Radiowave fluctuations in the polar ionosphere on the satellite-to-satellite paths under high solar activity

We analyze ionospheric fluctuations of decimeter radio waves on occultation polar paths between the navigational GPS satellites and the satellite CHAMP. Time dependences of the variance of the signal amplitude and amplitude fluctuation spectra under high solar activity in October–November 2003 are presented. The behavior of the signal amplitude fluctuations during occultation ionospheric sounding in the polar regions in different time of the day and in the equatorial regions in the daytime are considered. Radio-wave fluctuations are related to the solar-activity manifestations. It is shown that during strong solar-flare activity, intense small-scale plasma irregularities are excited in the polar ionosphere. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 3, pp. 185–193, March 2006.     

New Results of Studying the Lower Ionosphere by the Method of Resonance Scattering of Radio Waves from Artificial Periodic Inhomogeneities

We present the results of studying the lower ionosphere in 2000–2004 at the “Sura” heating facility by the method of resonance scattering of radio waves from artificial periodic inhomogeneities of the ionospheric plasma. Experimental data on a study of the sunset–sunrise phenomena in the ionospheric D region and the possibility of determining the concentrations of atomic oxygen and excited molecular oxygen are discussed. The results of studying the sporadic layers of ionization are presented and the method for a study of ion composition of the E_s layer is discussed. Data of the August 2004 experiments on a study of the influence of heating the ionosphere on the E_s layer and characteristics of artificial periodic inhomogeneities are presented. Prospects for further research are discussed. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 9, pp. 757–771, September 2005.     

Lower polar ionosphere during a solar flare as revealed from radiooccultation data in satellite-to-satellite links

It is shown that there are typical variations in the amplitude and phase of decimetric radio waves in satellite-to-satellite links due to variations in the polar ionosphere structure. The altitude profiles of the electron number density and vertical size of the ionospheric sporadic structures in the nighttime polar regions during the period of intense solar activity in October 25 to November 09, 2003 are estimated. Correlation between the the ionosphere characteristics and the solar-wind parameters is discussed. It is noted that the effect of energetic-particle precipitation due to the influence of shock waves of the solar wind is the main factor responsible for strong variations in the nighttime polar ionosphere. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 52, No. 3, pp. 181–191, March 2009.     

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.     

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.     

Oblique chirp sounding of the modified ionosphere. Experiment and simulation

We present the results of experimental studies of the influence of artificial ionospheric disturbances on HF signals used for oblique sounding of the disturbed volume. The measurements have been performed by a chirp ionosonde over the path Yoshkar-Ola-“Sura”-niznhy Novgorod with length 234 km. We found the 2F2 mode to disappear (attenuation up to 20 dB) when the ionosphere is influenced by a vertical powerful radiation in the ordinary mode with long (15 min each) heating and pause intervals. Modeling of the observed effect was carried out. The calculations agree well with experimental data if the traveling ionospheric disturbances (TID) with vertical and horizontal scales l_z∼20 km and l_x∼50 km, respectively, and the relative disturbance of the electron density δN∼0.2–0.3 are amplified (generated) during the ionosphere heating. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 4, pp. 303–313, April 1999.     

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.     

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.     

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.     

Studies of the Irregular Structure of the Ionosphere using Scattering of Radio Waves on Artificial Periodic Inhomogeneities

We present new results of our studies of the irregular structure of the ionosphere using artificial periodic inhomogeneities (APIs) of the ionospheric plasma. The observations were carried out from 9:00 to 17:00 in August 10–12, 1999 with a height step of 0.7 km and digital registration and real-time processing of the signal quadratures. It is shown that in many cases, the amplitude of the scattered signal is determined by the interference of radio waves scattered on APIs and on natural ionospheric formations including sporadic layers and large-scale natural irregularities. This allows one to study the irregular structure of the lower ionosphere by analyzing height-time dependences of the amplitude and phase of the scattered signal.     

Sunset-sunrise characteristics of sporadic layers of ionization in the lower ionosphere observed by the method of resonance scattering of radio waves from artificial periodic inhomogeneities of the ionospheric plasma

We present the results of studying the sporadic layers of ionization in the lower ionosphere observed in the sunset-sunrise time during the summer months of 2000 and 2001. Measurements were performed at the Sura heating facility of the Radiophysical Research Institute (Nizhny Novgorod, Russia). Based on the analysis of the altitude-time dependences of the amplitude, relaxation time, and phase of the scattered signal, we obtain new data on the formation and dynamics of the evening and nighttime mid-latitude sporadic E layer, present the results of measuring the velocity of the plasma vertical motion, and estimate the relative molecular mass and total number density of metal ions whose pile-up due to the wind shear can cause the formation of the observed sporadic layers.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 1, pp. 16–32, January 2005.     

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. Radiophysical Research Institute, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 40, No. 11, pp. 1355–1364, November, 1997.     

Optical and magneto-optical properties of Fe/Cu multilayered films: Influence of the modulation period and the bcc-fcc phase transition in iron

The optical and magneto-optical properties of multilayered film samples of the Fe/Cu system prepared by high-frequency sputtering on an Si(100) substrate are studied by ellipsometry and by measuring the equatorial Kerr effect (the δ _p effect) in the spectral range 0.25–7 μm. The optical characteristics, the plasma frequency ω _p and the relaxation frequency γ ₀ of the conduction electrons, and the δ _p effect are found as functions of the modulation period D=12.5–100 Å. Anomalous behavior of the optical and magneto-optical characteristics is discovered in short-period Fe/Cu structures. The results are discussed within a phenomenological theory of optical and magneto-optical properties for layered structures. Several factors, such as the indirect exchange interaction between the iron layers, the presence of a transition layer on the internal boundaries, the possible “magnetizing” of copper, and the formation of an fcc iron phase in the thin layers, are taken into account in the analysis of the experimental data. Zh. éksp. Teor. Fiz. 112, 1694–1709 (November 1997)     

On small-scale plasma inhomogeneities of the traveling ionospheric disturbances

We report on the results of the first special experiment on radio sounding of the midlatitude ionosphere by signals from in-orbit satellites at a frequency of 150 MHz under quiet geophysical conditions. Along with the conventional correlation processing, fractal processing of the received signals was also performed. Using the fractal approach, we obtained first data on the sources and generation mechanisms of small-scale plasma inhomogeneities of the traveling ionospheric disturbances (TIDs) in the upper ionosphere. It is noted that the phenomenon of nonlinear “ breaking” of the acoustic-gravity waves entering the ionosphere from the underlying atmosphere plays the crucial role in the formation of plasma inhomogeneities of the TIDs. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 7, pp. 561–569, July 2006.     

Modification of the earth’s ionosphere by high-power HF radio emission: Artificial periodic inhomogeneities and the sporadic <Emphasis Type="Italic">E</Emphasis> layer

We present the results of new studies of the sporadic E layer in the case of heating of the ionosphere by high-power HF radio emission. The measurements were performed at the “Sura” heating facility. Ionosphere was modified by high-power radio emission from the “Sura” facility and was sounded by the probing radio waves of the same frequency and mode. The heating of the ionosphere resulted in the formation of artificial periodic inhomogeneities, and an increase in the intensity of all signals scattered by the D, E, and F regions and the sporadic E layer by 5–20 dB was observed. The increase was observed during heating of the ionosphere by each magnetoionic component, but was smaller for heating by an ordinary-mode wave. This effect was resonant and disappeared as a result of the frequency detuning down to 85 kHz. During the ionospheric modification, the signal-intensity increased due to modulation of the natural profile of the electron number density by the artificial periodic structure. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 50, No. 8, pp. 695–708, August 2007.     

Oblique Sounding and Modeling of the Ionospheric HF Channel

We present the results of experimental studies of the distance-frequency and amplitude-frequency characteristics of the ionospheric HF channel on mid-latitude paths of oblique chirp sounding. It is shown that the maximum observed frequencies (MOFs) are subject to short-period variations with the quasi-periods from 30 min to 2 h.The amplitude of the MOF variations reaches 2 MHz and can increase up to 5–8 MHz on the Cyprus—Rostov-on-Don one-hop path in the sunrise-sunset time. It is established that the MOF fluctuations are accompanied by pronounced “cusp” features occurring in the upper rays and moving with time to the region of shorter delays, i.e., from lower to higher frequencies. The amplitude-frequency characteristics of individual propagation modes undergo deep fluctuations (up to 20–30 dB)whose quasi-period and depth depend on the frequency. It is shown that the appearance of fluctuations is caused by interference of the unresolved rays within the limits of one propagation mode. Based on the modeling, it is shown that “cusps” in oblique-sounding ionograms are due to the influence of traveling ionospheric disturbances (TIDs). The TID parameters are estimated. It is shown that conditions of the formation of “ cusps” in the distance-frequency characteristics depend on the TID amplitude, the wavelength of the disturbance wave, and the direction of its phase front with respect to the propagation path. The effect of quasi-regular frequency modulation of the Pedersen mode with a period of 250–300 kHz on the Cyprus-Rostov-on-Don chirp-sounding path is found. Altitude stratification of the ionosphere near the F-layer maximum, which is responsible for the focusing and defocusing of the Pedersen mode, is estimated. It is established that the stratification scale amounts to approximately 200–250 m. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48, No. 6, pp.455–471, June 2005.     

On specific features of diurnal variations in characteristics of the diagnostic stimulated electromagnetic emission and their relation to the evolution of artificial ionospheric irregularities

We analyze variations in characteristics of the diagnostic stimulated electromagnetic emission of the ionosphere in the evening hours including the times of sunset both on the Earth’s surface at the observation point and in the ionosphere over it. It is found that an increase in typical times of evolution of the diagnostic emission begins to be recorded just before the sunset on the Earth’s surface when the ionosphere is illuminated and its parameters are not significantly changed yet. We state that the typical times of evolution of the diagnostic emission increase when the pump-wave frequency approaches the critical frequency of the ionospheric F₂ layer, but such an effect is not as significant as when passing from the illuminated to the unilluminated ionosphere. It is established that at the stage of diagnostic sounding the pump-wave pulse power does not exert any notable influence on the first (fast) stage of relaxation of small-scale artificial ionospheric irregularities, but can increase the decay time of the irregularities at the second (slow) stage of relaxation. Capabilities of the method for a study of artificial plasma turbulence using the diagnostic stimulated electromagnetic emission are discussed. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 4, pp. 273–286, April 2008.     

Parametric excitation of an extremely low-frequency radio pulse by an extragalactic gamma-ray burst on December 27, 2004

We simulate an electromagnetic pulse excited by a sharp descent of the charged upper wall of the Earth–ionosphere cavity. The ionosphere descent by 20 km was detected over the dayside Earth’s hemisphere during a giant extragalactic gamma-ray burst in the constellation of Sagittarius (SGR 1806–20). We show that a sharp change in the ionosphere altitude can cause a discrete pulse of extremely low-frequency radiation with the spectrum having some specific features and the amplitude significantly exceeding the natural regular noise background. The time of arrival of the radio pulse to an observer coincides with the gamma-burst time.     

Ionospheric response to the solar eclipse on March 29, 2006

In the present work, results of vertical sensing of the ionosphere at the Klyuchi (Novosibirsk) and Arti (Ekaterinburg) Geophysical Observatories during the solar eclipse on March 29, 2006 are given. The maximum eclipse was observed in Novosibirsk at 11:43 UT; the obscuring phase was 92%. A maximum obscuring phase of 80% was observed at the Arti Georhysical Observatory at 11:32 UT. The results obtained are compared with the analogous data obtained in the preceding and next days as well as with the data of many-year observations on March 28, 29, and 30. The results obtained demonstrate that the eclipse affects most strongly the characteristics of the F layer. The maximum variations of the critical frequency f₀F2 were delayed by about 10 min from the maximum eclipse phase, relaxation started half an hour after the maximum eclipse phase, and the frequency decreased at most by 1.5 MHz. A decrease in the critical frequency of the F1 layer has a greater delay and smaller amplitude. The results obtained are in good agreement with previous measurements. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 68–72, September, 2006.     

On the Problem of True Values of the Spectrum Indices for Small-scale Ionospheric Turbulence

We consider the problem of obtaining reliable values of the local-spectrum indices of the electron number density fluctuations for small-scale ionospheric turbulence. It is shown that the use of a multifractal analysis in combination with the synchronous correlation processing of the received signals in the experiments on remote radio sounding of the ionosphere by satellite signals permits one to solve the posed problem. In this case, the true values of the local-spectrum indices of small-scale ionospheric turbulence, which are measured in such specialized experiments under natural conditions and during modification of the ionosphere by high-power HF radio emission, can differ notably from their standard values obtained within the framework of the classical method of radio scintillations, in which only correlation processing of the data is used. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 7, pp. 571–574, July 2008.