Investigation of wave motions in the lower ionosphere by the method of resonance scattering of radio waves from artificial periodic inhomogeneities

We present the results of studies of wave motions at lower-ionosphere altitudes by a new method based on measurements of the velocity of vertical motion of plasma by the variation of the phase of the signal that is backscattered from artificial periodic inhomogeneities of electron density (ionospheric arrays). The method allows us to study processes with different time scales and periods of from several dozens of seconds to some hours or longer. In the course of long-term 1990–1991 observations conducted near Nizhny Novgorod we determined some dynamic and spectral characteristics of internal gravity waves. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 3, pp. 308–321, March, 1997.     

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.     

Analysis of appearance of moving ionospheric disturbances of the “sickle” type at middle latitudes

We present the results of analysis of the data of vertical ionospheric sounding at the Zimenki test site (Nizhny Novgorod). The January and July ionograms are used to plot the dependences of the number of “sickle” type disturbances on the time of the day for the period from 1996 to 1992. A comparison with the scattering in an ionospheric F-layer for the same period is performed. A trend in the time series of the phenomenon observed is recorded. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 12, pp. 1455–1462, December, 1997.     

Acoustic-gravity waves in the earth’s atmosphere (review)

We present the modern theory of small-amplitude acoustic-gravity waves (AGWs) in the Earth’s atmosphere. Main attention is paid to the propagation and radiation of AGWs by different sources. We also consider problems of their dissipation, stability, and interaction with the ionospheric plasma. Basic methods of detecting the wave processes in the upper atmosphere in the AGW frequency range are briefly discussed. Experimental data on atmospheric inhomogeneities are compared with theoretical findings. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 1, pp. 3–25, January, 1999.     

Behavior characteristics of the index of middle-latitude F-spread

We present the results of analysis of data on ionospheric vertical sounding in Zimenki (Nizhny Novgorod) over the period from 1964 to 1992. The January ionograms are used for constructing the plots of daily indices of F-spread for an ionospheric layer. The dependence of the average monthly (January) index of F-spread on the solar activity is obtained. The index of F-spread is found to grow with time. The technogenic nature of this increase is assumed. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 3, pp. 322–327, March, 1997.     

Sounding of the ionosphere disturbed by the “Sura” heating facility radiation using signals of the GPS satellites

We present the results of experimental studies of the properties of the plasma-density disturbances created during heating of the ionospheric F₂ region by high-power HF radio waves radiated by the “Sura” heating facility (Radiophysical Research Institute, Nizhny Novgorod). These experiments are specific in that they were performed in a sunlit (daytime) ionosphere when the generation of ionospheric turbulence has specific features and the turbulence intensity level is low enough. The plasma-density disturbances induced by high-power HF radio emission were sounded by signals of the GPS satellites, the line of sight to which crossed different parts of the disturbed ionosphere region. Threshold powers of the excitation of artificial plasma-density variations as well as spatial, temporal, spectral, and energy characteristics of the generated disturbances are determined.     

On the frequency dependence of anomalous attenuation of sounding waves in the case of ionospheric modification by high-power radio emission

The dependence of anomalous attenuation of sounding waves on the frequency f is studied experimentally in the case of ionospheric F-layer modification by high-power radio emission. It is shown that anomalous attenuation increases for |f−f₀| < 20 kHz, f<f₀ (f₀ is the pump-wave frequency) and decreases for f>-f₀ compared with the frequencies that are more distant from f₀. This phenomenon is caused by plasma displacement and formation of a stepped electron-density profile in the region of upper hybrid resonance of the pump wave. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 8, pp. 966–977, August, 1998.     

On one feature of the F-spread phenomenon in the midlatitude ionosphere

We report on the results of observations of reflected SW signals by vertical sounding (VS) of the ionosphere in Zimenki, Nizhny Novgorod region, in the summers of 1994 and 1995. We discovered an anomalous increase in the multipath propagation of the received SW signals during ionospheric F-spread: The duration of a multipath reflected signal increased considerably when we used a highly directional antenna compared to the case of a weakly directional antenna. The fast amplitude fluctuation index increased with increasing delay of the reflected SW signals. The observations are interpreted in terms of a stochastic model of midlatitude F-spread as the phenomenon of multipath radio wave scattering (reflection) from large-scale electron density inhomogeneities under conditions of a strongly developed inhomogeneous structure of the ionosphere.Radiophysical Research Institute, Nizhny Novgorod. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, No. 10, pp. 1064–1070, October, 1995.     

On the reflection of a radiowave beam from a plasma layer with large-scale inhomogeneities

Using the method of parabolic equation (MPE), we obtain transfer equations for the mean field, the space-coherence function, and the ray intensity of a radiowave beam as it is reflected from a plasma layer with random inhomogeneities. The general solutions of these equations are found. Special attention is given to the case of radiowave beam reflection from a linear plasma layer with large-scale electron-density inhomogeneities. If a weakly directed transceiving SW antenna is used, the shortwave scattering can lead to a pronounced (of the order of 3 dB) decrease in the intensity of a vertical-sounding signal reflected from the ionospheric F2 layer only under the conditions of abnormally strong ionospheric electron-density perturbations. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 41, No. 8, pp. 955–965, August, 1998.     

On the excitation of the ionosphere by high-power radio waves in the geomagnetic equator region

We consider the features of the modification of the equatorial ionosphere by high-power radiowaves. A possibility for creating strong (compared to mid-latitude) quasi-periodic ionospheric F-layer irregularities, formed by the field of the high-power standing wave, producing artificial bubbles, and influencing the natural equatorial “bubbles” is discussed. The peculiarities of exciting the striction and thermal parametric instabilities in the equatorial ionosphere are considered. The problem of the modulation of the equatorial current jet is briefly discussed. Radiophysical Research Institute, Nizhny Novgorod, Russia; Swedish Institute of Space Physics, Uppsala Division, Uppsala, Sweden. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, Nos. 1–2, pp. 250–262, January–February, 1997.     

On the spectrum of large-scale inhomogeneities of the upper ionosphere

The possibility of measuring the large-scale turbulence structure of the upper ionosphere by vertical and oblique short-wave (SW) radio-sounding techniques is considered. General expressions have been derived for the phase fluctuation spectrum of a short-wave signal reflected at the ionospheric layer with an arbitrary regular permittivity profile and given spectrum of inhomogeneities. We have analyzed a number of particular cases which are most typical of phase measurements in the vertical and oblique SW radio-sounding of the randomly inhomogeneous ionosphere. It is shown that when these methods are used the phase fluctuation spectra of reflected signals may critically depend on the form of the ionospheric electron density profiles. The correct interpretation of the measurement data requires use of stations of synchronous vertical and oblique sounding to obtain proper ionograms and calculate the current spectra of a regular permittivity distribution of the ionosphere. Specific difficulties in interpreting the phase measurements of ionospheric inhomogeneity spectra by vertical and oblique radio-sounding methods are mentioned.Radiophysical Research Institute, Nizhny Novgorod. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, No. 7, pp. 653–659, July, 1995.     

The “Sura” facility: Study of the atmosphere and space (a review)

We present a short review of research using “Sura,” a multipurpose radio facility of the Radiophysical Research Institute of Nizhny Novgorod, which is aimed at studying space, the atmosphere, the Earth’s crust, and radio wave propagation and at developing new methods for diagnostics and monitoring of the environment. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 7, pp. 545–576, July 2007.     

Features of limb sounding of minor atmospheric constitutents at various microwave lines

We analyze the characteristics of radio emission from the middle atmosphere during limb sounding of minor gas constituents with rotational transitions of the molecules located in the atmospheric transparency windows 105–118 GHz and 180–210 GHz. Optimal frequencies and height ranges for the sounding of minor gases are found by numerical modeling for typical values of the receiver bandwidth. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 3, pp. 235–239, March 1999.     

Artificial periodic inhomogeneities and a model for the lower part of theD region

The measured height profiles of the relaxation time and amplitudes of artificial periodic inhomogeneities (API) in the ionospheric D region are compared with the model. It is shown that the height dependences of the relaxation time of APIs and the amplitude of the scattered signal can be explained taking into account the hieght profile of the atmosphere density. Most probably, the upper boundary of APIs in the D region is due to the increase in the atomic oxygen density and can serve as an altitude indicator. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 5, pp. 431–437, May 1999.     

Variations in the ionospheric wave perturbation spectrum during periodic heating of the plasma by high-power high-frequency radio waves

We present the results of spectral analysis of temporal variations in the Doppler frequency shift of the ionosphere-reflected signals from a high-frequency vertical ionospheric sounding radar located near the city of Kharkov in the days of exposure of the ionospheric plasma to the high-power radio emission of the Sura facility (Nizhny Novgorod) and in the reference day in the absence of such an exposure. It was established that the spectral characteristics of quasiperiodic variations in the Doppler frequency shift in the range of periods 10–60 min in the days of work of the facility and in the reference day differed significantly. This is considered as evidence in favor of the generation (amplification) of acoustic–gravity waves propagating at the ionospheric altitudes by high-power periodic high-frequency radiation of the Sura facility.     

Lowering of the threshold of nonlinear wave interaction in plasma with periodic inhomogeneities

We show that an absolute instability corresponding to the induced double Mandelshtam-Brillouin scattering develops at smaller amplitude of the incident wave if periodic inhomogeneities exist in the plasma. The lowering of the instability threshold is related to the increase of the wave amplitudes in the Bragg resonator that is formed in the medium with periodic inhomogeneities. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 7, pp. 704–708, July 1999.     

Review of features of stimulated electromagnetic emission (see): Recent results obtained at the “sura” heating facility

We present a short review of the features of the main components (DM, UM, NC, BC, BUM, and BUS) of stimulated electromagnetic emission (SEE). We discuss variations of these components in the case where additional X-mode heating is used. The experiments were performed at the “Sura” heating facility (Nizhny Novgorod, Russia) during the last few years. Radiophysical Research Institute (NIRFI), Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 7, pp. 635–640, July 1999.     

On the “caviton” signal,scattered by artificial ionospheric turbulence

The results of experimental investigations of the caviton signal (CS), scattered by artificial ionospheric turbulence are presented at the vertical sounding by short radiopulses. The dependences of the amplitude and the appearance time of CS on the power of the heating transmitter, the frequency of the probing one, and the virtual height of scattering are considered. The periodic generation of CS was observed with periods changing from fractions of a second up to several seconds.Radiophysical Research Institute, Nizhny Novgorod, Russia. Published in Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 37, No. 6, pp. 793–798, June, 1994.     

Artificial focusing system in the ionosphere

We propose a method for the creation of an artificial focusing radio wave system in the ionospheric E layer on the basis of the recombination effect by production of a bagel-shaped disturbance region in the ionosphere in the two-dimensional case and a two-band disturbance region in the one-dimensional case. Two-band disturbance of the ionosphere was achieved by appropriate reconstruction of the antenna system of the SURA facility. First experiments on the diagnostics of a focusing ionospheric system have been performed by observations from the NASA WIND space vehicle. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, Nos. 1-2, pp. 101–110, January–February, 1997.     

Frequency correlation of fluctuations of short-wave signals in the theory of refractive scattering of radiowaves in the ionosphere

We consider the problem of frequency correlation of phase fluctuations of HF signals reflecte from a turbulent ionospheric layer with an arbitrary profile of electron density in vertical and oblique sounding of the ionosphere. Expressions for evaluation of the coherence band of HF signals reflected from a randomly inhomogeneous ionosphere are obtained. Calculation results are compared with corresponding calculations of frequency correlation of fluctuations of HF radiowaves in Buker's theory of refractive scattering of radiowaves. It is shown, in particular, that the influence of splitting of rays for waves with different frequencies in an inhomogeneous ionosphere on the frequency distortions of HF signals prevails compared with the phenomenon of frequency decorrelation of fluctuating HF signals propagating in a free space beyond a turbulent ionospheric layer.Radiophysical Research Institute, Nizhny Novgorod. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, No. 9, pp. 893–900, September, 1995.