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.     

Variations in the parameters of scattered signals and the ionosphere connected with plasma modification by high-power radio waves

We describe the results of using the incoherent scatter technique to observe time-altitude variations in regular parameters of the ionospheric plasma and wave disturbances, which accompanied periodic modification of the near-Earth plasma by radio waves emitted by the “Sura” facility. A distinctive feature of the experiments was that the processes in the ionosphere were diagnosed at a distance of about 1000 km from the facility. It was found that the spectrum composition of wave disturbances in the electron density was changing noticeably during the active experiment. Quasi-periodic processes in the ionosphere were observed with a delay of about 40–60 min. The relative amplitude of wave disturbances was equal to 0.02–0.10, and the periods were equal to 30, 60, 120, and 150–180 min. The observed effect can be explained by the generation and/or amplification of traveling ionospheric disturbances. The results of theoretical estimations agree well with the observational data.     

On the effects observed during modification of the earth’s upper ionosphere by high-power short radio pulses

We report on the results of studies of the evolution of artificial ionospheric turbulence (AIT) excited by short pulses of high-power short-wave O-mode radio emission in the ionospheric F region. On the basis of the obtained experimental data, it is assumed that the streams of thermal and suprathermal electrons generated in the regions of resonant interaction between a high-power radio wave and the plasma and propagating along the geomagnetic field stimulate the development of plasma perturbations far away from the primary-turbulence regions. Specific features of the measurement procedure are considered, an empirical model of the observed phenomena is developed, and possible problems in the further studies are outlined. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 8, pp. 643–663, August 2006.     

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.     

HF ducting control due to modification of the ionosphere by powerful radiation

The conditions are experimentally investigated for ionospheric duct excitation due to radio wave refraction on the electron density gradient as well as for the escape of the waveguide modes to the Earth at the expense of the radio wave aspect scattering on artificial ionospheric turbulence. The geophysical conditions for effective HF ducting control are determined. The temporal and frequency characteristics of the escaping mode are evaluated.Mari Polytechnic Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 36, No. 5, pp. 390–397, May, 1993.     

Propagation of LF/VLF radio waves below a nonuniform ionosphere

Summary A simple approach to LF/VLF field calculations for a nonuniform, isotropic ionosphere is developed. The theory introduces two modifications to the standard wave hop theory: namely the use of local reflection coefficients and the use of an average reflection height for the path integrals. Sample calculations, including a comparison with measured results, are presented.

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Riassunto Si sviluppa un semplice approccio di calcoli di campo LF/VLF per una ionosfera isotropica non uniforme. La teoria introduce due modifiche alla teoria standard del balzo delle onde: cioè l'uso di coefficienti locali di riflessione e l'uso di un'altezza media di riflessione per gli integrali di percorso. Si presentano calcoli campione, compreso un confronto con i valori risultati.

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Резюме Развивается простой подход для вычислений LF/VLF поля в неоднородиой изотропниой ионосфере. В этом подходе вводится две модификации в стандартную теорию рассеяния волн. Приводятся простые вычисления, включая сравнение с экспериментальными результатами.

     

Study of large-scale irregularities generated in the ionosphericF-region by high-power HF waves

Experimental studies of the features of artificial ionospheric turbulence was performed at the “Sura” heating facility in August 1998 using numerous diagnostic tools, such as scintillation, chirp-sounding, backscattering, and stimulated electromagnetic emission (SEE) measurements, as well as sounding a HF-disturbed volume (DV) by probing waves. It has been found that generation of strong artificial large-scale irregularities (ALSIs), which manifest themselves through the F-spread on ionograms, scintillations of the satellite signal propagated through the DV, and amplitude fluctuations of the probing wave sounding the DV, is observed not only for an overdense heating, at fo≤foF₂, but also at higher frequencies fo>foF₂≥f _uh (here fo is the pump-wave frequency, foF₂ is the critical frequency of the F₂-layer for O-mode electromagnetic wave, and f _uh is the plasma frequency at the upper-hybrid resonance height). This means that transfer of the pump-wave energy in the plasma due to the development of thermal parametric (resonance) instability, rather than thermal self-focussing instability, plays the key role in the ALSI generation in the case where the O-mode HF wave is used for the overdense heating. This conclusion is also confirmed by the fact that the ALSI generation is suppressed in the gyroharmonic frequency range, which is similar to the well-studied quenching of the downshifted maximum (DM) in SEE spectra. In this paper, we discuss new ALSI features revealed by the measurements, as well as the limits by which one can control the ALSI spectrum using complex pumping schemes. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 43, No. 6, pp. 497–519, June, 2000.     

The polar-ionosphere phenomena induced by high-power radio waves from the spear heating facility

We present the results of experimental studies of specific features in the behavior of small-scale artificial field-aligned irregularities (AFAIs) and the DM component in the spectra of stimulated electromagnetic emission (SEE). Analysis of experimental data shows that AFAIs in the polar ionosphere are generated under different background geophysical conditions (season, local time, the presence of sporadic layers in the E region, etc.). It is shown that AFAIs can be excited not only in the F region, but also in “thick” sporadic E _s layers of the polar ionosphere. The AFAIs were observed in some cycles of heating when the HF heater frequency exceeded the critical frequency by 0.3–0.5 MHz. Propagation paths of diagnostic HF radio waves scattered by AFAIs were modelled for geophysical conditions prevailing during the SPEAR heating experiments. Two components, namely, a narrow-banded one with a Doppler-spectrum width of up to 2 Hz and a broadband one observed in a band of up to 20 Hz, were found in the sporadic E _s layer during the AFAI excitation. Analysis of the SEE spectra shows that the behavior of the DM component in time is irregular, which is possibly due to strong variations in the critical frequency of the F ₂ layer from 3.5 to 4.6 MHz. An interesting feature observed in the SPEAR heating experiments is that the generation of the DM component was similar to the excitation of AFAIs when the heater frequency was up to 0.5 MHz higher than the critical frequency. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 11, pp. 939–950, November 2008.