Frequency Active Auroral Research Program Research Articles

Study of the Mesosphere and Lower Thermosphere by the Method of Creating Artificial Periodic Irregularities of the Ionospheric Plasma

This article presented a brief review of studies of the Earth’s ionosphere at the heights of the mesosphere and lower thermosphere by a method based on the creation of artificial periodic inhomogeneities (APIs) of the ionospheric plasma by high-frequency radiation from powerful thermal installations. APIs are created by a standing wave due to the interference between upward-propagating radio waves and those reflected from the ionosphere. API studies of the ionosphere were based on Bragg scattering of probing impulse signals from an artificial periodic structure. The method makes it possible to measure the parameters of the neutral and ionized components of the Earth’s atmosphere. Note that, despite the fact that the API method assumes an artificial perturbation of the ionospheric plasma, the parameters of the mesosphere and lower thermosphere are determined at the stage of inhomogeneity relaxation and characterize the undisturbed medium. To date, periodic inhomogeneities have been observed at the heating points of Zimenki and Sura ionospheric heating facility (SURA, Vasilsursk, Russia), Gissar (Tajikistan), Arecibo (Puerto Rico, USA), High Power Auroral Stimulation Observatory (HIPAS) and High Frequency Active Auroral Research Program (HAARP, Gakona, AK, USA), and European Incoherent Scatter (EISCAT, Tromso, Norway). Most of the API studies of the ionosphere were carried out at the SURA mid-latitude heating facility (56.1° N; 46.1° E). The review presented the main results of determining the parameters of the ionosphere and neutral atmosphere at altitudes of 60–120 km and studies of the atmosphere during sunrise and sunset events and solar eclipses. In fact, the review is far from a complete illustration of the possibilities of using the API method to study the mesosphere and lower thermosphere.

Geomagnetic field impacts on second harmonic generation during high power radio wave-ionosphere interaction

Contained herein are results from an experimental study of geomagnetic field (B0) impacts on second harmonic generation (SHG) during the interaction of high power, high frequency radio waves with the ionosphere. These magnetic field effects on SHG are assessed by (1) considering the proximity of the pump frequency to the electron gyroharmonic frequency and (2) considering the pump antenna beam angle relative to the geomagnetic field direction. The observations show evidence of ion Bernstein mode wave-mixing processes in stimulated electromagnetic emissions (SEEs) simultaneously near the pump wave frequency (f0) and its second harmonic (2f0). In an experiment performed at the High Frequency Active Auroral Research Program (HAARP) facility, the transmit antenna beam was either oriented along or tilted away from B0, and f0 was stepped near the second harmonic of the electron gyrofrequency (2fce). SEEs ordered by the oxygen ion gyrofrequency (fci) are observed in spectra near 2f0 for: (1) a B0-oriented antenna beam when f0≈2fce and (2) f0<2fce, when the beam is tilted away, but not beyond a maximum angle from B0. The observations motivate further studies to develop SHG into important diagnostics for the modified ionosphere.

Ionospheric HF Heating Experiment With Frequency Ramping‐up Sweep: Approach for Artificial Ionization Layer Generation

AbstractAn ionospheric high‐frequency (HF) heating experiment was conducted at the HAARP facility in Alaska by sweeping the heater frequency, near the third electron gyroharmonic, over a 145 kHz range with 4 min duration. A 446 MHz diagnostic radar was used to detect scattering from HF‐enhanced plasma waves corresponding to the HF‐enhanced ion lines (HFILs). Increasing frequency progressively moves the third gyroharmonic resonance layer downward, and this is evident in observations of both downgoing and upgoing HFILs dropping in height about 50 km. Artificial ionization was formed by the HF‐plasma interaction during this process and driven downward to about 150–155 km. Total electron content measurements oblique across the High Frequency Active Auroral Research Program transmit beam, above the altitude of primary ionization production, show variations that correspond to ionization production at lower heights. A theoretical interpretation of the experimental observations is presented to understand the HF‐plasma interaction process. It is shown that the double resonance condition enhances the excitation of the upper‐hybrid parametric decay instability (PDI). HF heater frequency ramping‐up sweep increases the spatial height span of the upper‐hybrid PDI generation region and the spectral width of generated upper‐hybrid waves, as well as provides a positive tuning frequency on the excited upper‐hybrid waves that keeps the continuous positive feedback on the Doppler‐shifted cyclotron harmonic resonance interaction. Resonant electrons gain energy from the upper‐hybrid waves and are generated in an extended spatial region; after a drift space, spatially distributed energetic electrons bunch together to build up a density structure.

Simulation studies of strongly turbulent stimulated Brillouin backscattering during ionospheric heating

ABSTRACTRecent experimental observations of stimulated electromagnetic emissions (SEE) during ionospheric heating have shown that the SEE spectrum produced as a result of the stimulated Brillouin backscatter (SBS) instability is structurally very different for low and high pump power regimes. Initial results from electromagnetic Particle-In-Cell (PIC) simulation studies conducted to investigate the difference in the SBS SEE spectrum for the two pump power regimes are presented. Simulation results presented here are used to gain insight into ionospheric heating experiments at the High Frequency Active Auroral Research Program (HAARP) facility in which the pump power either linearly increased from a low power to the maximum available power, or was maintained at the maximum available power during the heating cycle. The observations show (1) a distinct, narrow SEE spectral line downshifted from the pump frequency, due to SBS, for the low power case and (2) a broad, aggregate SBS SEE structure downshifted from the pump frequency for the high power heating. In general, the spectra of the backscattered EM field obtained from PIC simulations for the two pump power regimes show correspondence with the HAARP observational data. Simulations predict that the broad spectral structure for the high power case results from strong ion acoustic (IA) turbulence. Further characteristics of the strong turbulence include cavity development in the ion density in which (I) strong long lifespan EM waves are trapped (II) short-lived ES waves are trapped, and (III) high temperature electrons exist.

Pump Power Effects on Second Harmonic Stimulated Electromagnetic Emissions During Ionosphere Heating

AbstractDue to the potential for new diagnostic capabilities, there has been renewed interest in the generation of ionospheric stimulated electromagnetic emissions (SEEs) near the second harmonic of the pump frequency (ω0), a process known as second harmonic generation (SHG). Observations of SHG during experiments at the High Frequency Active Auroral Research Program facility in which ω0 was stepped near the third harmonic of the electron gyrofrequency, 3ωce, and the transmit power linearly increased over the heating cycle at each ω0, were reported recently. A key observation was the linkage between SEEs within ±30 Hz of ω0, due to stimulated Brillouin scatter, and within ±30 Hz of 2ω0. This current work reports further High Frequency Active Auroral Research Program observations that compare the time evolution of SEEs including SHG under the following two transmit power conditions (I) linear power ramp (II) maximum available power (2.8 MW). During these experiments, ω0 was stepped near 3ωce and also 2ωce. The results show that SEEs within ±100 Hz of ω0 and 2ω0 are both suppressed within a few seconds when the ionosphere is irradiated with the maximum available power. These SEEs appear to be suppressed before the onset of field‐aligned irregularities at the upper hybrid layer which is not in line with previous reports. Thus, other mechanisms, which are discussed, could possibly be responsible for the observed suppression of stimulated Brillouin scatter and SHG. Some preliminary diagnostics are derived from the SHG spectra temporal evolution by leveraging concepts from the field of laser plasma interactions.

NSEE Yielding Electron Temperature Measurements at the Arecibo Observatory

AbstractNarrowband stimulated electromagnetic emissions (NSEE), a component of radio emissions created during high‐frequency (HF) radiowave ionospheric modification experiments, occur within 1 kHz of the HF pump frequency. NSEE was observed and studied for the first time at the HAARP (High Frequency Active Auroral Research Program) facility in Alaska (Norin et al., 2009, https://doi.org/10.1103/PhysRevLett.102.065003; Bernhardt et al., 2010, https://doi.org/10.1103/PhysRevLett.104.165004). Magnetized stimulated Brillouin scatter (MSBS) is a component of NSEE, which was also first observed at HAARP (Norin et al., 2009, https://doi.org/10.1103/PhysRevLett.102.065003; Bernhardt et al., 2010, https://doi.org/10.1103/PhysRevLett.104.165004) and later at European Incoherent Scatter Scientific Association (Fu et al., 2015, https://doi.org/10.5194/angeo-33-983-2015). Ion‐acoustic and electrostatic ion cyclotron modes are the daughter products of MSBS and can be used for the determination of the electron temperature and of the presence of minor ion species, respectively, in the HF‐modified ionosphere. Here we present the first observations of the MSBS process at magnetic midlatitudes, excited during radio wave ionospheric modification experiments at the Arecibo Observatory. The NSEE observations, in combination with a theoretical model and the wave matching conditions, are used to estimate background ionospheric parameters. A qualitative comparison of the MSBS component of the NSEE spectrum with the thermal ion line measured by incoherent scatter radar is presented.

Artificial Aurora Produced by HAARP

AbstractWe present results from the ionospheric heating experiment conducted at the High Frequency Active Auroral Research Program (HAARP) facility, Alaska, on 12 March 2013. During the experiment, HAARP transmitted in the direction of the magnetic zenith X‐mode 4.57‐MHz wave. The transmitted power was modulated with the frequency of 0.9 mHz, and it was pointed on a 20‐km spot at the altitude of 120 km. The heating (1) generates disturbances in the magnetic field detected with the fluxgate magnetometer on the ground and (2) produces bright luminous spots in the ionosphere, observed with the HAARP telescope. Numerical simulations of the 3‐D reduced magnetohydrodynamic (MHD) model reveal that these effects can be related to the magnetic field‐aligned currents, excited in the ionosphere by changing the conductivity in the E region when the large‐scale electric field exists in the heating region.

Review of Controlled Excitation of Non-linear Wave-Particle Interactions in the Magnetosphere

Controlled experiments involving injection of 0.5 Hz – 8 kHz electromagnetic waves into the Earth’s magnetosphere have played an important role in discovering and elucidating wave-particle interactions in near-Earth space. Due to the significant engineering challenges of efficiently radiating in the ELF/VLF: 300 Hz – 30 kHz band, few experiments have been able to provide sustained transmissions of sufficient power to excite observable effects for scientific studies. Two noteworthy facilities that were successful in generating a large database of pioneering and repeatable observations were the Siple Station Transmitter in Antarctica and the High Frequency Active Auroral Research Program (HAARP) facility in Alaska. Both facilities were able to excite Doppler shifted cyclotron resonance interactions leading to linear and nonlinear wave amplification, triggering of free running emissions, and pitch angle scattering of energetic electrons. Amplified and triggered waves were primarily observed on the ground in the geomagnetic conjugate region after traversal of the magnetosphere along geomagnetic field aligned propagation paths or in the vicinity of the transmitter following two traversals of the magnetosphere. In several cases, spacecraft observations of the amplified and triggered signals were also made. The observations show the amplifying wave particle interaction to be dynamically sensitive to specific frequency and also specific frequency-time format of the transmitted wave. Transmission of multiple coherent waves closely spaced in frequency showed that the wave particle interaction requires a minimum level of coherency to enter the nonlinear regime. Theory and numerical simulations point to cyclotron resonance with counter streaming particles in the 10-100 keV range as the dominant process. A key feature of the nonlinear interaction is the phase-trapping of resonant particles by the wave that is believed to drive non-linear wave amplification and the triggering of free-running emissions. Observations and modeling of controlled wave injections have important implications for naturally occurring whistler mode emissions of hiss and chorus and the broader phenomena of radiation belt dynamics. A review of observational, theoretical, and numerical results is presented and suggestions for future studies are made.

Asymmetry in Stimulated Emission Polarization and Irregularity Evolution During Ionospheric Electron Gyroharmonic Heating

AbstractThe first report is made of a holistic investigation of stimulated electromagnetic emission (SEE) during ionospheric electron gyroharmonic heating using a diagnostic approach at the High Frequency Active Auroral Research Program facility. The evolution of SEE polarization and plasma irregularity development near the third electron gyroharmonic 3fce is investigated, which provides new insights into SEE generation mechanisms by the associated parametric decay instabilities. New more complex SEE spectral line behavior is clearly observed for varying transmitter beam angles. New SEE spectral emissions are observed at ∼75 kHz when pumping below 3fce. The high‐frequency radar echoes and SEE polarimetry appear asymmetric for pumping above 3fce, which implies that the broad upshifted maximum spectral line formation involves plasma irregularities scattered by high‐frequency radar echoes. This has important implications for understanding artificial ionization layer generation during ionospheric modification.

First Observations of Narrowband Stimulated Electromagnetic Emissions at the Pump Frequency Second Harmonic During Ionosphere Interaction Experiments

AbstractReported herein are first observations of narrowband stimulated electromagnetic emissions (NSEEs) within ±30 Hz of the second harmonic of the pump wave frequency during ionospheric heating experiments at the High Frequency Active Auroral Research Program facility. The observations are juxtaposed with contemporaneous NSEEs observed within ±30 Hz of the pump wave frequency. The transmit power of the pump wave is linearly increased, and the pump wave frequency is stepped through frequencies near the third electron gyroharmonic frequency during the experiment. The first observation is that there is a transmit power threshold for the occurrence of NSEEs downshifted from the second harmonic of the pump wave frequency. Secondly, when downshifted NSEEs are present at both the pump frequency and its second harmonic, the transmit power threshold for the onset of both are comparable. Third, the frequency offset of the downshifted NSEEs spectral line from the second harmonic frequency is approximately twice the frequency offset of the downshifted NSEEs spectral line from the pump wave frequency when the downshifted NSEEs are present near both the pump and second harmonic frequency. Finally, the NSEEs at the second harmonic of the pump wave frequency are suppressed at pump frequencies very close to the third electron gyroharmonic frequency.

Artificial Ionospheric GPS Phase Scintillation Excited During High‐Power Radiowave Modulation of the Ionosphere

AbstractArtificial ionospheric GPS phase scintillation effects excited during the fourth gyroharmonic (4fce) heating at the High Frequency Active Auroral Research Program along with a theoretical model for the associated ionospheric irregularities are presented in this paper. The generation mechanism and time evolution of artificial GPS phase scintillation have been investigated using the simultaneous collected data including GPS scintillation, wideband stimulated electromagnetic emissions (WSEE), and ionosonde. The generation of the broad upshifted maximum, a WSEE spectral line associated with super small striation, through the four‐wave decay instability is studied using a theoretical model. The possible role of decameter‐scale irregularities within the Fresnel zone as well as super small striation in the GPS phase scintillation is investigated using the correlation of WSEE features with the scintillation data. Time evolution of slant total electron content (STEC) data and modulation of GPS phase and amplitude are compared with the theoretical model to study the plasma waves involved in the scintillation process. The similarity of theoretical and previously developed computational results, with the observations, is discussed. Specifically, the time evolution of STEC fluctuations including an initial growth period and subsequent saturation has been compared with the estimated growth rate of upper hybrid and electron Bernstein waves using the theoretical calculations as well as previous computational results. The damping process associated with the decay of STEC fluctuations after the initial growth has been investigated by considering the nonlinear behavior of electron Bernstein waves obtained from the computational model.

Effects of Anthropogenic Activities on Pore Pressure of the Earth’s Crust - A Desk Review

The objective of this chapter is to identify and analyse the major anthropogenic factors affecting pore pressure of the rocks inside the Earth’s crust which determines the frequency of earthquakes and is responsible for causing seismic events, eventually leading to seismic movements. These activities include construction of dams, hydraulic fracking, carbon sequestration, and radiations from certain technologies such as the United States’ High Frequency Active Auroral Research Program (HAARP) which is now being used for research purposes. It also studies how temperature and pressure are related and trigger earthquakes and how global warming is affecting the Earth’s pore pressure. The effects of these factors were assessed on different parts of the world such as in the USA, Pakistan and India, where earthquakes were triggered. The study is based on desk research, including review of research papers and case studies on the subject. The findings from this secondary review indicated that fracking and building reservoirs have resulted in significant seismic events in many parts of the world, even in areas such as Oklahoma, USA, which were not seismically active, but which witnessed earthquakes after fracking and reservoir projects were initiated (Rubinstein and Mahani 2015). Moreover, there exists a positive correlation between temperature increase and earthquake frequency (Usman et al. 2016). Furthermore, the chapter also studies if the radiations emitted under programmes such as HAARP can cause disturbance in the earth’s crust because very low frequency radiations emitted from transmitters towards ionosphere, gets reflected back to the earth, can also trigger seismic movements in the crust (Kim et al. 2002). However, human factors such as building of artificial dams, and hydraulic fracking are also major contributing factors towards increasing the frequency of earthquakes around the globe (Petersen et al. 2016). The chapter discusses how the Sendai Framework can play a role to reduce the impacts of anthropogenic activities which can trigger disasters, such as earthquakes.

Peculiarities of VLF wave propagation in the Earth's magnetosphere in the presence of artificial large‐scale inhomogeneity

AbstractWe study specific features of VLF waves propagation in the Earth's ionosphere and magnetosphere in the presence of large‐scale field‐aligned plasma inhomogeneities (ducts). These inhomogeneities can, e.g., be formed during the ionosphere heating by high‐power HF facilities such as High Frequency Active Auroral Research Program and “Sura.” They can extend up to altitudes of several thousand kilometers along geomagnetic field lines and have transverse scales of about 1° determined by the heated region scale. We analyze ray trajectories of VLF waves with frequencies of 1 to 15 kHz starting from about 100 km altitude and use the plasma parameters obtained within the framework of the SAMI2 simulation model (Huba et al., 2000). This model employs MHD equations for thermal plasma and allows one to obtain the plasma parameters along the entire magnetic flux tube in a fixed meridional plane. By knowing the ray trajectories, we calculate and compare the amplitude variation along the ray paths for the cases of unperturbed and heated ionosphere. We show that the presence of a large‐scale density disturbance produced by the HF heating can lead to significant changes of wave propagation trajectories. In particular, efficient guiding of VLF waves in this region can take place, which in turn can result in the appearance of several wave focusing regions and a drastic local increase of the VLF wave amplitude in these regions (up to ∼10 times as compared to the case of unperturbed plasma). The number of focusing regions is determined by an extension of an artificial duct along the geomagnetic field.

The Path to a Transportable Ionospheric Heater—Tuning Methods

A tunable electrically small antenna (ESA) designed to be naturally resonant at 100 MHz is evaluated for its range of tuning and feasibility for use in a mobile ionospheric heating (MIH) setup. The overarching goal is to match the ionospheric heating performance of the 180 element array at the high frequency active auroral research program (HAARP), which occupies approximately $1.2 \times 10^{5}~\text{m}^{2}$ of land in Gakona, Alaska. While each HAARP crossed dipole element occupies 440 $\text{m}^{2}$ of land and is tunable in the range of 2.7–10 MHz using automatic matching networks, the presented ESA approach is aimed toward enabling the fabrication of a transportable MIH array platform capable of high continuous wave (cw) power, albeit with a linear dimension five to ten times smaller than that of an equivalent dipole antenna. It is elucidated that the capacitively tuned ESA is continuously tunable to a frequency about 50% lower than that of the ESA’s base frequency, albeit the resonant antenna structure carries a fractional bandwidth of merely 1%–2%.

Unique concurrent observations of whistler mode hiss, chorus, and triggered emissions

AbstractWe present a unique 2 h ground‐based observation of concurrent magnetospheric hiss, chorus, VLF triggered emissions as well as ELF/VLF signals generated locally by the High Frequency Active Auroral Research Program (HAARP) facility. Eccentricity of observed wave polarization is used as a criteria to identify magnetospheric emissions and estimate their ionospheric exit points. The observations of hiss and chorus in the unique background of coherent HAARP ELF/VLF waves and triggered emissions allow for more accurate characterization of hiss and chorus properties than in typical ground‐based observations. Eccentricity and azimuth results suggest a moving ionospheric exit point associated with a single ducted path at L ~ 5. The emissions exhibit dynamics in time suggesting an evolution of a magnetospheric source from hiss generation to chorus generation or a moving plasmapause location. We introduce a frequency band‐limited autocorrelation method to quantify the relative coherency of the emissions. A range of coherency was observed from high order of coherency in local HAARP transmissions and their echoes to lower coherency in natural chorus and hiss emissions.

Investigation of third gyro-harmonic heating at HAARP using stimulated radio emissions and the MUIR and Kodiak radars

This paper presents data from two campaigns at the High Frequency Active Auroral Research Program facility (HAARP) in 2011 and 2012. The measurements of stimulated radio emissions (often called stimulated electromagnetic emissions or SEE) were conducted 15km from the HAARP site. The potential of Narrowband SEE (NSEE) as a new diagnostic tool to monitor artificial irregularities excited during HF-pump heating of the ionosphere is the main goal of this paper. This has been investigated using well established diagnostics including the Modular UHF Ionospheric Radar (MUIR) and Kodiak SuperDARN radars as well as Wideband SEE (WSEE). The measured data using these three diagnostics were compared to characterize the ionospheric parameters and study the plasma irregularities generated in the interaction region. Variation of the wideband/narrowband SEE features, SuperDARN echoes, and HF-enhanced ion lines (EHIL) were studied with pump power variation, pump frequency stepping near the third electron gyro-frequency (3fce) as well as changing beam angle relative to the magnetic zenith. In particular, electrostatic plasma waves and associated irregularities excited near the reflection resonance layer as well as the upper-hybrid resonance layer are investigated. The time evolution and growth rate of these irregularities are studied using the experimental observations. Close alignment of narrowband SEE (NSEE) with wideband SEE (WSEE) and EHIL was observed. SuperDARN radar echoes and WSEE also showed alignment as in previous investigations. Correlations between these three measurements underscore potential diagnostics by utilizing the NSEE spectrum to estimate ionospheric parameters such as electron temperature.

Numerical study of the generation and propagation of ultralow-frequency waves by artificial ionospheric F region modulation at different latitudes

Abstract. Powerful high-frequency (HF) radio waves can be used to efficiently modify the upper-ionospheric plasmas of the F region. The pressure gradient induced by modulated electron heating at ultralow-frequency (ULF) drives a local oscillating diamagnetic ring current source perpendicular to the ambient magnetic field, which can act as an antenna radiating ULF waves. In this paper, utilizing the HF heating model and the model of ULF wave generation and propagation, we investigate the effects of both the background ionospheric profiles at different latitudes in the daytime and nighttime ionosphere and the modulation frequency on the process of the HF modulated heating and the subsequent generation and propagation of artificial ULF waves. Firstly, based on a relation among the radiation efficiency of the ring current source, the size of the spatial distribution of the modulated electron temperature and the wavelength of ULF waves, we discuss the possibility of the effects of the background ionospheric parameters and the modulation frequency. Then the numerical simulations with both models are performed to demonstrate the prediction. Six different background parameters are used in the simulation, and they are from the International Reference Ionosphere (IRI-2012) model and the neutral atmosphere model (NRLMSISE-00), including the High Frequency Active Auroral Research Program (HAARP; 62.39° N, 145.15° W), Wuhan (30.52° N, 114.32° E) and Jicamarca (11.95° S, 76.87° W) at 02:00 and 14:00 LT. A modulation frequency sweep is also used in the simulation. Finally, by analyzing the numerical results, we come to the following conclusions: in the nighttime ionosphere, the size of the spatial distribution of the modulated electron temperature and the ground magnitude of the magnetic field of ULF wave are larger, while the propagation loss due to Joule heating is smaller compared to the daytime ionosphere; the amplitude of the electron temperature oscillation decreases with latitude in the daytime ionosphere, while it increases with latitude in the nighttime ionosphere; both the electron temperature oscillation amplitude and the ground ULF wave magnitude decreases as the modulation frequency increases; when the electron temperature oscillation is fixed as input, the radiation efficiency of the ring current source is higher in the nighttime ionosphere than in the daytime ionosphere.

Exploring HF‐induced ionospheric turbulence by Doppler sounding and stimulated electromagnetic emissions at the High Frequency Active Auroral Research Program heating facility

AbstractWe report on the features of the F region plasma perturbations during HF heating experiments at the High Frequency Active Auroral Research Program facility in March–April 2011 and May–June 2014. The diagnostics included multifrequency Doppler (phase) sounding (MDS) and stimulated electromagnetic emission (SEE). The results concern modification of the electron density profile near the reflection and upper hybrid heights, as well as correlation of the density modification with temporal behavior of narrow continuum, downshifted maximum, and broad continuum SEE spectral features. We reveal also a new SEE spectral feature which appears in the SEE spectra for the pump frequency f0 near the third and fourth electron gyroharmonics. It is located in the SEE spectrum well below the pump wave frequency, f − f0 ~ −(40–220) kHz, occupies a wide frequency range till 100–150 kHz, and is termed the broad downshifted emission.

Large ionospheric disturbances produced by the HAARP HF facility

AbstractThe enormous transmitter power, fully programmable antenna array, and agile frequency generation of the High Frequency Active Auroral Research Program (HAARP) facility in Alaska have allowed the production of unprecedented disturbances in the ionosphere. Using both pencil beams and conical (or twisted) beam transmissions, artificial ionization clouds have been generated near the second, third, fourth, and sixth harmonics of the electron gyrofrequency. The conical beam has been used to sustain these clouds for up to 5 h as opposed to less than 30 min durations produced using pencil beams. The largest density plasma clouds have been produced at the highest harmonic transmissions. Satellite radio transmissions at 253 MHz from the National Research Laboratory TACSat4 communications experiment have been severely disturbed by propagating through artificial plasma regions. The scintillation levels for UHF waves passing through artificial ionization clouds from HAARP are typically 16 dB. This is much larger than previously reported scintillations at other HF facilities which have been limited to 3 dB or less. The goals of future HAARP experiments should be to build on these discoveries to sustain plasma densities larger than that of the background ionosphere for use as ionospheric reflectors of radio signals.

Artificial periodic irregularities in the high‐latitude ionosphere excited by the HAARP facility

AbstractWe present results of the new observations of artificial periodic irregularities (APIs) in the ionosphere using the High Frequency Active Auroral Research Program (HAARP) heating facility carried out in late May and early June 2014.The objective of this work is to detect API using high‐latitude facility and analyze possible differences of the temporal and spatial variations of the API echoes in the high (HAARP) and middle (Sura) latitudes. Irregularities were created by the powerful wave of X mode and were sounded using the short probing pulses signals of X mode. API echoes were observed in the D, E, and F regions of the ionosphere. Amplitudes and characteristic times of the API echoes were measured. The API growth and decay times at HAARP (high latitudes) observed were similar to those at the Sura heating facility (midlatitudes).