Sura Facility Research Articles

The 630 nm and 557.7 nm Airglow During HF Ionosphere Pumping by the SURA Facility Radiation for Pump Frequencies Near the Fourth Electron Gyroharmonic

We present the results of analysis of the dependence of the ionospheric airglow in the red (630 nm) and green (557.7 nm) lines of atomic oxygen on the pump-wave frequency f 0 near the fourth electron gyroharmonic 4f ce. The experimental data were obtained in 2012 using the SURA heating facility. Stimulated electromagnetic emission spectra were used to determine the relation between f 0 and 4f ce. It is found that at f 0 > 4f ce and δf = f 0 − 4f ce ≈ 15–20 kHz the red-line airglow intensity is about a factor of 1.5 higher for the magnetic zenith pumping (when the pump beam is inclined 12° south of the magnetic field direction) than for the vertical pumping. In the green line for the same offsets δf, the airglow was recorded with confidence only during magnetic zenith pumping. During vertical pumping, no regular dependence of the red-line airglow intensity on δf in the range −15 < δf < 280 kHz was obtained, while the green-line airglow was observed at 15 < δf < +5 kHz and 230 < δf < 280 kHz. In the red line during vertical pumping, a change from the artificial airglow generation to the ionospheric background suppression was detected when the F-layer cutoff frequency was decreased. During magnetic zenith pumping, a wide (about 30°) background suppression zone was observed around the airglow spot with an about 6° angular width.

Geomagnetic Pulsation Amplitude and Spectrum Variations Accompanying the Ionospheric Heating by High-Power Radio waves from the Sura Facility

Aperiodic and quasiperiodic variations in the geomagnetic pulsation amplitude in a range of periods from 40 to 1000 s, which accompany the quasicontinuous and periodic impact on the ionospheric plasma by high-power radio waves from the SURA facility near Nizhny Novgorod (Russia) were recorded near Kharkov (Ukraine) using a magnetometer–fluxmeter. The main parameters of aperiodic and quasiperiodic disturbances of the geomagnetic field are determined. The mechanisms for generation and propagation of detected disturbances are discussed.

Small-Scale Turbulence of the Earth’s Magnetosheath

We present the results of experiments on reception of the Sura facility signals in the 9-MHz range using the WIND spacecraft. The technique of determining the temporal spectrum of the Earth’s magnetosheath plasma irregularities with less than 100-km scales based on the radio scintillation spectrum in terms of the weak scattering theory is proposed and implemented. Using the in situ measurements of the electron number density onboard spacecraft with a temporal resolution of about 3 s, it has been found that the inner scale of the magnetosheath turbulence varies within 10–90 km with a mean value of about 30 km.

Properties of the ULF/VLF Signals Generated by the Sura Facility in the Upper Ionosphere

The results of studying the generation of low-frequency radiation in the ionosphere affected by high-power modulated HF radiation of the Sura facility are presented. A large amount of data on characteristics of the ULF/VLF artificial signals observed in the night time, which indicate the manifestation of a new generation mechanism not related to the quasistationary ionospheric current modulation effect, have been obtained for the first time at the mid-latitudes. The results of studying the dependence of the signal value on the beam inclination of the pump wave and the distance to the observation point from the facility are presented. It is shown that the signals can be both right- and left-hand polarized depending on the level of geomagnetic activity. The measured time delay of the ULF signal indicates the location of the source at the F-layer maximum. Interpretation of the observed characteristics of artificial low-frequency signals based on a ponderomotive excitation mechanism of the diamagnetic ring current around the HF radiation beam at a modulation frequency agrees with the main results of the experiment.

Structure of the Electric Field of a High-Power Radio Wave in the Outer Ionosphere

The electric field of a high-power HF radio wave radiated by the Sura facility was measured using onboard instruments of the French microsatellite DEMETER at altitudes of 670 km. The data analysis shows that the high-power radio wave passes to the outer ionosphere under conditions where the difference between the cutoff frequency and the pump-wave frequency does not exceed 0.5–0.7 MHz in the undisturbed ionosphere. Energy and spatial characteristics of the high-power radio wave transmitted through the ionosphere are determined. A possible mechanism explaining such a penetration to the supercritical plasma is discussed.

Features of Propagation of the Acoustic-Gravity Waves Generated by High-Power Periodic Radiation

We present the results of the bandpass filtering of temporal variations of the Doppler frequency shift of radio signals from a vertical-sounding Doppler radar located near the city of Kharkov when the ionosphere was heated by high-power periodic (with 10 and 15-min periods) radiation from the Sura facility. The filtering was done in the ranges of periods that are close to the acoustic cutoff period and the Brunt—Vaisala period (4–6, 8–12, and 13–17 min). Oscillations with periods of 4–6 min and amplitudes of 50–100 mHz were not recorded in fact. Oscillations with periods of 8–12 and 13–17 min and amplitudes of 60–100 mHz were detected in almost all the sessions. In the former and the latter oscillations, the time of delay with respect to the heater switch-on was close to 100 min and about 40–50 min, respectively. These values correspond to group propagation velocities of about 160 and 320–400 m/s. The Doppler shift oscillations were caused by the acoustic-gravity waves which led to periodic variations in the electron number density with a relative amplitude of about 0.1–1.0%. It was demonstrated that the acoustic-gravity waves were not recorded when the effective power of the Sura facility was equal to 50 MW and they were confidently observed when the effective power was increased up to 130 MW. It is shown that the period of the wave processes was determined by the period of the heating–pause cycles, and the duration of the wave trains did not depend on the duration of the series of heating–pause cycles. The data suggest that the generation mechanism of recorded wave disturbances is different from the mechanism proposed in 1970–1990.

Relaxation Time of Artificial Periodic Irregularities of the Ionospheric Plasma and Diffusion in the Inhomogeneous Atmosphere

We consider diffusion of the ionospheric-plasma irregularities as applied to the problem of experimental determination of the lower-ionosphere parameters by artificial periodic irregularities of the electron number density. A rigorous solution to the problem of diffusion of one-dimensional plasma irregularities in a weakly ionized medium, whose diffusion coefficient exponentially decreases with the altitude, is obtained. The Green’s function for this problem is found. Three parameters are taken into account in the solution, namely, the size of the region occupied by the irregularities, the size of the irregularities, and a typical spatial scale of the e-fold decrease in the diffusion coefficient. Theoretical relaxation times of the irregularities as functions of these parameters are analyzed. Calculated relaxation times are compared with the times measured in the observation of the artificial periodic irregularities created by the SURA facility. Calculated relaxation times of these irregularities are in good agreement with the observed values.

Radio Interferometric Research of Ionosphere by Signals of Space Satellites

AbstractSince 2012, the Radiophysical Research Institute and the Lobachevsky State University at Nizhny Novgorod, Russia and the Ventspils International Radio Astronomy Centre at Irbene, Latvia are making radio interferometric experiments on study of ionosphere parameters in a quiet (natural) state of medium and research of artificial turbulence of the ionosphere, heated by the emission from the SURA facility. Remote diagnostics of the ionosphere is implemented using a method of radio sounding by signals of navigation satellites in combination with the Very Long Baseline Interferometry (VLBI) method. As a result of spectral and correlation analysis, interferometric responses of the two-element (RRI–UNN) and three-element (RRI–UNN–Irbene) interferometers were received by observations of 12 satellites of the navigation systems GLONASS and GPS. Here the first results are reported.

Auroral activity caused by high-power radioemission from the SURA facility

A series of experimental modifications of the ionosphere in the HF range, performed at the SURA facility base, together with optical measurements onboard the International Space Station (ISS), indicated that such impacts on the ionosphere are effective when the facility operational frequency is higher than the critical plasma frequency (for the main ionospheric F2 layer). The experimental measurements were supported by measurements at ground-based observatories, ISS, and the Demeter and GPS satellites. The analysis results of the entire data set are presented. The ray HF radio tracing for the experiment of October 2, 2007, has been calculated, and it has been indicated that the ionosphere to the north of the facility up to 60°–62° N latitudes was irradiated by the facility beam (the effects of ray redistribution and refocusing) due to refraction on the gradient of the F2 layer critical frequencies. An analysis of the ground-based and satellite measurements (both in the vicinity of a heater and in the magnetically conjugate region) indicates that it is possible to trigger a substorm in experiments with the Sura heating facility.

Infrasound oscillations in the ionosphere affected by high-power radio waves

We present the results of filtering in the range of periods 5.6–6.7 min of temporal variations in the Doppler frequency shift of the ionosphere-reflected radio signals from the high-frequency vertical ionospheric-sounding radar located near the city of Kharkov during ionospheric plasma modification by high-power periodic (with 6-min period) radio waves of the Sura facility. It is found that switching on and off a series of pulses with 3-min duration and the same pause launched a damped wave process with 6-min period, a delay time of about 30–50 min, and an apparent propagation velocity of about 320–530 m/s. The quasi-periodic variation amplitude of the Doppler frequency shift was 10–40 MHz. The corresponding relative-perturbation amplitude of the electron number density was about 0.1–0.3%. Detected oscillations is evidence that damped infrasound density waves can be generated in the upper atmosphere.

Results of radiophysical studies of the wave processes in the ionospheric plasma during its heating by high-power radio emission of the Sura facility

We present the results of observations of the wave disturbances in the ionospheric F region over the city of Kharkov, which accompanied the impact on the ionosphere by high-power radio emission of the Sura heating facility located about 960 km from the observation site. Enhancement of the wave activity in the heater operation intervals is detected. A 1.5–4-fold increase in the relative amplitude of the wave disturbance with a period of about 30 min close to the Sura operation mode at altitudes 160–235 km is revealed. The parameters of this disturbance are evaluated. It is shown that this effect can be due to the propagation of internal gravity waves in the atmospheric waveguide having about 200 km in height and 80–100 km in width. The efficiency of comprehensive analysis of the experimental data which we used to reveal and estimate the parameters of the wave disturbances with a small (a few percent) relative amplitude is demonstrated.

Applications of broadband radio signals for diagnostics of electron density profile dynamics and plasma motion in the HF‐pumped ionosphere

A technique for studying inhomogeneous structure and motions in the ionosphere by measurements of the amplitude and phase characteristics of wideband radio pulses is developed and demonstrated in investigations of the HF‐pumped ionospheric volume above the Sura facility. For the study of the vertical structure (electron density profile and vertical velocities) with high altitude and temporal resolution, a Tikhonov regularization algorithm for the solution of the inverse problem using phase sounding data is implemented. Horizontal velocity data are obtained by means of a correlation analysis of the reflected signals received by the diversity technique. The application of the technique described allows measurement of the HF pump‐induced modifications of the electron density profile, particularly the plasma expulsion from the plasma resonance and upper hybrid resonance regions, with high accuracy.

Aperiodic large-scale disturbances in the ionospheric E region stimulated by high-power HF heating

We describe the observation results of ionospheric disturbances at altitudes of 100 to 140 km, which occurred at a distance of about 1000 km from the Sura facility. The observations have been made using the incoherent scatter radar located near Kharkov. The electron density increase by 10–70 % had a temporal duration of 10–20 min and accompanied the high-power HF heating. The time of disturbance evolution was about 10 min. The observation effect can be explained by the intensification of the subsystem coupling in the ionosphere–magnetosphere–upper atmosphere– ionosphere system, which leads to a precipitation of energetic electrons from the magnetosphere. Parameters of the precipitating particles and precipitation-produced ionization are estimated.

Airglow during ionospheric modifications by the sura facility radiation. experimental results obtained in 2010

We present the results of studying the structure and dynamics of the HF-heated volume above the Sura facility obtained in 2010 by measurements of ionospheric airglow in the red (λ = 630 nm) and green (λ = 557.7 nm) lines of atomic oxygen. Vertical sounding of the ionosphere (followed by modeling of the pump-wave propagation) and measurements of stimulated electromagnetic emission were used for additional diagnostics of ionospheric parameters and the processes occurring in the heated volume.

Studying characteristics of the large-scale ionospheric irregularities induced by high-power HF radio emission with GPS diagnosis

UDC 533.9 We present the results of experimental studies of artificial large-scale irregularities of the ionospheric electron number density with dual-frequency GPS diagnosis. The total electron content was analyzed in the GPS signal trajectory when the satellites passed over the heated region. Spectral composition of the observed variations was determined by wavelet analysis. Characteristic scales of artificial irregularities of the electron number density in the F layer are estimated. It is experimentally proved that the irregularities remain for at least 15–20 min after the transmitter is switched off. A more confident excitation and increased intensity of the irregularities were also confirmed when the beam was inclined south of the magnetic-zenith direction. When the ionosphere is affected by high-power HF radio emission, electron-density irregularities with sizes from tens of centimeters to tens of kilometers are formed in the region of its reflection [1]. Diagnosis of the large-scale (more than 0.5 km) structure of the ionospheric region disturbed by a high-power radio wave was based on raying the ionosphere by decametric radio emission from space radio sources, aspect scattering of HF and UHF radio waves, raying the heated region by UHF signals of low-orbit and geostationary satellites, satellite radio tomography, and electron density in-situ measurements during the flyby of spacecraft and geophysical rockets through and over the heated region (see [1, 2] and the references cited therein). Large-scale irregularities with scales 5–50 km can also be effectively studied using dual-frequency raying by signals of the Navstar (GPS) or GLONASS microwave satellite systems. During propagation through the heated region, such signals acquire an additional phase increment stipulated by the dispersion of radio waves in the ionospheric plasma and linearly related to the total electron content (TEC) on the propagation trajectory [3, 4]. Since the early eighties, this method has been used to determine the TEC in the ionosphere under natural conditions, and since 2007 the Navstar satellites have intensely been used to determine the total electron content in the ionosphere during the experiments on ionosphere modification by high-power HF radio emission. Such studies were based on the HAARP [5] and Sura [2, 6] facilities. A TEC increase correlated with the ionospheric heating was observed in the daytime experiments [2] and [5]. In [6], where the observations were performed mainly after the sunset with the beam of the Sura facility inclined 12 ◦ south in the geomagnetic meridian plane, both a notable TEC increase in the heated region determined by the angular sizes of the antenna pattern and long-period (10–15 min) TEC variations relative to the average value were recorded. On the basis of obtained results, the authors of [6] made a statement about the manifestation of the magnetic-zenith effect as the most effective impact on the ionosphere in the direction along the geomagnetic field.

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.

Controlled injection of high-power radio pulses into the ionosphere-magnetosphere system and appearance of microsubstorms on October 2, 2007

Insignificant geomagnetic disturbances, which originated during the experimental injection of high-power radio pulses into the magnetosphere-ionosphere system with the help of an HF transmitter of the Sura heating facility, are considered. The experiment was performed at 1840–1900 UT on October 2, 2007 (∼2100 MLT) at geomagnetic latitudes close to the zone of generation of the current wedge westward branch, responsible for geomagnetic substorms. The series of two magnetic microsubstorms, with a sudden initial pulse and an insignificant delay relative to the facility switching, was observed at 1840–2000 UT. A disturbance was registered at many stations in the Northern Hemisphere as a global event. The equivalent ionospheric current system of an initial pulse was similar to such a system of the westward auroral surge and had an intensity maximum at Karpogory magnetic observatory, which is the closest station to the Sura facility. Under the conditions of a quiet solar wind and low planetary geomagnetic activity, the AE auroral index correlated with the interplanetary medium parameters (the correlation coefficient reached 0.65) at 1710–2000 UT. It has been confirmed that an initial geomagnetic pulse is generated as a result of radiowave injection. The arguments for and against the generation of microsubstorms due to stimulated precipitation of magnetospheric electrons, as well as the assumption that the geoeffective impact of the interplanetary medium is intensified during the injection of high-power radiowaves near the zone where the westward branch of the current wedge of magnetospheric substorms is generated, are considered.

On the location and structure of the artificial 630-nm airglow patch over Sura facility

Abstract. Results are presented of the artificial optical emission of the atomic oxygen red line (the radiation of level O(1D) with a wavelength of 630 nm) from the HF-pumped ionosphere, obtained in September 2004 at the SURA heating facility situated near Nizhny Novgorod, Russia. For vertical pumping the airglow patch was increasingly displaced to the north, up to 7–8°, with increasing reflection altitude. For large brightness of the emission, the airglow patch started to develop at the northern edge of the pump beam and later expanded to the south. These effects are attributed to the precipitation of supra-thermal electrons from the pump wave upper hybrid resonance altitude to lower altitudes where excitation of the O(1D) level is more effective due to the larger density of atomic oxygen, and the O(1D) lifetime is shorter. For a pump beam inclination of 12° to the south, the optical spot was displaced by 4–5° to the south relative to the straight-line projection of the pump beam onto the sky. This exceeds that expected from the ray tracing and may be related, most probably, to the so-called "magnetic zenith" effect. In addition, mid-scale (1–10 km) magnetic field-aligned structures were observed in the pumped volume of the ionosphere. The east-west motions of the airglow patches are also analyzed.

On the morphology of Stimulated Electromagnetic Emission spectra in a wide pump wave frequency range

Results of systematic study of Stimulated Electromagnetic Emission (SEE) steady state spectrum dependence on the pump wave frequency f 0 are presented. Investigations of the HF-pumped ionosphere were performed at the SURA facility for the frequency range 4.3 < f 0 < 9.5 MHz with stepping of 1–50 kHz including the vicinities of the electron gyroharmonics nf ce from n = 4 to 7. The results are based on the data collected during 1996–2004. The main tendencies in a behavior of the most prominent SEE spectral features (their peak and total intensities, and positions in the spectrum) versus f 0 are established and studied in detail. A comparative analysis of peculiarities of different spectral features allows to improve a determination of the electron gyrofrequency in the ionosphere from the SEE spectra, as well as provides a base for deeper understanding nonlinear processes in the pump-driven upper hybrid turbulence responsible for the SEE generation.

Electron-Density Distribution in the Upper Ionosphere under Conditions of a Mid-Latitude F-Spread

We present the results of the last experiments aimed at studying the phenomenon of mid-latitude F-spread by radio-raying of the ionosphere using the signal from the SURA facility received onboard the NASA spacecraft WIND. A generalized model of spatio-temporal distribution of the electron density in the mid-latitude ionosphere under F-spread conditions is proposed. Based on this model describing large-scale ionospheric irregularities, we calculate the ray trajectories of HF radio waves. We also discuss the known results of comparative measurements of the variances of relative electron-density fluctuations in large-scale irregularities of the mid-latitude ionosphere, carried out by the OGO-6 spacecraft, and the frequency broadening of the ionograms of ground-based stations for the vertical sounding. It is shown that the proposed model of electron-density disturbances in the mid-latitude ionosphere in the presence of F-spread is able not only to describe well the main qualitative feature of HF radiowave propagation under disturbed geophysical conditions, but also to reproduce quite accurately the quantitative parameters of the frequency broadening of reflected HF signals under conditions of standard and developed F-spread.