N. A. Mityakov

Artificial ionospheric turbulence (review)

This study is an analysis of artificial ionospheric turbulence (AIT) arising near the level at which a powerful wave is reflected with ordinary polarization. AIT is an inhomogeneous structure in the ionosphere with a size on the order of centimeters or tens of kilometers and with characteristic frequencies from a fraction of a hertz (aperiodic inhomogeneity) to several megahertz (plasma waves). The authors are primarily concerned with small-scale artificial ionospheric turbulence (SAIT), i.e., with inhomogeneities that are greatly extended along the geomagnetic field with transverse dimensions that are less than the wavelengths of the perturbing waves - the pumping waves (PW) - in a vacuum.

Hysteresis effect in the artificial excitation of inhomogeneities in the ionospheric plasma

A hysteresis effect is discovered in the dependence of the scattering cross section of artificial ionospheric inhomogeneities on the intensity of the radio waves exciting them. The thresholds for the excitation and cutoff of the plasma instability are determined and the dependence of the magnitude of its fluctuations on the power of the exciting transmitter is established.

Electron acceleration in the presence of parametric heating of a bounded layer of plasma

The acceleration of superthermal electrons by parametric turbulence in a bounded layer of plasma is considered. It is shown that an essential role is played by the effects of turbulent scattering of the superthermal particles out of the interaction region. These effects are due to the process of stochastic motion of the electrons in the course of interaction with the plasma turbulence. These effects lead to a build-up of superthermal particles in the interaction region, and they lead to a significant increase in the efficiency of acceleration. The authors use a theory they developed to explain the observed effects of electron acceleration in experiments which have to do with parametric heating of the ionosphere.

Induced wave scattering in ionospheric plasma

Abstract Parametric excitation of plasma oscillations in the ionosphere by an electromagnetic wave near the reflection level has been considered. The spectrum of plasma waves forms as a result of action of the source (a pump wave), non-linear transfer towards large scales and damping. The results of the theory are in satisfactory agreement with the experiment.

Frequency characteristics of the action of powerful radio-frequency radiation on the ionospheric F layer

The results of an investigation of the effect of artificial ionospheric nonuniformities on the characteristics of LFM signals with vertical and oblique sounding of the ionosphere are presented. A classification of the effects observed on ionograms from vertical and oblique-sounding LFM ionosonde, owing to the effect of artificial nonuniformities of different scale, is given. It was found that powerful beams of radio waves have a characteristic effect on the ionospheric plasma under conditions when moving ionospheric disturbances appear.

Study of wind characteristics at heights of 200 to 800 meters using a decimeter sodar

The results of the experiment carried out in July–August 1997 using a two-position sodar are reported. Different types of intensity and spectrum variations of scattered acoustic signals have been obtained. The possibilities of using the sodar for the study of atmospheric turbulence and search of signals caused by “Fresnel” scattering from “plane” irregularities are discussed.

Study of small variations of troposphere parameters by the radioacoustic sounding method

We consider a method based on the study of signal amplitude and phase variations in the radioacoustic sounding (RAS) of the atmosphere for the diagnostics of dynamical and wave processes in the troposphere. We give experimental data on phase variations of the RAS signal from scan to scan in daytime and nighttime sessions. Variations of the signal phase with characteristic time greater than 40 min are likely due to the passage of internal gravity waves (IGW) through the sounding region. The experimental data are in good agreement with the results of computer simulation of IGW propagation.

On the nature of middle-latitude F-spread

The results of a special experiment to study the statistics of short-wave signals reflected from the ionosphere during F-spread conducted in the first half of 1994 at the proving ground of the Scientific-Research Radio-Physics Institute at Zimenki of the Nizhny Novgorod region are presented. The dependence of the index of amplitude fluctuations on the reception bandwidth was studied. The experiment results are compared with existing theoretical concepts of the origin of F-spread. The experiment favors the hypothesis that middle-latitude F-spread is result of the multiple-ray nature of short-wave signals reflected from the large-scale quasi-regular inhomogeneous structure of the ionosphere.

Some results of synchronous experimental study of artificial F-spread at radiophysical test sites in nizhny novgorod province

We show some results of experiments on synchronous sounding of the ionosphere by short-wave signals at the Radiophysical Research Institute’s test site in Zimenki and Vasil’sursk, Nizhniy Novgorod province, during ionospheric modification by high-power short radiowaves from transmitters of the “Sura” facility in Vasil’sursk. In the course of experiments we proved directly the decisive role of large-scale inhomogeneities of the ionospheric plasma with dimensions of from several kilometers to several dozens of kilometers in the formation of artificial F- spread. The small-scale inhomogeneities with dimensions smaller than 1 km, which are localized in a relatively thin layer near the reflection level of a high-power short radiowave, emerged only at sounding waves, propagating (reflected) in the immediate vicinity of the center of the heating region.

THE ROLE OF ATMOSPHERIC TEMPERATURE GRADIENTS AND WINDS FOR ESTIMATING THE ENERGY POTENTIAL OF RADIO-ACOUSTIC SOUNDING SYSTEMS

We present the theory of radio-acoustic sounding (RAS) of the atmosphere allowing for the dependence on temperature, altitude, and wind. For the case of a linear temperature profile, we obtained expressions for the received signal power. Since the acoustic wave front differs from the sphere if the temperature gradient is allowed for, we can introduce the notion of projector (Fresnel) and Fraunhofer regions. In the Fresnel region, the size of the diffraction spot on the earth is determined by radar antenna dimensions and the received signal power is proportional to z−2. In the Fraunhofer region, the spot size is greater than the antenna dimensions and the power is proportional to z−6. The existing RAS facilities work in the projector region. This can be used as a basis for developing a new method of diagnostics of a large-scale inhomogeneous atmospheric structure, including wave disturbances.