raleigh wave launched at the earthquake epicentre. They have been ascertained in the infrasonic range (a 3- to 4-min period) of oscillations. The relative amplitude of these quasi-periodic oscillations in the electron density is equal to 1.7–9%. The duration of the oscillation trains is found to be in the range of 24–55 min. The wave disturbance speed of propagation is approximately 3 km/s. Second, wave disturbances have also been ascertained in a 15- to 30-min period range. They could be generated in the vicinity of the epicentre and then propagated as atmospheric gravity waves modulating the electron density in the ionosphere. The relative amplitude of the quasi-periodic disturbances in the electron density is equal to 14 – 34%. The wave train attains a temporal duration of about 100 min and a speed of approximately 0.3 km/s. Third, the broadening of the Doppler spectra toward negative Doppler shifts with the time delay estimated to be 49–124 min, depending on the orientation of the propagation path, is the most pronounced Doppler signature of the disturbances caused by the earthquake. This time delay corresponds to a speed of about 0.3 km/s, and consequently, it suggests that this effect most likely is caused by the atmospheric gravity waves launched at the earthquake epicentre. Apparently, the rearrangement of the ionosphere acts to reverse the sign of the Doppler spectrum shift when the atmospheric gravity waves arrive at the reflection level.

Background. The main cause of geomagnetic disturbances is known to be space sources, processes acting in the solar wind and in the interplanetary medium, as well as falling large celestial bodies. Earthquakes also give rise to geomagnetic effects. In accordance with the systems paradigm, the Earth–atmosphere–ionosphere–magnetosphere system comprises the single system where direct and reverse, positive and negative coupling take place. The mechanism of the earthquake effect on the magnetic field is poorly understood. A rock cracking, a fluctuating movement of fluids in pores, a corona discharge of the high-voltage static charge, etc., are thought to be the processes that give rise to the geomagnetic effect. In the course of earthquakes, seismic, acoustic, atmospheric gravity, and magnetohydrodynamic waves are generated, which provide for coupling between the subsystems in the Earth–atmosphere–ionosphere–magnetosphere system. Purpose of Work. The paper describes the possible response in the level of the geomagnetic field to the earthquake of 26 November 2019 that took place in Albania. Techniques and Methodology. The measurements were taken with the fluxmeter magnetometer at the V. N. Karazin Kharkiv National University Magnetometer Observatory. It delivers 0.5 – 500 pT sensistivity in the 1–1000 s period range over a quite large frequency band of 0.001 to 1 Hz. To study the quasi-periodic processes in detail, the systems spectral analysis of the temporal dependences of the horizontal (H, D) geomagnetic field components has been employed. It includes the short-time Fourier transform, the Fourier transform in a sliding window with a width adjusted to be equal to a fixed number of harmonic periods, and wavelet transform, simultaneously. The wavelet transform employs the Morlet wavelet as a basis function. Results. The quasi-periodic variations in the level of the geomagnetic field observed to appear with a 6 min lag and to last for 70–80 min could be due to the earthquake. These disturbances could be transferred by the magnetohydrodynamic waves. The quasi-periodic variations that were observed to appear with a 97–106 min lag and to last for about 130–140 min were most likely due to the earthquake. They were transferred by the atmospheric gravity waves with a period of 7–14 min. A relative disturbance in the electron density in the atmospheric gravity wave field was observed to be approximately 5.3%. The results obtained from observations of Albanian and Turkish earthquakes show agreement. Conclusions: The magnetic variations in the 1–1000 s period range that were observed to occur before and during the earthquake have been studied.

Purpose:The main cause of geomagnetic disturbances are cosmic sources, processes acting in the solar wind and in the interplanetary medium, as well as large celestial bodies entering the terrestrial atmosphere. Earthquakes (EQs) also act to produce geomagnetic effects. In accordance with the systems paradigm, the Earth–atmosphere–ionosphere–magnetosphere system (EAIMS) constitute a unified system, where positive and negative couplings among the subsystems, as well as feedbacks and precondition among the system components take place. The mechanisms for the action of EQs and processes acting in the lithosphere on the geomagnetic field are poorly understood. It is considered that the EQ action is caused by cracking of rocks, fluctuating motion in the pore fluid, static electricity discharges, etc. In the course of EQs, the seismic, acoustic, atmospheric gravity waves (AGWs), and magnetohydrodynamic (MHD) waves are generated. The purpose of this paper is to describe the magnetic effects of the EQ, which took place in Turkey on 24 January 2020. Design/methodology/approach: The measurements are taken with the fluxmeter magnetometer delivering 0.5-500 pT sensitivity in the 1-1000 s period range, respectively, and in a wide enough studied frequency band within 0.001 to 1 Hz. The EM-II magnetometer with the embedded microcontroller digitizes the magnetometer signals and performs preliminary filtering over 0.5 s time intervals, while the external flash memory is used to store the filtered out magnetometer signals and the times of their acquisition. To investigate quasi-periodic processes in detail, the temporal variations in the level of the H and D components of the geomagnetic field were applied to the systems spectral analysis, which makes use of the short-time Fourier transform, the wavelet transform using the Morlet wavelet as a basis function, and the Fourier transform in a sliding window with a width adjusted to be equal to a fixed number of harmonic periods. Findings: The train of oscillations in the level of the D component observed 25.5 h before the EQ on 23 January 2020 is supposed to be associated with the magnetic precursor. The bidirectional pulse in the H component observed on 24 January 2020 could be due to the piston action of the EQ, which had generated an MHD pulse. The quasi-periodic variations in the level of the H and D components of the geomagnetic field, which followed 75 min after the EQ, were caused by a magnetic disturbance produced by the traveling ionospheric disturbances due to the AGWs launched by the EQ. The magnetic effect amplitude was estimated to be close to 0.3 nT, and the quasi-period to be 700-900 s. The amplitude of the disturbances in the electron density in the AGW field was estimated to be about 8 % and the period of 700-900 s. Damping oscillations in both components of the magnetic field were detected to occur with a period of approximately 120 s. This effect is supposed to be due to the shock wave generated in the atmosphere in the course of the EQ. Conclusions: The magnetic variations associated with the EQ and occurring before and during the EQ have been studied in the 1-1000 s period range. Предмет і мета роботи: Головною причиною геомагнітних збурень є космічні джерела, процеси в сонячному вітрі та в міжпланетному середовищі, падіння великих космічних тіл. До геомагнітного ефекту призводять також землетруси. Згідно системної парадигми об’єкт Земля – атмосфера – іоносфера – магнітосфера є єдиною системою, де мають місце прямі та зворотні, позитивні та негативні зв’язки. Механізм впливу літосферних процесів і землетрусів на магнітне поле вивчений недостатньо. Вважається, що до цього впливу призводять розтріскування порід, флуктуюючий рух у поровій рідині, розряди статичної електрики тощо. Під час землетрусу генеруються сейсмічні, акустико-гравітаційні хвилі (АГХ) та магнітогідродинамічні (МГД) хвилі. Мета цієї роботи – опис магнітного ефекту землетруса, який мав місце 24 січня 2020 р. в Туреччині. Методи та методологія: Вимірювання виконані за допомогою магнітометра-флюксметра. Він має високу чутливість (0.5÷500 пТл у діапазоні періодів коливань рівня геомагнітного поля 1÷1000 с відповідно) і досить широку смугу досліджуваних частот (від 0.001 до 1 Гц). Магнітометр ІМ-II підключений до спеціалізованого мікроконтролерного реєстратора, який виконує поцифрування та попередню фільтрацію магнітометричних сигналів на інтервалах 0.5 с, а також зберігає відфільтровані відліки і час їх отримання в USB флеш-пам’яті. Для детального дослідження квазіперіодичних процесів використовувався системний спектральний аналіз часових варіацій рівня H і D компонент геомагнітного поля. Він ґрунтується на одночасному застосуванні віконного перетворення Фур’є, адаптивного перетворення Фур’є та вейвлет-перетворення. В останньому використовувався материнський вейвлет у вигляді функції Морлє. Результати: Припускається, що спостережуваний 23 січня 2020 р. приблизно за 25.5 год до землетрусу цуг коливань у рівні D-компоненти міг бути пов’язаний з магнітним передвісником. Двохполярний імпульс в H-компоненті 24 січня 2020 р. міг бути зумовлений поршневою дією землетрусу, який згенерував МГД імпульс. Квазіперіодичні варіації рівня H і D компонент геомагнітного поля, що спостерігалися через 75 хв після землетрусу, були викликані генерацією магнітного збурення рухомими іоносферними збуреннями, зумовленими АГХ від землетрусу. Амплітуда магнітного ефекту була близька до 0.3 нТл, квазіперіод – до 700÷900 с. За оцінками відносна амплітуда збурень концентрації електронів у полі АГХ становила близько 8 %, а період – 700÷900 с. Виявлено затухаючі коливання в обох компонентах магнітного поля з періодом близько 120 с. Припускається, що цей ефект пов’язаний з генерацією ударної хвилі в атмосфері протягом землетрусу. Висновок: Вивчено магнітні варіації в діапазоні періодів 1÷1000 с, що супроводжували підготовку землетрусу і саму сейсмічну подію.

The results of observations of quasi-periodic variations of horizontal components of the geomagnetic field, the Doppler frequency shift of the radio waves reflected from the ionosphere, and observations of anomalous traces in ionograms during a catastrophe at the largest European ammunition depot on March 23, 2017, are presented. It is shown that the catastrophe was accompanied by oscillations of the geomagnetic field level (with periods from 5–6 to 13–14 min and an amplitude of 2–3 nT) and the ionospheric electron density (with periods from 14–16 to 50–60 min and a relative amplitude of ∼1–10%). A mechanism for the transfer of disturbances from the catastrophe site to the ionosphere altitudes is proposed. A key role in this mechanism is played by the acoustic gravity waves generated by widespread explosions and large-scale fire events.

The results of observations of disturbances in the lower and middle ionosphere and in the geomagnetic field accompanying the partial solar eclipse over Kharkov are presented. The ionospheric effects have been studied with the use of an ionosonde and measurements of the phase and amplitude of a radio signal with a frequency of 66.(6) kHz on the Moscow–Kharkov route, and the effects in the magnetic field have been analyzed with the help of a magnetometer–fluxmeter in the range of periods from 1 to 1000 s. Disturbances in both the lower and middle ionosphere, as well as in the geomagnetic field, have been detected. The observation results have been compared with the results of a simulation of physical processes accompanying the solar eclipse. A good agreement has been found between observational and modeling results.

A multi-path multi-frequency passive HF Doppler radar for oblique-incidence sounding the ionosphere, that has been produced in collaboration between researchers at the Harbin Engineering University and V. N. Karazin Kharkiv National University, is briefly described. An original software package has been designed, and the implemented autoregressive spectrum analysis gives a root-mean-square Doppler line error of 0.02 Hz and 7.5-s time resolution. The radar has been tested over the course of several months in an ionospheric dynamical process monitoring mode.

Urgency. There is an urgent need to study the interactions in the Earth – atmosphere – ionosphere – magnetosphere system. To identify direct and reverse, positive and negative links among the subsystems, sources producing massive releases of energy are commonly used. In this paper, the Chuysk earthquakes whose Richter magnitudes vary from 4.5 to 7.3 are considered as such a source. The aim of this paper is to present the findings of studying a possible response of the geomagnetic field in the 1 – 1000-s period variations to the preparation and occurrence of the Chuysk earthquakes of September – October 2003. Techniques and Methodology. The measurements were carried out using the fluxgate magnetometer located at the V. N. Karazin Kharkiv National University Geomagnetic Observatory. The sensitivity of the magnetometer is 0.5 – 500 pT in the 1 – 1000-s period range. The data processing was performed in three stages. First, the signals from the magnetometer, recorded in relative magnetometer units, were converted into absolute units, taking into account the magnetometer frequency response. Second, band-pass filtering was performed in the 1 – 10-s, 10 – 100-s, and 100 – 1000-s period ranges. Third, a system spectral analysis of time variations in the H- and D-components of the geomagnetic field was undertaken. Results: Forty three minutes and one-hundred-sixty-three minutes prior to the earthquake of Richter magnitude 7.3, quasi-periodic variations of the geomagnetic field were observed. These variations may be an earthquake magnetic precursor, and the mechanism of such a precursor has been described. After the earthquakes of Richter magnitudes 7.3, 6.7, and 7.0, quasi-periodic variations of the geomagnetic field were detected. Such variations may be caused by the perturbation transfer due to seismic waves with speeds in the 1.9 – 5.3-km/s range and owing to atmospheric gravity waves traveling with speeds in the 320- to 670-m/s range. On October 1, 2003, the changes in the character of the variations occurred with time delays of 0 to 5 min. If these variations were associated with earthquakes, the magnetohydrodynamic waves could act as an agent that transferred the disturbances. Conclusions: The moderate earthquakes are determined to be able to cause geomagnetic field disturbances recordable at distances of about 3,500 km from the epicenter.

This paper presents the results of radio observations of ionospheric disturbances associated with the fall of a meteoroid (unique in its initial energy of 173 kt TNT equivalent) off the east coast of the Kamchatka Peninsula on 18 December 2018. The ionospheric disturbances were measured with the multipath radio system designed for oblique sounding and located at the Harbin Engineering University campus, the People's Republic of China (PRC). The main results are as follows. The ionospheric disturbances following the Kamchatka meteoroid entry and explosion have been detected in the temporal variations in the Doppler spectra and signal amplitudes observed over six oblique propagation paths. The possible disturbances have 2–3 groups of time delays. Depending on the distance between the terminal detonation point and the propagation path midpoint, these time delays fall into the 24–43-min, 93–136-min and 141–183-min time intervals, corresponding to the apparent speeds of 1.9–2.9 km/s, 620–770 m/s and 310–500 m/s, respectively. The disturbances with the apparent speeds of hundreds of meters per second and periods of about 10–15 min are transported by atmospheric gravity waves. The disturbances propagating with the 1.9–2.9-km/s apparent speeds could be caused by ionospheric processes due to the seismic waves generated by the meteoroid explosion.

The MF radar developed for remotely probing the near-Earth space environment and the technique for diagnosing plasma parameters in the electrically active mesosphere have enabled the determination of the basic electrodynamic characteristics of this region, which are required for achieving the fundamental physical understanding and can be used in practical applications (Sun-Earth connections, modeling the ionosphere as well as natural and anthropogenic global disturbances, near-Earth environment monitoring, earthquake predictions, and radio propagation forecasting). In particular, the average daily electric fields intrinsic to the mesosphere have been determined for the first time.

The results of the experimental investigations of variations in ionospheric radio signal and radio noise characteristics over 3 kHz-30 MHz, caused by effects of sources of energy yield of different physical nature are presented.