On a model of artificial F-spread in the ionosphere

The results of a complex experiment on the synchronous observation of geostationary-satellite signals and of reflected HF signals of the vertical-sounding station in the course of ionosphere modification by powerful short waves are analyzed using the method of refractive scattering of radio waves. We show that the main statements of the known stochastic theory of F-spread in the ionosphere can be used in the development of a model of artificial F-spread. In particular, the artificial F-spread can be described as multiple-ray propagation of short radio waves in the ionosphere modified by high-power radio waves, the electron-density distribution of which is a random process locally stationary in space and time.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 39, No. 7, pp. 876–881, July, 1996.This paper was supported by the Russian Foundation for Fundamental Research (project 95-02-03716).     

Artificial periodic irregularities,hydrodynamic instabilities,and dynamic processes in the mesosphere—lower thermosphere

We present the results of measuring characteristics of the ionosphere and neutral atmosphere by the method of resonant scattering of radio waves by artificial periodic irregularities of the ionospheric plasma in the altitude range 90–120 km. It is shown that the altitude–time variations of the measured characteristics are in many respects stipulated by the propagation of atmospheric waves. Hydrodynamic instabilities in the mesosphere—lower thermosphere are analyzed. Criteria of development of different-type instabilities are presented. Contribution of different processes to the dynamics of the medium is estimated on the basis of the measurement results.     

Radar observations of artificial ionospheric turbulence during a magnetic storm

We present the results of radar observations of artificial ionospheric turbulence (AIT) created due to modification of the ionosphere by high-power radio emission from the Sura heating facility (Nizhny Novgorod region, Russia). Measurements were carried out in August 18–22, 2003 in the evening time (16:00–20:00 UT) with the use of over-the-horizon chirp HF radars on the Khabarovsk-Rostov-on-Don, Irkutsk-Rostov-on-Don, Inskip (England)-Rostov-on-Don paths, and also on the Moscow-Rostov-on-Don path for which reference signals of the standard-time RVM station were received. It is found that conditions for propagation of HF signals through the upper ionosphere at frequencies exceeding the maximum usable frequency for standard hop propagation through the F region were realized on the Irkutsk-Sura path in the presence of the powerful sporadic E_s layer. The presence of such signals was revealed at the Rostov-on-Don station by receiving radio waves which escape from the altitudes of the ionospheric F region due to scattering by artificial small-scale magnetic-field-aligned irregularities. We studied the ionospheric effects of a magnetic storm occurring during the experiment by using the measurement data of the Doppler frequency shift of signals scattered by artificial ionospheric turbulence. It is shown that during a magnetic storm, the electric field and the drift velocity of irregularities at the altitudes of the F layer over the Sura facility reach values of 8.6 mV/m and 186 m/s, respectively, which are typical of the high-latitude ionosphere. We consider the relation between quasi-periodic oscillations of the Doppler frequency shift of the scattered signal and propagation of magnetohydrodynamic waves excited during the magnetospheric storm.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 47, No. 9, pp. 722–738, September, 2004.     

Artificial periodic irregularities,wave phenomena in the lower ionosphere,and the sporadic <Emphasis Type="Italic">E</Emphasis> layer

We present new results of studying the artificial periodic irregularities produced in the ionosphere by the radio emission of the high-power heating facility “Sura” during the period of observations of the sporadic E layer. Basing on the measurement results for the velocity of the vertical plasma motion and the electron profile density in the E region of the ionosphere, which were obtained by the method of resonance scattering of radiowaves by an artificially produced periodic structure, we analyze the possibility to produce a sporadic E layer by driving metal ions affected by the vertical shear of the velocity, which occurs at these altitudes due to the propagation of internal gravity waves. The parameters of these waves are evaluated, as well as the mass and concentration of metal ions in the sporadic E layer.     

On thermomagnetic instability during ionospheric modification by powerful radio waves

The possibility of excitation of thermomagnetic instability in the ionospheric F-region with an external DC electric field on exposure to waves from powerful ground-based radio transmissions is discussed. The threshold and growth rate of the instability are determined. It is shown that such instability can appear in local regions with a rather high level of plasma waves and in the high-latitude ionosphere, especially for high ionospheric-plasma drift velocities.Scientific-Research Institute of Radiophysics. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 37, No. 5, pp. 674–679, May, 1994.     

Model of interaction between decameter-decimenter radio waves and a strongly inhomogeneous mid-latitude ionosphere

A model of decameter-decimeter radio wave propagation in a strongly inhomogeneous mid-latitude ionosphere is constructed using a modified method of radio wave refractive scattering. The model establishes the relationship between the basic statistical radio wave characteristics and the turbulence parameters of the upper ionosphere. Different aspects of the theory of radio wave refractive scattering are considered in application to the study of amplitude and phase fluctuations of decameter-decimeter radio waves propagating in a three-dimensional randomly inhomogeneous ionosphere with an arbitrary electron density distribution. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 11, pp. 1323–1341, November, 1997.     

Field-aligned scattering of HF radio waves under conditions of action of high-power oblique radio waves on the ionosphere

We present the results of experimental studies of the features of field-aligned scattering of HF radio waves for different angles of incidence of high-power radio waves on the ionosphere. The amplitude, Doppler frequency shift, and azimuthal and vertical arrival angles of the scattered signals are measured. Calculated ray paths in the magnetoactive ionosphere are compared with experimental data on the scattered-signal reception under conditions of action of high-power oblique radio waves on the ionosphere. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 8, pp. 669–677, August 2007.     

The wideband attenuation of short radio waves on mid-latitude paths during X-ray flares in January 2005

We present the results of the ionosphere oblique chirp sounding on the Cyprus—Nizhny Novgorod, Cyprus—Rostov-on-Don, and Moscow—Rostov-on-Don mid-latitude paths during X-ray flares in January 17, 19, and 20, 2005. It is found that during strong flares the blackout of short radio waves was observed over the entire frequency range of chirp sounding on the Cyprus—Nizhny Novgorod and Cyprus—Rostov-on-Don paths. Modeling of the electron-density profiles in the lower ionosphere based on absorption of short radio waves on the Moscow—Rostov-on-Don path at different stages of the decay of the X-ray radiation intensity is carried out. It is shown that at the instant corresponding to the maximum value of the flare radiation flux, the electron density in the lower ionosphere at altitudes 60–80 km increased by a factor of about 10 and 100 for flares with radiation flux densities 5·10⁻² and 3·10⁻¹ erg/(cm ²·s) in the wavelength range 0.5–4.0 Å which took place in January 19 and 20, respectively. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 1, pp. 1–8, January 2007.     

Influence of ionospheric irregularities on the form of radio signal scattering spectrum in over-the-horizon radar sounding of the rough sea surface

Abstract

This paper is concerned with the backscattering of HF radio waves from the rough sea surface, which have propagated through the ionosphere with random large-scale irregularities.

For the sake of simplicity, it is assumed in calculations that the rough sea surface is a perfectly conducting surface with the known Philips power spectrum of irregularities. Ionospheric irregularities of a random medium that are isotropic and single-scale ones, with a Gaussian spectrum, are considered within the limits of the hypothesis of frozen-in irregularities.

Within the first approximation of perturbation theory, using, as the incident wave and the Green function, their geometrical-optics approximations, we obtained the expression for the backscattering spectrum of the ionospheric chirp radio signal with a Gaussian envelope. The expression involves the parameters of the receive–transmit antenna, the signal, the propagation medium, and of the scattering surface. Numerical simulation was used to investigate the influence of all the above-mentioned parameters on the backscattering spectrum. It is shown that travel of ionospheric irregularities has the largest influence on the scattering spectrum, the signal parameters mainly determine the size of the scattering area in the range, and the form of the coherent integration window determines the form of the received signal and can distort it.     

Multipower spectrum of small-scale ionospheric turbulence

We consider the problem of diagnostics of the local structure of small-scale ionospheric turbulence using the multifractal analysis of received signals from the Earth’s orbital satellites after the radio sounding of the inhomogeneous ionosphere by these signals. In particular, it is shown that analysis of the multifractal structure of the received-signal amplitude records by the method of multidimensional structural functions allows one to determine the indices of the multipower local spectra of the small-scale ionospheric turbulence, which are inherent in it due to the nonuniform spatial distribution of small-scale fluctuations of the electron number density. It is noted that information on the multipower spectrum of small-scale ionospheric turbulence is not available for the conventional radio scintillation method based on the classical spectral analysis of received signals during the remote radio sounding of the ionosphere. At the same time, the method of multidimensional structural functions is efficient under conditions of actual nonstationarity of the process of scattering of the HF radio waves by the randomly inhomogeneous ionospheric plasma. The method of multidimensional structural functions is used for the multifractal processing of received signals of orbital satellites during special experiments on radio sounding of the midlatitude ionosphere under natural conditions and its modification by high-power HF radio waves. First data on the indices of the multipower local spectra of small-scale ionospheric turbulence are obtained. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 52, No. 1, pp. 14–22, January 2009.     

Sounding of an artificially perturbed ionosphere by means of an ionosonde/position finder with chirp modulation of the signal

We describe the operation of an ionosonde/position finder with chirp modulation of the signal. The first results of measuring the characteristics of short-wave radio signals scattered by artificial small-scale inhomogeneities, which were obtained by means of an ionosonde/position finder on the IZMIRAN—“SURA”—Rostov-on-Don path are presented. It was found that under certain ionospheric conditions, the angular and frequency selection of the scattered signals take place, in which case the signals are observed simultaneously in several frequency intervals (mainly, in three, namely, 6–9.5 MHz, 10–12 MHz, and 15–18 MHz) with different angles of incidence of radio waves in the vertical plane. In this case, the incidence angles were 20◦–35◦, 18◦–32◦, and 10◦–20◦ from the horizon for the first, second, and third frequency interval, respectively. Ionograms of oblique sounding were modeled allowing for the scattering of radio waves by artificial small-scale inhomogeneities. It is shown that at frequencies from 10 to 12 MHz, aspect conditions are fulfilled for the signals ducting along the high-angle beam (Pedersen mode). At frequencies 15–18 MHz (higher than the maximum observable frequency of the forward signal on the path IZMIRAN—Rostov-on-Don), aspect scattering conditions are fulfilled for the signals incident on a scattering area in the ascending part of the trajectory. At low frequencies 6–9.5 MHz (below the maximum observed frequency of the forward signal on the IZMIRAN—Rostov-on-Don path), the observable additional signals are caused by the scattering of radio waves by artificial inhomogeneities with subsequent relfection of the scattered signal from the Earth on the “SURA”—Rostov-on-Don path. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 52, No. 4, pp. 267–278, April 2009.     

Results of studying the sporadic <Emphasis Type="Italic">E</Emphasis> layer by the method of resonant scattering of radio waves by artificial periodic inhomogeneities of the ionospheric plasma

We report on the results of studying the lower ionosphere by a method based on the resonant scattering of radio waves by artificial periodic inhomogeneities of the ionospheric plasma. Different aspects of studying the sporadic E layer such as the influence of the vertical transfer on its formation, the possibility of examination of its ion composition, and the influence of the ionosphere heating on the layer characteristics are discussed. The results of determining the parameters of the E _s layer and some characteristics of the lower ionosphere during the creation of artificial periodic inhomogeneities at two frequencies are presented. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 11, pp. 956–969, November 2008.     

Influence of ionospheric irregularities on the form of radio signal scattering spectrum in over-the-horizon radar sounding of the rough sea surface

This paper is concerned with the backscattering of HF radio waves from the rough sea surface, which have propagated through the ionosphere with random large-scale irregularities.

For the sake of simplicity, it is assumed in calculations that the rough sea surface is a perfectly conducting surface with the known Philips power spectrum of irregularities. Ionospheric irregularities of a random medium that are isotropic and single-scale ones, with a Gaussian spectrum, are considered within the limits of the hypothesis of frozen-in irregularities.

Within the first approximation of perturbation theory, using, as the incident wave and the Green function, their geometrical-optics approximations, we obtained the expression for the backscattering spectrum of the ionospheric chirp radio signal with a Gaussian envelope. The expression involves the parameters of the receive-transmit antenna, the signal, the propagation medium, and of the scattering surface. Numerical simulation was used to investigate the influence of all the above-mentioned parameters on the backscattering spectrum. It is shown that travel of ionospheric irregularities has the largest influence on the scattering spectrum, the signal parameters mainly determine the size of the scattering area in the range, and the form of the coherent integration window determines the form of the received signal and can distort it.     

Uniform integral representation for the fluctuating field propagating through the multi-scale media

A uniform integral representation for the wave field propagating through the statistically homogeneous multi-scale medium was obtained. It is shown that the considered expression for the field contains the limiting cases for both the Born’s approximation for the single-scattered field and a phase approximation of geometric optics method. Hybrid method formulae for calculation of the fluctuation field, taking into account the effect of backscattering enhancement can be obtained from the investigated integral representation, provided that the spectrum of inhomogeneities can be represented as a sum of two uncorrelated components: small-scale and large-scale. The paper contains the numerical simulation results of the effect of average intensity enhancement of the backscattered field in the medium containing both large- and small-scale irregularities. Unlike the hybrid method of calculation, the proposed approach does not require explicit separation of the inhomogeneities spectrum into two uncorrelated components and allows investigating the effect of the average intensity enhancement of the backscattered field in a more general situation. In particular, numerical calculations have shown that the effect of enhancement of the backscattered signal may occur in the study of the high-latitude ionosphere by method of incoherent scattering of radio waves.     

Preliminary results of the ultralong-range sounding of ionospheric irregularities using the ducted mode

We present preliminary experimental results concerning transequatorial propagation (TEP) of HF waves upon chirp sounding over the 11950-km path alice Springs (Australia)-Yoshkar-Ola (Russia). The measurements were made in August, 1998. Two anomalous signals with delays of 3.0 and 4.5 ms with respect to the main mode were observed during night time (21:30–23:00 UT). The maximum observed frequencies (MOF) of these signals were 2–3 MHz greater than the main-mode MOF. Simulations allowed us to identify these signals as the ducted signals trapped in theFE interlayer duct due to radiowave refraction on a negative gradient of the electron density and that escaped from the duct due to the scattering by small-scale field-aligned irregularities of the subpolar ionosphere. We discuss radiophysical and geophysical aspects concerning localization of the irregularities responsible for scattering and perspectives of using the ducted mode for over-the-horizon diagnostics of the inhomogeneous structure of the ionosphere with a global network of chirp sounders and HF radars. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 12, pp. 1136–1142, December 1999.     

Poynting flux impulses and the ionospheric switching of geomagnetic substorms

Observations were made of impulse events in Poynting flux calculated from electric and magnetic disturbances encountered by the Polar satellite when on high-latitude field-lines in the magnetotail. These were found to be coincident within±6 min with impulsive spikes in cosmic radio background absorption in the D region of the ionosphere as detected by the Imaging Riometer for Ionospheric Studies riometer in Finland. They were also coincident with substorm onset at the same geomagnetic latitude as determined by a change of gradient in International Monitor for Auroral Geomagnetic Effects’ X-component magnetograms. The interpretation of the observations was that magnetospheric compression waves from the geomagnetic equator region of the magnetotail were coupling to progressively initiate field-guided Alfvén shear waves towards higher geomagnetic latitudes over a large volume of the magnetosphere. The study suggested that they were then able either directly or indirectly to ionise the D region of the ionosphere and in the process to cut deep electrically conducting channels between the magnetosphere and the ionosphere through which currents could flow and initiate the characteristic signature of geomagnetic substorms in ground magnetograms.     

Vertical Velocities and Temperature of the Neutral Component in the Upper Atmosphere

Results of measurements of the velocity of the vertical plasma motion and the temperature of the neutral component in the upper atmosphere and comparison of variations in these parameters have been described. The measurements have been carried out by the resonance scattering of radio waves by artificial periodic irregularities in the ionospheric plasma. The irregularities arise when the ionosphere is modificated by a powerful high-frequency radio emission from a Sura midlatitude heating facility. Comparison has been conducted using experimental data on altitude- and time-dependent variations in the above parameters obtained in experiments of 2010 and 2014. It has been shown that, above 100 km, wavelike variations in temperature and velocity are commonly observed simultaneously. In the absence of wavelike variations, there is a tendency to an increase in temperature with an increase in the velocity of the vertical plasma motion regardless of direction. This tendency can be attributed to thermal flows directed upward from the turbulent region of the ionosphere.     

Radiophysical and radio astronomical diagnostics of ionospheric effects induced by a ground-based infrasonic transmitter (preliminary results)

We present results of preliminary studies aimed at detection of weak ionospheric disturbances induced by acoustic emission of a ground-based controlled transmitter. Radio astronomical and radiophysical facilities based on the decameter radio telescope URAN-3 were used in these experiments. Three methods were applied in this study: occultation of the disturbed region by radio emission from discrete cosmic sources, scattering of sounding radio waves from the perturbed ionospheric region, and weakly-oblique sounding of the ionosphere. It is shown that the parameters of transmitted, scattered, and reflected signals are well correlated with the parameters of the acoustic radiation, and that the weak ionospheric disturbances detected in our experiments are actually induced by the acoustic radiation. G. V. Karpenko Physico-Mechanical Institute of the National Academy of Sciences of Ukraine, Khar'kov, Ukraine. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 8, pp. 785–798, August 1999.     

Spectra of Stimulated Electromagnetic Emission of the Ionosphere Sweeping of the Pump Wave Frequency Near Gyroharmonics. II. Discussion of the Results

Alternative mechanisms of generation of the stimulated electromagnetic emission (SEE) excited in the ionosphere by high-power radio waves are analyzed on the basis of measurements of the SEE spectra obtained during the pump-wave frequency sweeping near the forth (n = 4) and fifth (n = 5) harmonics of the electron gyrofrequency nf_ce [1] and their comparison with the existing physical models. A method for determination of the magnetic field strength and plasma density near the double-resonance region in the ionosphere is developed. It is shown that the generation of the broad upshifted maximum (BUM) feature in the SEE spectrum should occur several kilometers below the double-resonance altitude. A role of high-frequency plasma modes and small-scale magnetic field-aligned irregularities, excited under ionosphere pumping by a high-power radio wave, in the formation of SEE spectra is demonstrated. It is shown that the difference in the emission intensities for f₀ ≲ nf_ce and f₀ > nf_ce is related to different regions (altitudes) at which the plasma waves exist in these cases. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 7, pp. 553–570, July 2008.     

Magnetic zenith effect and some features of the multifractal structure of the small-scale artificial ionospheric turbulence

We present the results of the experiment on studying the multifractal structure (with inhomogeneity sizes from tens to hundreds of meters across the Earth’s magnetic field) of the artificial ionospheric turbulence when the midlatitude ionosphere is affected by high-power HF radio waves. The experimental studies were performed on the basis of the “Sura” heating facility with the help of radio sounding of the disturbed region of the ionospheric plasma by signals from the Earth’s orbital satellites. The influence of the magnetic zenith effect on measured multifractal characteristics of the small-scale artificial turbulence of the midlatitude ionosphere was examined. In the case of vertical radio sounding of the disturbed ionosphere region, the measured multipower and generalized multifractal spectra of turbulence coincide well with similar multifractal characteristics of the ionospheric turbulence under natural conditions. This result is explained by the fact that the scattering of signals by weak quasi-isotropic small-scale inhomogeneities of the electron number density in a thick layer with a typical size of several hundred kilometers above the region of reflection of high-power HF radio waves gives the major contribution to the observed amplitude fluctuations of received signals. In the case of oblique sounding of the disturbance region at small angles between the line of sight to the satellite and the direction of the Earth’s magnetic field, the nonuniform structure of the small-scale turbulence with a relatively narrow multipower spectrum and small variations in the generalized multifractal spectrum of the electron number density was detected. Such a fairly well ordered structure of the turbulence is explained by the influence of the magnetic zenith effect on the generation of anisotropic small-scale artificial turbulence in a thin layer having a typical size of several ten kilometers and located below the pump-wave reflection height in the upper ionosphere.