The propagation of ELF-ULF electromagnetic waves in the Earth-ionosphere waveguide is the subject of a long-term study at the Sadovsky Institute of geospheres dynamics within the geophysical vertical framework. This study closes the chain of processes that start from the solar activity and occur in the upper geospheres with the problems of the lithosphere-ionosphere interaction. The 3D numerical model is described with results of verification on the analytical solutions and applications to a number of lower ionosphere models. In conclusion we set up the list of the forthcoming problems in SR physics which are most important for the physics and chemistry of environment under the global climate change.
The current paper contains a description of a new postprocessing methodology for Schumann Resonance data, which provides resonance characteristics in terms of probability density function. This new approach has been applied for Mikhnevo observatory SR data during 2016{2020 to yield seasonal variations of resonance characteristics.
The talk presents new results on the verification of the global atmosphere-ionosphere model WACCM-X using radiophysical data from the "Mikhnevo" midlatitude geophysical observatory (IDG RAS). VLF stations records and Schumann resonances evidence were used. The model failed in reproducing VLF amplitudes and phases temporal dynamics. The magnitudes of Schumann resonances are overestimated (1-3 Hz). The performance of the global model is insufficient and further elaboration is required.
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.
The work is devoted to an effective method of radiation transfer equations (multi-group diffusion equations) solving used in the numerical simulations of strong perturbations in the atmosphere. The finite-difference approximations of these equations based on the conservative properties of finite difference schemes are presented. In this scheme the analytical solutions of diffusion equations (both for the energy density and for the flux density) are determined inside each layer of a difference grid under the assumption of constancy of the gas-dynamic parameters. The results of test calculations of a number of problems are presented.
Verification of the lower ionosphere models on VLF evidence requires robust radio wave propagation code. It, in turn, must handle inhomogeneous, disperse, anisotropic medium. We present results for FDTD, FVFD and complete mode sum methods for homogeneous and inhomogeneous model ionospheres. The quantitative results are presented on required memory, achievable precision and stability. The fastest, easiest and most suitable for ionosphere model verification problem method is FVFD. FDTD is general but it requires supercomputer resources in the problem of the lower ionosphere model verification.
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.
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.
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