High-power HF Radio Waves Research Articles

Determination of the vector velocity of artificial ionospheric irregularities based on Doppler measurements by the bi-static scatter method of HF radio signals propagating over long radio paths

During experiments on the modification of the high-latitude ionosphere by high-power HF radio waves of ordinary or extraordinary polarization of the EISCAT/Heating facility (Tromsø, Norway) in 2013, 2016, and 2019, Doppler measurements of diagnostic HF radio signals over long radio paths were carried out by the bistatic scatter method. We studied characteristics of Doppler frequency variations in bistatic scattered radio signals, using the experimental results obtained along radio paths of different lengths (up to ~8500 km) and orientation. We examined numerical dependences of the Doppler frequency variations in a radio signal on the azimuth of the wave vector of a radio wave incident onto an artificially disturbed region, on the bistatic scattering angle, and on the azimuthal direction of irregularity motion in an artificially disturbed region of the ionosphere. From simultaneous measurements of the Doppler frequency fD of the radio signal along two diagnostic radio paths, we numerically estimated the velocity vector of irregularities in the artificially disturbed region of the ionosphere. The total vector velocity of artificial ionospheric irregularities can be calculated from measurements of the Doppler frequency shift along several long diagnostic radio paths after preliminary analysis of experimental observations with the results of trajectory modeling of diagnostic HF radio signals.

Определение вектора скорости искусственных ионосферных неоднородностей по данным доплеровских измерений методом ракурсного рассеяния КВ радиосигналов, распространяющихся на протяженных радиотрассах

During experiments on the modification of the high-latitude ionosphere by high-power HF radio waves of ordinary or extraordinary polarization of the EISCAT/Heating facility (Tromsø, Norway) in 2013, 2016, and 2019, Doppler measurements of diagnostic HF radio signals over long radio paths were carried out by the bistatic scatter method. We studied characteristics of Doppler frequency variations in bistatic scattered radio signals, using the experimental results obtained along radio paths of different lengths (up to ~8500 km) and orientation. We examined numerical dependences of the Doppler frequency variations in a radio signal on the azimuth of the wave vector of a radio wave incident onto an artificially disturbed region, on the bistatic scattering angle, and on the azimuthal direction of irregularity motion in an artificially disturbed region of the ionosphere. From simultaneous measurements of the Doppler frequency fD of the radio signal along two diagnostic radio paths, we numerically estimated the velocity vector of irregularities in the artificially disturbed region of the ionosphere. The total vector velocity of artificial ionospheric irregularities can be calculated from measurements of the Doppler frequency shift along several long diagnostic radio paths after preliminary analysis of experimental observations with the results of trajectory modeling of diagnostic HF radio signals.

Comment on Blagoveshchenskaya et al. Artificial Ducts Created via High-Power HF Radio Waves at EISCAT. Remote Sens. 2023, 15, 2300

The claim that incoherent scatter radar data show electron density enhancements of 50–80% during some ionospheric heating experiments in a recent paper is questioned. The backscatter from the monostatic radar can indeed be enhanced during these experiments, but the conclusion that a large electron density increase is the cause is almost certainly wrong. Some natural plasma line data are presented in support of our claim. Previously published studies of similar events and a possible explanation for the observed increases in backscattered power are pointed out.

Artificial Ducts Created via High-Power HF Radio Waves at EISCAT

Ducts (field-aligned plasma density enhancements) provide a link into the magnetosphere and can guide whistler waves. Inside ducts, wave-particle interactions occur efficiently; therefore, their presence contributes to the removal of energetic particles from the magnetosphere. We present experimental results concerning the characteristics, behavior, and excitation thresholds of ducts induced by extraordinary (X-mode) polarized high-power HF radio waves emitted towards the magnetic zenith (MZ) into the upper ionosphere at EISCAT (European Incoherent SCATter). The features and behavior of ducts were diagnosed by the EISCAT incoherent scatter radar (ISR) at Tromsø and the CUTLASS (SuperDARN) Finland radar at Hankasalmi. The state of the ionosphere was monitored by the Dynasonde in Tromsø. It was found that the electron density Ne enhancements inside ducts were of 50–80% above the background Ne values and their transverse size (normal to the magnetic flux tube) corresponded to about 3–4° in the north–south direction. They were generated during magnetically quiet periods and extended from ~300 to 320 km up to the upper altitude limit of the EISCAT radar measurements (600–700 km), when heater frequencies were both below and above the critical frequency of the F2 layer (fH ≤ foF2 and fH > foF2), regardless of whether HF-induced plasma and ion lines were generated or not. Comparing the O-/X-mode effects from the EISCAT radar observations, it was shown that the creation of the strong Ne ducts is a typical characteristic of the X-mode pulses. As a rule, electron density enhancements were not observed during O-mode pulses. A plausible mechanism for the creation of X-mode artificial ducts is discussed.

Реакция профиля электронной концентрации ионосферы на воздействие мощного КВ-радиоизлучения

Using electron density and temperature equations, we have modeled the dynamics of the electron density profile in the ionosphere due to the expulsion of plasma from localization regions of plasma waves, pumped by high-power HF radio waves, i.e. wave reflection and upper hybrid resonance regions. Causes of the ionospheric plasma expulsion are an increase in the gas-kinetic pressure due to the ohm heating of electrons by plasma waves, and the high-frequency pressure of plasma waves (ponderomotive expulsion). We have established that the ponderomotive expulsion develops more rapidly and is responsible for the formation of local regions of plasma density depletion near plasma resonances, whereas the gas-kinetic pressure increase is responsible for the formation of lower-density region, which is slower in time and more extended and smoother in height. The results obtained qualitatively agree with the data from the experiment conducted at the HAARP facility in 2014.

Response of ionospheric electron density profile to the action of powerful HF radio-wave radiation

Using electron density and temperature equations, we have modeled the dynamics of the electron density profile in the ionosphere due to the expulsion of plasma from localization regions of plasma waves, pumped by high-power HF radio waves, i.e. wave reflection and upper hybrid resonance regions. Causes of the ionospheric plasma expulsion are an increase in the gas-kinetic pressure due to the ohm heating of electrons by plasma waves, and the high-frequency pressure of plasma waves (ponderomotive expulsion). We have established that the ponderomotive expulsion develops more rapidly and is responsible for the formation of local regions of plasma density depletion near plasma resonances, whereas the gas-kinetic pressure increase is responsible for the formation of lower-density region, which is slower in time and more extended and smoother in height. The results obtained qualitatively agree with the data from the experiment conducted at the HAARP facility in 2014.

Joule heating in the mid-latitude ionosphere by high power HF radio waves

We present an estimation of the heating rate due to Joule heating in the F region of the ionosphere as a result of its interaction with high-power HF O-mode radio waves transmitted by a ground-based antenna. We refer to experiments conducted at Platteville, Colorado in the 70’s, i.e., at a mid-latitude ionosphere, as the ionospheric conditions and experimental facility parameters are well known. Analytical expressions for the electric field of the HF wave, ionospheric electric conductivity and heating rate are inserted into the calculations. The subsequent spatial and temporal changes in electron and ion temperatures were estimated. The results show that the electron temperatures demonstrate an increase of 115% above their unperturbed values and the ion temperatures demonstrate a corresponding increase of 13%.

Satellite Measurements of Plasma Disturbances and Electric Currents Induced in the Midlatitude Ionosphere Modified by High-Power HF Radio Waves

Satellite Measurements of Plasma Disturbances and Electric Currents Induced in the Midlatitude Ionosphere Modified by High-Power HF Radio Waves

Excitation of Langmuir and Ion–Acoustic Turbulence in the High-Latitude Ionosphere by a High-Power HF Radio Wave Simultaneously Below and Above the F2-Layer Maximum

We present the results of experimental studies of the generation peculiarities and features of the Langmuir and ion–acoustic turbulence in the F region of the high-latitude ionosphere excited by high-power HF O-mode radio waves emitted by the EISCAT/Heating facility (Tromso, Norway) in the direction of the Earth’s magnetic field. The experiment was carried out at frequencies fH close to the fourth gyroharmonic, fH < 4fce, and the cutoff frequency of the F2 layer, foF2 , fH < foF2 < fH+fce/2, where fce is the electron gyrofrequency. By using the EISCAT incoherent scatter radar (930 MHz), a joint analysis of the plasma and ion line spectra simultaneously below and above the F2-layer maximum was performed. The excitation of the HF-induced plasma lines outshifted by 0.35–0.45 MHz from the pump-wave frequency and HF-enhanced ion lines simultaneously below and above the F2-layer maximum was found for the first time. The mechanisms of the pump-wave propagation to altitudes above the F2-layer maximum and a plausible mechanism for the excitation of the instability responsible for the generation of HF-enhanced ion lines and HF-induced plasma lines above the F2-layer maximum are discussed.

Radio Emission of Rydberg Atoms in the Upper Atmosphere Modified by High-Power HF Radio Waves

We report on the results of studying the radio emission of the Rydberg states of atoms and molecules in the Earth’s upper atmosphere at ionospheric altitudes when the ionosphere is modified by high-power HF radio waves radiated by the Sura heating facility. Radio emission from the upper atmosphere, caused by the emission of highly excited Rydberg atoms and molecules with the principal quantum number n = 163–169 and n = 225 (decimeter wavelength range) and two spectral features that coincide with the frequencies of transitions between Rydberg states m = 169 → n = 168 with the transition frequency νn = 1375.35 MHz and m = 166 → n = 165 with νn = 1451.5 MHz were detected. Characteristic altitudes of the Rydberg radiation generation region were 150–250 km. The radio emission intensity corresponds to 10–45 K, which is comparable with the intensity of the radio emission generated during solar flares.

Total Electron Content Measurements in the Ionosphere Disturbed by High-Power High-Frequency Waves by the Methods of Incoherent Scattering of Radio Waves and Radio Sounding by Glonass Satellite Signal

We present the results of comparing the total electron content measurements based on GLONASS satellite signals and the EISCAT UHF incoherent scatter radar (Tromso, Norway) during modification of the high-latitude ionosphere in the magnetic zenith direction by high-frequency radio waves of the EISCAT/Heating facility (Tromso, Norway). The measurements were performed during two experiment campaigns in October 2013 and in October 2018. In general, the total electron content variations obtained from the radar data in the altitude range 100–400 km were consistent with the total electron content variations from the GLONASS satellites. The efficiency of using GLONASS satellites for observations of high-latitude phenomena was shown. The anomalous increase in the total electron content by 4 TECU obtained from the incoherent scatter radar when the ionosphere was heated in the region close to the magnetic zenith is considered. The GLONASS satellite data show the total electron content reduction in the same region. To explain the disagreement between measurements by these two methods, the effect of smallscale electron-density irregularities arising in the region modified by high-power HF radio waves is considered. It is shown that when the electron density in artificial irregularities exceeds the background density of the medium by 2 ・ 10−3 times in relative units, scattering by irregularities with spatial scales of the order of 16 cm becomes predominant in the reflected signal.

Precipitation of Energetic Electrons from the Earth’s Radiation Belt Stimulated by High-Power HF Radio Waves for Modification of the Midlatitude Ionosphere

Based on the results of the experiments performed in 2005–2010 within the framework of the Sura—DEMETER program, we analyze the features of the precipitations of energetic electrons (with energies E ≈ 100 keV) from the Earth’s radiation belt. The modification of the ionospheric F2 region was conducted by means of high-power HF O-mode radio waves radiated in the CW regime. The precipitations were detected using the equipment onboard DEMETER, a French microsatellite. The conditions of precipitation appearance were determined, and it was found that the electron precipitation region was stretched along the geomagnetic meridian to a distance of 1300 km; the size of the region in the transverse direction is about 400 km. It was shown by ionosonde measurements that such precipitations lead to increased absorption of radio waves in the lower ionosphere. It is assumed that the mechanism for precipitation of electrons from the Earth’s radiation belt is determined by the interaction of energetic electrons with VLF radio waves, which are generated due to the interaction of the amplitude-unmodulated O-mode pump wave with the ionospheric plasma near the wave reflection height.

Characteristics of the Plasma Disturbance Excited at Altitudes of 450–500 km During the “Sura” Facility Operation

We discuss the results of measuring characteristics of the artificial plasma disturbances excited at altitudes of 450–500 km with the ionospheric F2 layer modified by high-power HF radio waves from the Sura facility. It is found that at these altitudes there are plasma temperature and density variations in the HF-perturbed magnetic flux tube. No ducts with increased plasma density that were previously observed at altitudes of about 660 km were detected. The results of the studies are compared with the data from the DEMETER satellite and the results of radiotomographic measurements. It is noted that the field-aligned currents induced in a perturbed ionosphere during the Sura operation were detected for the first time using SWARM satellites.

On Spatial Structuring of the F2 Layer Studied by the Satellite Radio Sounding of the Ionosphere Disturbed by High-Power HF Radio Waves

We present the results of studying the characteristics of the artificial plasma structures excited in the ionospheric F2 region modified by high-power HF radio waves. The experiments were carried out at the Sura heating facility using satellite radio sounding of the ionosphere. The plasma density profile was reconstructed with the highest possible spatial resolution for today, about 4 km. In a direction close to the magnetic zenith of the pump wave, the following phenomena were observed: the formation of a cavity with a 15% lower plasma density at the altitudes of the F2 layer and below; the formation of an area with plasma density increased by 12% at altitudes greater than 400 km. With a long-term quasiperiodic impact of the pump wave on the ionosphere, wavy large-scale electron-density perturbations (the meridional scale λx ≈ 130 km and the vertical scale λz ≈ 440 km) are also formed above the Sura facility. These perturbations can be due to the plasma density modulation by an artificial acoustic-gravity wave with a period of 10.6 m, which was formed by the heat source inside a large-scale cavity with low plasma density; there is generation of the electron density irregularities for the electrons with ΔNe/Ne ≈ 3% in the form of layers having the sizes 10–12 km along and about 24 km across the geomagnetic field, which are found both below and above the F2-layer maximum. The mechanisms of the formation of these plasma structures are discussed.

The Results of Measurements of Features of Artificial Electromagnetic and Plasma Perturbations in the Outer Ionosphere of the Earth Using the DEMETER Satellite

The results of the DEMETER satellite mission for 2005–2010 are summarized. The characteristics of electromagnetic and plasma perturbations induced in the F2 layer of the Earth’s ionosphere by the highpower HF radio waves from the SURA heating facility are analyzed.

Features of the Ionospheric Artificial Airglow Caused by Ohmic Heating and Plasma Turbulence-Accelerated Electrons Induced by HF Pumping of the Sura Heating Facility

We present the results of studying the ionospheric F2 region airglow in the atomic-oxygen red line (λ = 6300Ǻ) when the ionosphere is pumped by high-power HF radio waves. Either thermal modulation of the background airglow brightness or, simultaneously with it, the red-line intensity enhancement were observed, depending on the ionospheric and plasma-wave parameters. Analysis of the red-line emission behavior makes it possible to separate the influence of the ohmic heating and acceleration of electrons by plasma turbulence on the airglow features.

Generation of the Super Small-Scale Artificial Ionospheric Irregularities in the Ionosphere Pumped by High-Power HF Radio Waves

We present the results of experimental studies of generation of super small-scale plasma-density irregularities in the ionospheric F2 region pumped by a high-power HF O-mode wave at frequencies close to the fourth gyroharmonic in the region of its interaction with the plasma. The experiments were performed using the Sura heating facility. The super small-scale irregularities were sounded by GPS satellite signals. It has been shown that super small-scale irregularities are excited with the most efficiency in the region of the magnetic zenith for the pump wave. The intensity of such irregularities and typical times of their development and decay are determined.

Excitation of Artificial Ionospheric Turbulence in the High-Latitude Ionospheric F Region as a Function of the Eiscat/Heating Effective Radiated Power

We present the results of experimental studies of the parameters of HF-enhanced ion–acoustic and Langmuir plasma waves, as well as small-scale artificial field-aligned irregularities (AFAIs) when the EISCAT/Heating effective radiated power is varied from 10 to 560 MW. In the course of the experiments, a high-power HF radio wave with the alternating ordinary (O-mode) and extraordinary (X-mode) polarizations was radiated towards the magnetic zenith at a frequency of 7.953 MHz lying below the cutoff frequency of the F2 layer. A fundamental difference in the development of artificial ion–acoustic and Langmuir turbulence, which is seen as HF-enhanced ion and plasma lines in the EISCAT spectra, under the O- and X-mode HF pumping was found. The minimum values of the HF pump-wave electric fields in the ionosphere when the HF-enhanced ion and plasma lines, as well as small-scale artificial field-aligned irregularities, start to be excited, were determined from experimental data both for the O- and X-mode HF pumping. Comparison between the experimental and theoretical threshold values of the electric field required for the excitation of artificial ionospheric turbulence in thermal, Langmuir, and ion–acoustic modes in the high-latitude ionospheric F2 layer for the O-mode HF pump wave was made.

On Features of the Generation of Artificial Ionospheric Irregularities with Transverse Scales of 50–200 m

We consider the features of generation of artificial ionospheric irregularities with transverse (to the geomagnetic field) scales l⊥ ≈ 50–200 m in the ionosphere modified by high-power HF radio waves. It was found that there are at least two mechanisms for generation of these irregularities in the ionospheric F region. The first mechanism is related to the resonant interaction between radio waves and the ionospheric plasma, while the second one takes place even in the absence of the resonant interaction. Different polarization of the high-power radiation was used to separate the mechanisms in the measurements.

Frequency correlation of probe waves backscattered from small scale ionospheric irregularities generated by high power HF radio waves

Aspect sensitive scattering of multi-frequency probe signals by artificial, magnetic field aligned density irregularities (with transverse size ∼1–10 m) generated in the ionosphere by powerful radio waves is considered. Fluctuations of received signals depending on stochastic properties of the irregularities are calculated. It is shown that in the case of HF probe waves two mechanisms may contribute to the scattered signal fluctuations. The first one is due to the propagation of probe waves in the ionospheric plasma as in a randomly inhomogeneous medium. The second one lies in non-stationary stochastic behavior of irregularities which satisfy the Bragg conditions for the scattering geometry and therefore constitute centers of scattering. In the probe wave frequency band of the order of 10–100 MHz the second mechanism dominates which delivers opportunity to recover some properties of artificial irregularities from received signals. Correlation function of backscattered probe waves with close frequencies is calculated, and it is shown that detailed spatial distribution of irregularities along the scattering vector can be found experimentally from observations of this correlation function.