An ionospheric modification experiment using very high power, high frequency transmission
TL;DR: In this paper, an experiment resulting in ionospheric modification of the F region through heating by an HF transmitting facility located near Boulder, Colorado, has begun, where a transmitter capable of producing nearly 2 Mw of average power, which, when used in conjunction with a 10-element ring array antenna, results in a power-aperture product of the order of 104 Mw m².
Abstract: An experiment resulting in ionospheric modification of the F region through heating by an HF transmitting facility located near Boulder, Colorado, has begun. This facility has a transmitter capable of producing nearly 2 Mw of average power, which, when used in conjunction with a 10-element ring array antenna, results in a power-aperture product of the order of 104 Mw m². Salient effects observed with radio-wave measurements after the heating transmitter had been turned on are: a prompt ionospheric response appearing within 30 sec as a deformation in the traces on ionosonde records; a development and growth of spread F starting within tens of seconds, frequently followed by multiple splitting of the O and X traces; appearance of a new time-varying broad-band echo which, at times, occurs after 10 min or more of heating and which changes in range with time; and a decrease, within 10 sec, of about 10 db in the amplitude of the O component alone, measured on an oblique path when heating with the O wave. Photometric measurements of 6300-A airglow from the heated region indicate about a 30% rise in electron temperature. Infrared radiation at 1.27 µ is enhanced in a region located down the magnetic field lines traversing the higher region initially heated by the radio wave.
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TL;DR: In this article, the authors present a review of the structure of the ionosphere and its properties, including the effect of nonlinearity on the Amplitude and Phase of the Wave.
Abstract: 1. Introduction.- 1.1 Data on the Structure of the Ionosphere.- 1.2 Features of Nonlinear Phenomena in the Ionosphere.- 1.2.1. Nonlinearity Mechanisms.- 1.2.2. Qualitative Character of Nonlinear Phenomena.- 1.2.3. Brief Historical Review.- 2. Plasma Kinetics in an Alternating Electric Field.- 2.1. Homogeneous Alternating Field in a Plasma (Elementary Theory).- 2.1.1.Electron Current-Electronic Conductivity and Dielectric Constant.- 2.1.2.Electron Temperature.- 2.1.3.Ion Current-Heating of Electrons and Ions.- 2.2. The Kinetic Equation.- 2.2.1. Simplification of the Kinetic Equation for Electrons.- 2.2.2. Transformation of the Electron Collision Integral.- 2.2.3. Inelastic Collisions.- 2.3. Electron Distribution Function.- 2.3.1. Strongly Ionized Plasma.- 2.3.2. Weakly Ionized Plasma.- 2.3.3. Arbitrary Degree of lonization-Concerning the Elementary Theory.- 2.4. Ion Distribution Function.- 2.4.1. Simplification of the Kinetic Equation.- 2.4.2. Distribution Function.- 2.4.3. Ion Temperature, Ion Current.- 2.5. Action of Radio Waves on the Ionosphere.- 2.5.1. lonization Balance in the Ionosphere.- 2.5.2. Effective Frequency of Electron and Ion Collisions-Fraction of Lost Energy.- 2.5.3. Electron and Ion Temperatures in the Ionosphere.- 2.5.4. Heating of the Ionosphere in an Alternating Electric Field.- 2.5.5.Perturbations of the Electron and Ion Concentrations.- 2.5.6. Artificial lonization of the Ionosphere-Heating of Neutral Gas.- 3. Self-Action of Plane Radio Waves.- 3.1. Simplification of Initial Equations.- 3.1.1. Nonlinear Wave Equation.- 3.1.2. Nonlinear Geometrical Optics of a Plane Wave.- 3.2. Effect of Nonlinearity on the Amplitude and Phase of the Wave.- 3.2.1. Self-Action of a Weak Wave.- 3.2.2. Self-Action of a Strong Wave.- 3.2.3. Self-Action of Waves in the Case of Artificial lionization.- 3.3. Change of Wave Modulation.- 3.3.1. Weak Wave.- 3.3.2. Change of Amplitude Modulation of Strong Wave.- 3.3.3. Phase Modulation.- 3.3.4. Nonlinear Distortion of Pulse Waveform.- 3.4. Generation of Harmonic Waves and Nonlinear Detection.- 3.4.1. Frequency Tripling.- 3.4.2. Nonlinear Detection.- 3.5. Self-Action of Radio Waves in the Lower Ionosphere.- 4. Interaction of Plane Radio Waves.- 4.1. Cross Modulation.- 4.1.1. Weak Waves.- 4.1.2. Strong Perturbing Wave.- 4.1.3. Resonance Effects near the Electron Gyrofrequency.- 4.2. Interaction of Unmodulated Waves.- 4.2.1. Interaction of Short Pulses.- 4.2.2. Change in the Absorption of a Wave Propagating in a Perturbed Plasma Region.- 4.2.3. Generation of Waves with Combination Frequencies.- 4.3. Radio Wave Interaction in the Lower Ionosphere.- 4.3.1. Cross Modulation.- 4.3.2. Fejer's Method.- 4.3.3. Nonstationary Processes in the Interaction of Strong Radio Waves.- 5. Self-Action and Interaction of Radio Waves in an Inhomogeneous Plasma.- 5.1. Inhomogeneous Electric Field in a Plasma.- 5.1.1. Fundamental Equations.- 5.1.2. Distribution of Density and Temperatures in Plasma.- 5.2. Kinetics of Inhomogeneous Plasma.- 5.2.1. Kinetic Coefficients. Elementary Theory.- 5.2.2. Kinetic Theory.- 5.2.3. Fully Ionized Plasma.- 5.3. Modification of the F Region of the Ionosphere by Radio Waves.- 5.3.1. Modification of the Electron Temperature and of the Plasma Concentration.- 5.3.2. Radio Wave Reflection Region.- 5.3.3. Growth and Relaxation of the Perturbations.- 5.4. Focusing and Defocusing of Radio Wave Beams.- 5.4.1. Nonlinear Geometrical Optics.- 5.4.2. Defocusing of Narrow Beams.- 5.4.3. Mutual Defocusing.- 5.4.4. Thermal Focusing in the Lower Ionosphere.- 6. Excitation of Ionosphere Instability.- 6.1. Self-Focusing Instability.- 6.1.1. Spatial Instability of a Homogeneous Plasma.- 6.1.2. Instability in the Wave-Reflection Region.- 6.2. Resonant Absorption and Resonance Instability.- 6.2.1. Langmuir Oscillations in an Inhomogeneous Plasma.- 6.2.2. Excitation of Plasma Waves.- 6.2.3. Resonance Instability.- 6.2.4. Absorption of Ordinary Radio Waves.- 6.3. Parametric Instability.- 6.3.1. Langmuir Oscillations of a Plasma in an Alternating Field.- 6.3.2. Parametric Excitation of Langmuir Oscillations.- 6.3.3. Parametric Instability in the Ionosphere.- 6.3.4. Dissipative Parametric Instability.
481 citations
TL;DR: In this paper, the authors derived thresholds and linear growth rates for stimulated Brillouin and Raman scattering and for the parametric decay instability by using arguments of energy transfer.
Abstract: Thresholds and linear growth rates for stimulated Brillouin and Raman scattering and for the parametric decay instability are derived by using arguments of energy transfer. For this purpose an expression for the ponderomotive force is derived. Conditions under which the partial pressure force due to differential dissipation exceeds the ponderomotive force are also discussed. Stimulated Brillouin and Raman scattering are weakly excited by existing incoherent backscatter radars. The parametric decay instability is strongly excited in ionospheric heating experiments. Saturation theories of the parametric decay instability are therefore described. After a brief discussion of the purely growing instability the effect of using several pumps is discussed as well as the effects of inhomogeneity. Turning to detailed theories of ionospheric heating, artificial spread F is discussed in terms of a purely growing instability where the nonlinearity is due to dissipation. Field-aligned short-scale striations are explained in terms of dissipation of the parametrically excited Langmuir waves (plasma oscillations); they might be further amplified by an explosive instability (except at the magnetic equator). Broadband absorption is probably due to scattering of the electromagnetic pump wave into Langmuir waves. This absorption is probably responsible for the ‘Overshoot’ effect: the initially observed level of parametrically excited Langmuir waves is much higher than the steady state level.
296 citations
TL;DR: In this paper, an extension of the emission term to include the effects of nonlinear plasma waves and a numerical integration of the wave kinetic equation was proposed to find the saturation state of parametric instabilities when the wave intensity has axial symmetry about the pump field in wave number space.
Abstract: Parametric instabilities, excited in the ionosphere by high-power HF transmitters with a frequency below the maximum ionospheric plasma frequency, produce nonlinear energy absorption and enhanced scattering of electromagnetic radiation, which has been detected by the Arecibo Thomson scatter radar. This paper reviews and extends both the linear and nonlinear saturation theory of parametric instabilities within the ionospheric context. The new elements are a modification of the emission term to include the effects of nonlinear plasma waves and a numerical integration of the wave kinetic equation to find the saturation state of parametric instabilities when it is assumed only that the wave intensity has axial symmetry about the pump field in wave number space. Calculations are presented of the magnitude of the nonlinear energy absorption and of the angular dependence, frequency spectrum, and intensity of scattering from instability-created density fluctuations. In the present experiments the nonlinear processes are predicted to absorb roughly 30% of the radio wave energy incident on the ionosphere. As a rule, this energy is deposited in the high-energy tail of the electron velocity distribution and causes enhanced airglow. The scattered radiation has a frequency shift almost equal to the modifier frequency, and its intensity depends strongly on the angle between k and E0, k being the wave vector of the plasma wave responsible for the scattering and E0 the pumping electric field produced by the modification transmitter. Because the instabilities occur only with O mode transmissions, the direction of E0 is close to the geomagnetic field. The angular dependence result rests on a combination of two-dimensional saturation calculations and plasma wave refraction due to propagation in the inhomogeneous magnetoactive ionospheric plasma. For example, the plasma waves responsible for the scattering observed at Arecibo are found to be nonlinearly stabilized and roughly 104 times less intense than plasma waves propagating within 20° of the geomagnetic field. Thus the scattering observed at Arecibo, although it is intense by Thomson scatter standards, is predicted to be ∼40 dB below the scattering observable in the most favorable geometry. Lastly, new aeronomy experiments made possible by parametric instabilities are discussed.
225 citations
01 Jul 1989
TL;DR: The role played by the anomalous absorption of the high power wave is discussed in this article, with the relative importance of collisional and anomalous heating at the high latitude site is examined.
Abstract: The high power radio facility, built jointly by the Max-Planck-Institut fur Aeronomie, Lindau and the University of Tromso, at Tromso in Northern Norway, has been operational since 1980. Since that time an extremely wide range of ionospheric modification phenomena, induced by the powerful radio beam or pump, has been studied by a multitude of diagnostic techniques. This review is concerned, in particular, with the role played by the anomalous absorption of the high power wave. Anomalous absorption arises when the high power electromagnetic waves excite thermal parametric plasma instabilities in the diffusion dominated ionospheric F-region. This leads to the growth of plasma density irregularities, which are highly elongated along the geomagnetic field and which very efficiently couple electromagnetic and electrostatic plasma waves. The conversion of the electromagnetic modifying wave to rapidly damped electrostatic waves constitutes the anomalous absorption process which gives rise to strong plasma heating and the self extinction of the pump. After briefly reviewing some relevant results from earlier experiments carried out in the USA, a number of modification experiments undertaken at Tromso, using both HF diagnostics and the European Incoherent Scatter radar (EISCAT), are described in detail. These experiments were designed to investigate anomalous absorption processes, large scale plasma heating, pump self action and cross-modulation effects. The relevant theories required to interpret these experimental results are also presented. In particular, the relative importance of collisional and anomalous heating at the high latitude site is examined. The importance of the Tromso high power facility to aeronomical studies is also briefly discussed.
200 citations
TL;DR: In this paper, a number of enhancements of the incoherent scatter spectrum excited by strong high frequency (HF) radio waves were observed during an ionospheric heating experiment in January at Arecibo, where significant time variations over scales of tens of µsec through hours were seen.
Abstract: Observations are reported of enhancements of the incoherent scatter spectrum excited by strong high frequency (HF) radio waves. A number of enhancement characteristics, observed during an ionospheric heating experiment in January at Arecibo, are described. The enhancement spectrum includes: a strong narrow line displaced below the HF (5.62 MHz) by the frequency of the ion acoustic waves fi in the plasma (about 4 kHz); a broader line (about 30-kc width) and other weak lines near the HF; and a line near fi. Enhancements above thermal levels range above a factor of 104 and may be taken as verification of the HF excitation of parametric instabilities in the ionosphere. Significant time variations over scales of tens of µsec through hours were seen. Upshifted and downshifted enhanced plasma lines display asymmetries in intensity, width, power dependence, and decay rates (of the order of msec). The O-mode (but not the X-mode) excitation of these enhancements is of significance to heating experiments.
137 citations
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TL;DR: In this paper, the authors investigated the role of self-action in the propagation of a radio wave in the ionosphere of a homogeneous electric field and showed that the effect of cross-modulation in Isotropic Plasmas can be seen as a function of the number of collisions with neutral particles.
Abstract: Introduction 139 1. Plasma in a Homogeneous Electric Field (Elementary Theory) 141 1.1. Electron Current. Dielectric Permittivity and Conductance of Plasma 141 1.2. Electron Temperature 143 2. Plasma in Homogeneous Electric Fields (Kinetic Theory) 147 2.1. Kinetic Equation 147 2.2. Transformation of the Collision Integral 150 a) Elastic Collisions with Neutral Particles (Molecules) 150 b) Inelastic Collisions with Neutral Particles 152 c) Collisions with Ions 153 d) Collisions between Electrons 154 2.3. Solution of Kinetic Equation. Stronglyionized Plasma 155 a) Distribution Function (Maxwellian Distribution) 156 b) Effective Number of Collisions 158 c) Relative Fraction of Energy Transfer 158 d) Electron Current. Dielectric Permittivity and Conductance of Plasma 159 e) Electron Temperature 162 2.4. Weakly-ionized Plasma 163 a) Case of Elastic Collisions 163 b) Molecular Plasma 164 c) Inert Gases 165 d) Electron Current and Average Electron Energy 166 2.5. Arbitrary Degree of Ionization. Elementary Theory 166 a) Transition for Strongly-ionized to Weakly-ionized Plasma 166 b) Conditions of Validity of Elementary Theory 168 3. Nonlinear Effect in the Propagation of Radio Waves in a Plasma (Ionosphere) 3.1. Propagation of a Radio Wave in a Plasma with Allowance for Nonlinearity (Self Action of the Plasma) 3.2. Role of Self Action of a Plasma in the Propagation of Waves in the Ionosphere a) Short Waves (λ≤ 200 m; ω ≥ 107). b) Average Waves (200 2000 m; ω < 106). d) Resonant Self-remodulation near the Gyro Frequency 3.3. Nonlinear Interaction of Modulated Radio Waves (Cross Modulation), a) Cross Modulation in Isotropic Plasma, b) Calculation of the Effect of a Permanent Magnetic Field. Resonant Effects near the Gyro Frequency 3.4. Results of Experimental Investigations of Cross Modulation in the Ionosphere. a) Absolute Value of Depth of Cross Modulation, b) Dependence of μΩ and ΦΩ on μ0 and Ω, n) Dependence of μΩ on the Power of the Interfering Station, d) Dependence of μΩ on the Frequencies ω1 and ω2. e) Resonance of Cross Modulation at ω1 ~ ωH. 3.5. Nonlinear Interaction of Unmodulated Radio Waves, a) Variation of Conditions of Wave Propagation, b) Sideband Waves (Waves with Combination Frequencies). c) Nonlinear Effects Connected with Variation of the Electron Concentration Concluding Remarks Literature Cited
204 citations
TL;DR: In this paper, the authors investigated the possibility of artificially heating the electrons in the F region by means of a radio wave and derived equations for the steady-state values of the electron density and electron temperature profiles as a function of the transmitter parameters and the initial state of the ionosphere.
Abstract: The possibility of artificially heating the electrons in the F region by means of a radio wave is investigated. On the basis of a somewhat oversimplified model of the actual problem, equations are derived for the steady-state values of the electron density and electron temperature profiles as a function of the transmitter parameters and the initial state of the ionosphere. These equations are then solved numerically for several cases of interest. At a frequency of 50 Mc/s, slight but probably detectable changes in the ionosphere could be produced by means of a large antenna and an average transmitter power of the order of 500 kw or more. At higher frequencies, or for smaller average powers, the effects are negligible. Thus heating is unlikely to complicate incoherent scattering measurements in the F region. By using frequencies very near the F-region penetration frequency, however, it is possible to achieve much larger effects because of the resonant absorption. Using only 50–100 kw and a sufficiently large antenna we could change the electron temperature by a few hundred degrees. Using higher powers, much larger changes are possible. Detailed measurements of the heating effects could provide considerable data on transport phenomena in the ionospheric plasma. The experiment would also provide a convenient way of studying a nonequilibrium plasma under fairly controlled conditions.
174 citations
TL;DR: In this article, radio reflectivity was used to study the F-region ionospheric modifications produced by the installation described by Utlaut [1970] in a companion paper.
Abstract: Several radio techniques are being employed to study the F-region ionospheric modifications produced by the installation described by Utlaut [1970] in a companion paper. One such technique, discussed here, is the measurement of ‘radio reflectivity,’ the relative power of radio echoes obtained from the perturbed ionosphere. Some theoretical aspects of this technique and its potential for measuring ionospheric parameters are treated in a companion paper by Whitehead [1970]. Preliminary measurements using the technique are reported here. These measurements yielded unexpected results whose possible interpretation is tentatively presented.
61 citations
TL;DR: In this article, the authors describe detection of significant changes in the electron temperature in the F2 region produced by absorption of radio-frequency energy propagated at or near the local ionospheric plasma frequency.
Abstract: In recent years methods of producing controlled modifications of the ionosphere by use of high-intensity radio-frequency waves have been proposed; some have been tried with inconclusive results. The present paper describes detection of significant (∼30%) changes in the electron temperature in the F2 region produced by absorption of radio-frequency energy propagated at or near the local ionospheric plasma frequency. The radio-frequency source is the 1-Mw cw transmitter and ∼16° beamwidth antenna array described in the accompanying paper by Utlaut [1970]. As shown by the calculations of Meltz and LeLevier [1970], electron temperature increases of ∼35% can be expected within a few tens of seconds after the transmitter, tuned to within 1% of f0F2, is turned on.
58 citations
TL;DR: The heating and hydrodynamic expansion of the F layer caused by absorption of an incident radio wave occurs in several phases as discussed by the authors, and the incident wave field is almost unperturbed.
Abstract: The heating and hydrodynamic expansion of the F layer caused by absorption of an incident radio wave occurs in several phases. During the first minute, energy is imparted to the electron gas through ohmic dissipation, the electron temperature is raised, field-aligned pressure gradients are established, and the plasma begins to expand along the magnetic field. Plasma density changes are small, less than 1%, during this initial phase and the incident wave field is almost unperturbed. During the next several minutes, the plasma accelerates and the F-region density is reduced, albeit slowly, while the electron and ion temperatures approach steady state.
55 citations