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Author

Andrey Lyakhov

Bio: Andrey Lyakhov is an academic researcher. The author has contributed to research in topics: Ionosphere & Radio propagation. The author has an hindex of 3, co-authored 21 publications receiving 20 citations.

Papers
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Proceedings ArticleDOI
13 Dec 2018
TL;DR: In this paper, the authors analyzed the changes in the parameters of the D region during an X-class flare on September 6, 2017, and showed 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.
Abstract: 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.

6 citations

Proceedings ArticleDOI
13 Dec 2018
TL;DR: In this article, the authors used two widely used empirical models and verified them on the experimental VLF data from Mikhnevo geophysical observatory for 2014 year, and proved the severe limitations of the current empirical models.
Abstract: The empirical models of the lower ionosphere are used for fast prediction of VLF-LF propagation properties, for the initialization in the inverse problem solvers and as a climatological testbed for new numerical models. We used two widely used empirical models and verify them on the experimental VLF data from Mikhnevo geophysical observatory for 2014 year. Numerical results were obtained by parabolic equation method. The presented results prove the severe limitations of the current empirical models. The main bottlenecks are formulated.

5 citations

Proceedings ArticleDOI
13 Dec 2018
TL;DR: In this article, the interrelation and spatio-temporal distribution of geophysical disturbances induced up by the solar flare and their influence on the accuracy of positioning of global navigation satellite systems are shown.
Abstract: 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.

4 citations

Proceedings ArticleDOI
13 Dec 2018
TL;DR: In this article, a probabilistic-statistical model of the D-region of the ionosphere was proposed for the calculation of electron concentration using deterministic-probabilistic modeling.
Abstract: The principles of the probabilistic-statistical modeling of the D–region of the ionosphere are described. The work is devoted to the calculation of electron concentration using deterministic-probabilistic modeling. In this work the electron concentration is calculated using the five-components system of the ionization-recombination cycle equations. Probability density functions (PDFs) of the input parameters of the model are used to solve the system. It was shown that theoretical PDFs of the Ne are in good agreement with two experimental databases of electron concentration. Results of the deterministic-probabilistic model are compared with the experimental VLF signals obtained in geophysical observatory Mikhnevo from the three transmitters in different heliogeophysical conditions.

4 citations

Proceedings ArticleDOI
18 Dec 2019
TL;DR: In this article, the authors used the evidence on VLF-LF propagation under the X-ray solar flares to compare the performance of modern and old ionosphere models on the modern data.
Abstract: The contemporary study of the global change of the atmosphere raise up the problem of models verification, namely, we need the quantified metric to compare models. One of such simple approach is to use the evidence on VLF-LF propagation under the X-ray solar flares. Any flare impacts on the middle atmosphere up to 60 km altitude. Its signature in amplitude record is clear and identifiable. We have a variety of radio paths and any season (or even year of solar cycle) in database. All aforementioned arguments make the strong basis for the model check. The response of the lower ionosphere and middle atmosphere to a solar flare depends on the quality of the source term definition and on the correctness of the chemical processes description. Different approaches are known for the derivation of X-ray excess ionization, varying from classic approach1 to huge Monte Carlo simulations.2 We elaborated the numerical model which is combined from an empirical model of ionization (GOES X-ray measurements) and numerical VLF propagation code.3 It successfully reproduced the first phase of the lower ionosphere response to the extremely strong solar X-flare (X9.9) September 06, 2017. Meanwhile, the decay phase was overestimated. Thus we decided to improve the ionosphere model and compare our model with other popular ionization schemes under the flares of various class. Moreover, all ionospheric models under analysis were realised in two modes: the standard mode with constant chemical rates and in the swarm mode with rates dependence on the altitude and ionization rate. The latter have been received in 70-s from complex kinetic simulations of the high altitude nuclear explosion impact on the ionosphere.4 We expected the improvement of results for intense flares and we wanted to check the quality of contemporary and old ionosphere models on the modern data. The results prove that (a) all models failed under empirical model of ionization; (b) the most promising model is IDG5 in swarm mode; (c) the problem of the minor neutrals is overestimated.

3 citations


Cited by
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Journal ArticleDOI
TL;DR: The role played by the Service of Rapid Magnetic variations (SRMV) is also assessed, followed by a discussion of the main current limiting factors in the process of detection and proposed ways to overcome challenges such as by creating an automatic detection method as discussed by the authors.
Abstract: Solar flare effects (Sfe) are rapid variations in the Earth’s magnetic field and are related to the enhancement of the amount of radiation produced during Solar flare events. They mainly appear in the Earth’s sunlit hemisphere at the same time as the flare observation and have a crochet-like shape. Much progress has been made since Carrington’s first observations in 1859 which are considered to represent the first direct evidence of the connection between the Sun and the Earth’s environment but there is still much to discover. In this paper, we review state-of-the-art developments and the advances made in the knowledge concerning Sfe phenomena while also looking at the challenges that lie ahead. First, we offer a historical approach with a comprehensive description that allows for a better understanding of the main characteristics of Sfe. This frames specific topics like the puzzling reversed-Sfe or the nighttime Sfe. The role played by the Service of Rapid Magnetic variations (SRMV) is also assessed, followed by a discussion of the main current limiting factors in the process of detection and proposed ways to overcome challenges such as by creating an automatic detection method. The paper clarifies some aspects related to the geo-effectiveness of the solar flares producing magnetic disturbances. The importance of the global modelling studies covering critical aspects needed to understand this Sun–Earth system is assessed. Also, we provide an overview of the temporal evolution of the electric currents producing Sfe. The importance of key subjects such as the dynamic aspects of Sfe is developed in another section. Finally, estimations of the size of large flares using ionospheric and magnetic data are reviewed as well as the prospects of these large flare events putting technological systems in danger.

25 citations

Journal ArticleDOI
TL;DR: It is demonstrated that it is required to create probabilistic statistical models of the ionosphere for calculating radio propagation in a wide frequency range and this presents a new type of ionospheric modeling.
Abstract: It is demonstrated that it is required to create probabilistic statistical models of the ionosphere for calculating radio propagation in a wide frequency range. This, in fact, presents a new type of ionospheric modeling. These models are classified into pure statistical and deterministic-stochastic. We describe the key principles of building such models, present some examples of their construction, and discuss some difficulties arising from them.

17 citations

Journal ArticleDOI
TL;DR: In this paper, the results of the reconstruction of the effective height h' and the slope of the profile β of the electron concentration in the D layer of the ionosphere during X-ray flares of M- and X-classes at the midlatitudes were presented.
Abstract: The paper presents the results of the reconstruction of the effective height h' and the slope of the profile β of the electron concentration in the D layer of the ionosphere during X-ray flares of M- and X-classes at the midlatitudes. The reconstruction was carried out with data from measurements at the observatory of the Institute of Geospheres Dynamics of the Russian Academy of Sciences at the Mikhnevo observatory of amplitudes and the phases of signals from VLF transmitters GQD (19.6 kHz) and GBZ (22.1 kHz) that propagate along one mid-latitude path. Based on the calculations, the empirical dependencies of the parameters h' and β on the flare energy according to the X-ray flux measurements on the GOES satellite are in the range 0.05–0.4 nm. Criteria are proposed for the selection of solar flares for the verification of theoretical computational models.

5 citations

Proceedings ArticleDOI
12 Nov 2020
TL;DR: In this article, a verification method of results of lower ionosphere models during solar flares is presented, which is based on radio physical measurements of VLF signals, normalized according to the difference between experimental and theoretical results, obtained during the calm heliogeophysical day, which was followed by the observed solar flares.
Abstract: The paper is devoted to the verification method of results of the lower ionosphere models during solar flares. The verification is based on radio physical measurements of VLF signals. Radio wave amplitude values are normalized according to the difference between experimental and theoretical results, obtained during the calm heliogeophysical day, which is followed by the observed solar flares. This method allows to compare absolute values of radiophysical characteristics without knowing transmitter power. Such an approach makes it possible to evaluate the predictive capabilities of the ionosphere model during flares not only qualitatively, but also quantitatively. As a result of the D-region model verification, it was found that the standard deviation of the difference between experimental and theoretical amplitude of VLF signal is less than 1 dB in ~ 80% of cases

2 citations