This paper presents the comprehensive analysis results of the state of the lower and upper ionosphere during an X-class X-ray flare that occurred on June 10, 2014. The method we developed has allowed us to estimate the parameters of the lower ionosphere during a solar flare by the amplitude-phase characteristics of electromagnetic radiation in the VLF range. Comparison of these results with the value of the increment of the total electron content (TEC) obtained from the GNSS receiver located at the Geophysical Observatory «Mikhnevo» showed that the contribution of the D-region (50-80 km) to the change in the TEC value can be 34% at the peak of the X-ray flux.
The research of the space-time dynamics of the Earth's atmosphere and ionosphere disturbances requires complex studies of interrelated processes. The radiophysical complex in the Geophysical Observatory «Mikhnevo», which includes magnetometric, electrophysical, radio-receiving and acoustic equipment and ionospheric sounding instruments, allows us to obtain data on the features of the structure and dynamics of ionospheric plasma in the mid-latitude zone of the European part of the country. Using the complex based on the data of ELF/VLF receivers and GNSS receivers, studies of synchronous variations of the lower and upper ionosphere caused by magnetic storms, solar X-ray flares and experiments on artificial modification of the ionosphere are carried out.
This paper presents a study of the morning terminator impact on the electromagnetic signal amplitudes of VLF stations. The experimental data obtained at the Geophysical Observatory «Mikhnevo» (54.9° N, 37.7° E) in 2015 were used for the analysis. During the passage of the morning terminator, there is a sudden decrease in the signal amplitude. As a result of the study, it was established that this significant change is already observed at 15% of the track illumination.
The work discusses the determination of the radiation-gas-dynamic parameters of a high-speed aluminum plasma jet injected into the ionosphere at an altitude of 140 km using the explosive cumulative generator VGPS-300 used in the "Fluxus" experiments. We describe the algorithm for the calculation of the aforementioned parameters. The results of numerical simulation for the initial stage of the jet plasma dynamics are consistent with the evidence of the gas dynamic and radiation characteristics of the plasma in laboratory experiments and ionospheric experiments "Fluxus" as well.
Disturbances of the Earth's lower ionosphere caused by the precipitation of energetic particles remain one of the priority tasks of geophysics. Changing the parameters of signals from VLF transmitters is the most effective tool for studying ionospheric disturbances. Monitoring the conditions of VLF radio signals propagation at the Geophysical Observatory «Mikhnevo» makes it possible to study disturbances in the D and E regions of the ionosphere. We revealed a significant change in the amplitude of VLF signals from European transmitters and to find their relationship with the dynamics of precipitations recorded by the DMSP satellite during a solar flare in September 2017.
The paper presents the results of an analysis of variations in the effective reflection height h' on the X-ray energy in different spectral ranges during a series of X-ray flares that occurred from September 6 to 10, 1017. It is shown that the effective reflection height h' depends on the X-ray energy in the range up to 0.2 nm. During the period from September 6 to September 10, the parameters of the ionosphere changed significantly - the absorption of X-ray radiation at heights above the D-layer increased.
The study is devoted to the study of atmospheric, electromagnetic and ionospheric effects registered at a distance of about 2000 km from the earthquakes in Greece on May 24, 2014 and November 17, 2015 by the hardware complex of the geophysical observatory "Mikhnevo". One of the mechanisms that provide perturbations of geophysical fields at significant distances from the source is associated with the generation of acoustic waves caused by a surface seismic wave. When acoustic oscillations propagate to the atmosphere and ionosphere, they cause variations in the density of the neutral gas and the electron concentration in the ionosphere. In the D region, this leads to changes in the conductivity and modulation of horizontal ionospheric currents registered on the Earth's surface as variations of the geomagnetic field. The results obtained confirm the possibility of recording acoustic and electromagnetic effects at significant distances from the earthquake center.
The paper presents the results of measurements of the electric field and vertical atmospheric currents in conditions of "fair weather" and their comparison with the Carnegie curve. The features of the measurement data associated with the detection of the evening maximum of the electric field strength are shown.
The paper presents the variations in the parameters of the ionosphere D-layer during x-ray flares of M and X classes on the propagation path of signals from the superluminal waves of the GQD and GBZ transmitters, as well as those adopted by the Mikhnevo State Educational Center. It is shown that, within the framework of the two-parameter Ferguson-White model, the effective reflection height of the VLF signal h’ and the gradient of increase in the electron concentration β at the leading edge of the flare are related to the x-ray energy in the range 0.05–0.4 nm.
This paper presents the perennial results of ionospheric vertical total electron content (TEC) variations using the Global Navigation Satellite System (GNSS) data from the Geophysical Observatory «Michnevo». TEC long data analysis revealed a TEC annual variations and TEC decreasing trend caused by the decline in solar activity during the observation period. Spectral analysis allowed to identify 27 TEC daytime variations, which can be directly related to the period of sun rotation around its axis. Also the TEC distribution from the UV solar radiation flux was made. The linear dependence of the TEC value on the UV flux can be explained by the fact, that UV solar radiation is the main ionization agent of the F region ionosphere.
KEYWORDS: Atmospheric modeling, Solar radiation models, 3D modeling, Solar processes, Physics, Climatology, Satellites, Atmospheric chemistry, Radio propagation
We review the contemporary level of the lower ionosphere study. The progress in ionosphere physics is based on the complex measurements as well as on the self-consistent 3D computer codes but this is not the case for the lower ionosphere. We point out the problems which are necessary for the solar-terrestrial links, transient electrooptical events in the middle atmosphere and even for the global climate community models. Special attention is paid to the problem of verification using satellite and ground-based evidence. The examples from VLF-LF monitoring prove the requirement of further study of the lower ionosphere processes.
KEYWORDS: Receivers, Satellite navigation systems, Satellites, Global Positioning System, Signal processing, Tomography, Data corrections, Spatial resolution, Radio propagation, MATLAB
This paper describes the method of determination of absolute values of TEC according to data of GNSS receivers located in one measuring point. The use of this technique allows obtaining information on the state of the ionosphere in various helio-geophysical facilities. Verification of the results obtained according to the global networks confirmed the correctness of the methodology used.
In September 2017, several X-class solar X-ray flashes occurred. The paper presents the variations of the parameters of the D-layer of the ionosphere during X-ray X-ray flashes on the propagation path of signals from the VLF GQD and GBZ transmitters, and received in the geophysical observatory "Mikhnevo". The dependences of variations in the parameters of the ionosphere from the X-ray flux in different ranges are obtained. It is shown, that the dependences of the parameters of the ionosphere (effective reflection height and electron density increase rate with height) versus the Xray flux in the ranges of 0.05–0.4 nm and 0.1–0.8 nm are very different for different solar X-ray flashes. This may be due both to different initial states of the ionosphere and to the fact that the X-rays radiation with wavelength less than 0.05 nm can play a major role in the ionization of the atmosphere at altitudes of 50-60 km.
Properties of the Schumann resonances have been extensively studied in order to explain their relation with properties of the upper atmosphere and ionosphere. This paper presents the results of an analysis of the frequency variations of the 1st mode of the Schumann resonator in two (North-South and East-West) magnetic field components in the geophysical observatory “Mikhnevo” during solar X-ray flares of M and X classes in 2011–2017. An analysis was made for the influence of the illumination of the signal propagation path and the total electronic content on it on the response magnitude of the variation of the first Schumann resonance frequency. It is shown that the frequency variation of the first mode of the Schumann resonance depends on the helio-geophysical conditions on the signal propagation path, i.e. arc of great circle. It is also shown that the diurnal variation of the sensitivity of the frequency variation of the 1st Schumann resonance to the X-ray flash power correlates well with the diurnal variation of the total electron content of the ionosphere on the signal propagation path. This fact may indicate that the electromagnetic wave at the frequencies of the first Schumann resonance penetrates into the upper ionosphere, namely into the f-layer. And, thus, the characteristics of the F-layer of the ionosphere can affect the parameters of the first Schumann resonance.
The use of global satellite navigation systems for the study of the ionosphere makes it possible to obtain information on ionospheric disturbances and to build maps of the distribution of large-scale ionospheric disturbances. The task of studying small and medium-scale inhomogeneities requires the creation of special methods of measurement and analysis. The system of receivers located at a distance of several hundred meters to 80 km from each other is used in the geophysical Observatory "Mikhnevo" (MIC, 54.9617° N, 37.7626° E) of the Institute of Geosphere dynamics of the Russian Academy of Sciences (http://idg.chph.ras.ru/ru/watch/mikhnevo). The obtained data allow us to estimate the velocity and trajectory of ionospheric inhomogeneity. The development of this approach in methodological terms will clarify the physical mechanisms of transmission of disturbances in the middle latitudes, which should allow to take them into account in the development and improvement of predictive models of ionospheric disturbances.
In the study of the ionosphere total electron content (TEC), defined from the data of global navigation satellite systems, are widely used. It is assumed that the main contribution to the value of TEC is made by the F region. At the same time, the results of many studies show that during the X-ray flares the ionization of the D region can increase substantially, reaching values of 106 cm-3. In this paper, we analyze the changes in the parameters of the D region during an X-class flare on September 6, 2017. It is shown that a correct interpretation of the variations of TEC with powerful X-ray flares requires taking into account of the contribution to its ionization value of the lower ionosphere.
The paper presents the results of an analysis of the frequency variations of the first mode of the of Schumann resonator in the geophysical observatory Mikhnevo of the Institute of Geospheres Dynamics of Russian Academy of Science (IDG RAS) during solar X-ray flares of the M and X classes in 2011 - 2017. It is shown that the frequency variation depends not only on the flash class, but also on the magnetic field component and local time. It is suggested that this is due to the geometry of the path from the African Thunderstorm Activity Center.
The results of the analysis of the navigation task solution in the conditions of registration of the signals of the global navigation satellite systems GPS and GLONASS in the Mikhnevo GFO (the geophysical observatory) are presented. It is shown that in the classical algorithm, the choice of satellites from the observed constellation should be made not according to the criterion of elevation, but by the number of conditionality of the navigation task matrix. The use of adaptive iterative algorithms almost completely compensates geophysical perturbations while maintaining the twofrequency regime.
We study the surface electric field and the vertical atmosphere current at “Mikhnevo” geophysical observatory by means of a sensor cluster. The electric current sensor allows to disambiguate the displacement and conductive currents and to study their variations in sense of geophysical conditions. Data obtained under "fair weather" conditions and under significant perturbations are presented.
Solar flare on September 6, 2017 was one of the strongest in recent years. The powerful X-ray and ultraviolet radiation of the flash caused significant effects in the upper and lower ionosphere, in the geomagnetic field and surface electric field. The interrelation and spatio-temporal distribution of geophysical disturbances induced up by the flare and their influence on the accuracy of positioning of global navigation satellite systems are shown.
The effect of infrasonic pulsed radiation from the Chelyabinsk bolide on the perturbations of the electron concentration in the D region of the Earth's ionosphere is considered. According to the electromagnetic measurements in the geophysical observatory Mikhnevo of the Institute of Geospheres Dynamics of Russian Academy of Science (IDG RAS), an estimate of the displacement of the reflection point of the SDV signals is obtained. Influence of infrasound radiation on the propagation of VLF signals on the Novosibirsk-Mikhnevo path is considered. The amplitude of the displacement of particles of the environment from infrasonic radiation is estimated. There is a good agreement between theoretical and experimental estimates.
KEYWORDS: Solar radiation models, Solar processes, Ionization, Transmitters, Numerical simulations, X-rays, Data modeling, Monte Carlo methods, Physics
The progress in the physics and chemistry of the lower ionosphere depends on the verification of the numerical models on the experimental data. We establish the framework, that the lower ionosphere model can be considered as a valid one, only if the prediction for the VLF-LF radiowave propagation coincides with evidence both in amplitude and phase temporal dynamics. The extremely strong X-flares 06 and 10 September 2017 were chosen as a testbed for the empirical and theoretical models of the midlatitude lower ionosphere. Both models used GOES-15 X-ray flux measurements. Empirical model captures only the time moment of disturbance. Theoretical model captures the main feature in VLF response. We summarize the observed problems in simulation and prospective solutions as well.
We discuss the role and the usage of the ionosphere models in the improvement of UHF-SHF radar operation. The up-to-date empirical ionosphere models (International Reference Ionosphere (IRI), Fully Analytical Ionosphere Model (FAIM), Ne-Quick2) have too crude spatial and temporal resolution. The aforementioned models cannot describe the localized irregularities (like traveling ionospheric disturbances or waves) which, in turn, are regularly observed at the midlatitude high frequency chirp ionosonde. In the presence of such irregularities the additional range error in UHF range can exceed 1-2 km. The poorly known quasi-random nature of such irregularities leads us to the unique solution, namely, the rejecting of the laminar layered ionosphere in favor of the random electron density field. Such new probabilistic ionosphere model must be elaborated and verified on the experimental data.
The report analyzes the optical data received by the MSX satellite during Fluxus and North Star active rocket experiments, conducted in 1997 and 1999 on the injection of high-speed plasma jets into the ionosphere. It has been demonstrated that 1 to1.5 seconds after injection, the irradiation of the background medium increases. The brightness of the luminescence is associated with the bursts of the flow of precipitated electrons, stimulated by injection of a plasma jet.
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