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Your search keyword '"Grach, S. M."' showing total 169 results
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169 results on '"Grach, S. M."'

1. Response of ionospheric electron density profile to the action of powerful HF radio-wave radiation

Author

Legostaeva Y. K., Shindin A. V., and Grach S. M.

Subjects
ionosphere, electron heating, powerful hf radiation, ponderomotive expulsion, profile modification, Astrophysics, QB460-466
Abstract

Using electron density and temperature equations, we have modeled the dynamics of the electron density profile in the ionosphere due to the expulsion of plasma from localization regions of plasma waves, pumped by high-power HF radio waves, i.e. wave reflection and upper hybrid resonance regions. Causes of the ionospheric plasma expulsion are an increase in the gas-kinetic pressure due to the ohm heating of electrons by plasma waves, and the high-frequency pressure of plasma waves (ponderomotive expulsion). We have established that the ponderomotive expulsion develops more rapidly and is responsible for the formation of local regions of plasma density depletion near plasma resonances, whereas the gas-kinetic pressure increase is responsible for the formation of lower-density region, which is slower in time and more extended and smoother in height. The results obtained qualitatively agree with the data from the experiment conducted at the HAARP facility in 2014.

Published
2022
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5. Investigation of Joint Effect of Two Mechanisms of Probe Wave Anomalous Attenuation

Author

Zabotin, N. A., Bronin, A. G., Zhbankov, G. A., Komrakov, G. P., and Grach, S. M.

Subjects
Physics - Plasma Physics
Abstract

Two mechanisms of anomalous attenuation of probe waves in the experiments of ionosphere modification are discussed in the paper. The first mechanism is the well-known conversion of ordinary wave into plasma waves due to scattering from random irregularities in the upper-hybrid resonance region. The second mechanism is the multiple scattering. This mechanism is responsible for anomalous attenuation of extraordinary wave have been observed in several experiments. Investigation of joint effect of both mechanisms gives additional possibilities for diagnostics of artificial irregularities., Comment: HTML format

Published
1998

6. Dependence of Ordinary Wave Anomalous Absorption on the sounding Problem Parameters

Author

Bronin, A. G., Grach, S. M., Zhbankov, G. A., and Zabotin, N. A.

Subjects
Physics - Plasma Physics
Abstract

The paper describes the straightforward method of calculation of anomalous absorption of ordinary wave due to transformation into plasma wave in the upper-hybrid resonance region of magnetized plasma with random irregularities. The method is based on the general approach to calculation of scattering or transformation cross-sections in magnetized plasma. The expressions for anomalous attenuation obtained in the paper take into account the thermal motions of the particles and have a wide area of application. Numeric estimations of anomalous absorption for different conditions are carried out., Comment: HTML format, 6 figures

Published
1998

34. Letter to the Editor UHF electromagnetic emission stimulated by HF pumping of the ionosphere

Author

Grach, S. M., Fridman, V. M., Lifshits, L. M., Podstrigach, T. S., Sergeev, E. N., and Snegirev, S. D.

Subjects
Astrophysics::High Energy Astrophysical Phenomena, Physics::Space Physics, Astrophysics::Cosmology and Extragalactic Astrophysics
Abstract

UHF electromagnetic emission (with a frequency near 600 MHz) from the F-region of the ionosphere pumped by an HF powerful radio wave is revealed. Possible mechanisms of the emission excitation, such as plasma mode con-version, scattering or Earth thermal noise emission off the plasma density irregularities, bremsstrahlung and excitation of high Rydberg states of the neutral particles by the accelerated electrons are discussed.Key words. Ionosphere (active experiments; wave-particle interactions) – Solar physics, astrophysics, and astronomy (radio emissions)

Published
2018

35. Properties of the Stimulated Electromagnetic Emissions During the Inclined High‐Frequency Pumping of the Ionosphere Near the Fourth Electron Gyroharmonic at the High‐Frequency Active Auroral Research Program Facility

Author

Shindin, A. V., primary, Grach, S. M., additional, Sergeev, E. N., additional, Smolina, V. P., additional, Pogorelko, N. A., additional, Bernhardt, P. A., additional, Briczinski, S. J., additional, Broughton, M., additional, LaBelle, J., additional, and McCarrick, M. J., additional

Published
2019
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50. Ionospheric plasma density irregularities measured by stimulated electromagnetic emission

Author

Norin, Lars, Grach, S. M., Leyser, Thomas, Thidé, Bo, Sergeev, E. N., Berlin, M., Norin, Lars, Grach, S. M., Leyser, Thomas, Thidé, Bo, Sergeev, E. N., and Berlin, M.

Abstract

It is well known that ionospheric plasma turbulence can be conveniently generated by controlled injection of powerful high-frequency radio beams from the ground. Irradiation of the ionosphere with such radio waves leads to the formation of plasma density structures, striations, and the generation of secondary electromagnetic radiation, a phenomenon known as stimulated electromagnetic emission (SEE). In this paper we present experimental results of the dependence of SEE on decreasing excitation levels of the striations. In the experiments the frequency of the injected radio beam was varied near the fifth harmonic of the local ionospheric electron gyro frequency. We use the SEE measurements to obtain transverse length scales of the striations involved in the generation of the SEE. Our results show that different spectral features of the SEE display different temporal dynamics, suggesting that they are related to striations with different transverse length scales (1 less than or similar to L-perpendicular to less than or similar to 25 m).

Published
2008
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