Excitation of an Additional Region of Short-Wavelength Plasma Oscillations in Ionospheric Heating Experiments

We discuss transfer of plasma waves, excited by a powerful radio wave due to its scattering on artificial ionospheric irregularities, into an additional region of very short plasma oscillations polarized almost perpendicular to the magnetic field. Such a region can exist in the magnetized ionospheric plasma due to the strong spatial dispersion. We take into account the plasma-wave diffusion over the spectrum caused by multiple scattering on irregularities, as well as the nonlinear process of plasma-wave interaction due to induced scattering by ions. The latter process leads to the transfer of primary plasma waves into the additional region. The induced scattering is considered in the differential approximation valid for sufficiently smooth plasma-wave spectra. The numerical calculations are performed for a Maxwellian plasma in which suprathermal electrons are absent. It is shown that in this case, the additional region of plasma waves is excited if the pump frequency is close to but slightly less than the fourth electron gyroharmonic, so that the absorption of primarily excited plasma waves becomes sufficiently strong. Application of our calculations to the results of ionospheric experiments is discussed.     

Background fluctuations in the GPS-microlab-1 ionospheric radio sounding experiment

We analyze the spectra of the phase and amplitude fluctuations of radio signals recorded in the course of four ionospheric radio-sounding sessions at altitudes from 70 to 120 km. Our study is aimed at determining the sources of these fluctuations. Comparing the statistical properties of fluctuations measured at two wavelengths with theoretical calculations, we conclude that only the low-frequency part of background fluctuations is of ionospheric origin, while the high-frequency fluctuations are caused by noise of the measuring system. The amplitude fluctuations are more informative in the high-frequency region, since they are mainly due to ionospheric irregularities. We discuss the possibility of separation of the components of amplitude fluctuations caused by ionospheric irregularities and the irregularities of the neutral atmosphere in the case of sounding at the altitudes at which those components have comparable values. It is shown that this problem cannot be solved by dispersion and extrapolation methods, which are used for separation of the regular ionospheric and atmospheric components of the amplitude and phase variations of radio signals. A. N. Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences, Moscow, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 42, No. 6, pp. 511–523, June 1999.     

Magnetogravity waves in the ionosphere under conditions of finite conductivity

We obtain dispersion relations for magnetogravity waves in the ionosphere with allowance for the combined influence of magnetic field, gravity, and finite conductivity within the framework of the hydrodynamic approximation. The required conditions are fulfilled in the ionosphere at altitudes over or about 250 km. The auroral electrojet is considered as a source of magnetogravity waves which are frequently observed as traveling ionospheric disturbances. The contribution of magnetogravity waves to the ionospheric disturbances is determined on the basis of analyzing the data from the vertical sounding of the ionospheric F₂ layer and the geomagnetic disturbances along the chosen magnetic meridian and on its sides. The features of the obtained dynamic spectra of magnetogravity waves agree with the characteristic frequencies and velocities determined by the calculated dispersion curves. As a result, we confirm the fact that magnetogravity waves stipulate some traveling ionospheric disturbances and can be used for diagnostics of the ionospheric parameters.     

A comparative study of the full dispersion relation, Compton dispersion relation, and Raman dispersion relation of a free-electron laser in helical wiggler and guiding magnetic fields

The full dispersion relation obtained for a free-electron laser in the presence of circularly polarized, periodic, static wiggler and guiding magnetic fields by the kinetic approach incorporating the particle trajectories is reduced to Compton and Raman regime approximations in the case of a tenuous electron beam. The temporal growth rate has been compared between the full dispersion relation and the Compton dispersion relation, as well as between the full dispersion relation and the Raman dispersion relation in the microwave region. The results show the maxima of growths in the full dispersion relation and the Compton dispersion relation, as well as the full dispersion relation and the Raman dispersion relation, are at the same locations, but the growth rates in both regimes are enhanced with respect to the full dispersion relation for the same plasma frequency and cavity parameters.     

Nonlinear instability of the ioncyclotron whistlers in presence of negative ions

This paper provides a theoretical investigation of the nonlinear propagation of ion cyclotron whistlers in presence of negative ions. First, it derives the dispersion relations from which group travel time of the ioncyclotron whistlers has been calculated. The ioncyclotron damping of the whistler due to the presence of negative ions and nonlinearity in the ionospheric plasma has also been studied here. The threshold power of the unstable proton whistler, the total attenuation and the generated magnetic field have been calculated. Finally possible applications of this study have been pointed out and the variation of different ionospheric parameters in different situations have been shown both numerically and graphically.The author is grateful to Prof. B. Chakraborty, Dept. of Mathematics, Jadavpur University; to Dr. K. P. Das, Dept. of Mathematics, Calcutta University; to Dr. S. N. Paul, Serampore Girls' College, Hooghly, West Bengal and to Dr. G. C. Das, Dept. of Mathematics, Manipur University for their helpful suggestions in the preparation of the article. The author is also grateful to the referee for his useful comments and suggestions which helped in bringing the paper in its present version.     

中低纬电离层加热大尺度场向不均匀体的二维数值模拟

大功率高频泵波加热电离层中,泵波反射高度区域是除了D,E层外的另一个主加热区.文中将在磁子午面内建立中低纬度地区泵波加热电离层中泵波反射高度处的二维模型,分别给出早晚两个时间模拟加热结果.根据模拟结果可知,整个泵波反射高度区域电子温度强烈上升,而泵波反射点周围电子浓度反而下降,该电子浓度空洞沿磁力线上下区域内电子浓度小幅上升,呈现出明显的场向特征.夜间模拟加热效应比早上更加明显,夜间、早上模拟平面内最大电子浓度变化率分别为-13%和-36%,电子温度变化率分别为88%和22%.另外在早晚的模拟加热中,电 关键词： 中低纬度 高频加热 数值模拟     

Transcontinental radio tomographic chain: First results of ionospheric imaging

The results of studying the structure of the ionospheric plasma distribution from data obtained at the transcontinental Russian radio tomographic chain, which is the world’s longest, are presented. The 4000 km long tomographic chain extends from the Svalbard Archipelago to Sochi. The unique feature of this upgraded radio tomographic system is that for the first time observations cover a wide sector of the ionosphere from high latitudes (polar cap and auroral region) to low latitudes. This allows us to study the transfer of perturbations in the system auroral-subauroral-midlatitude-low latitude ionosphere, and to analyze ionospheric electron density distributions in different latitudinal regions as a function of different external factors and solar-geophysical conditions. The first recent results speak for a complex structure of the ionospheric plasma, even in quiet geophysical conditions (K _p < 2.)     

Restoration of spectral characteristics of ionospheric wave disturbances

The problem of short-wave radio-signal reflection from a parabolic ionospheric layer with traveling ionospheric disturbances (TID) in the form of density waves is solved in an approximation of geometrical optics. Formulas that relate the arrival angle and Doppler shift of a radio signal to the TID parameters are derived by the small-perturbation method for the characteristic function. The inverse problem of determination of the TID spectral characteristics is solved. The amplitude, dispersion law, and propagation direction of ionospheric irregularitiesare restored.     

基于化学物质释放的电离层闪烁抑制方法研究

中低纬地区经常发生的电离层闪烁,严重影响卫星链路的无线电信号传播过程,导致卫星通信导航信号质量下降,甚至中断.在电离层闪烁发生前的酝酿生成期,通过向电离层闪烁"种子因素"的等离子体泡内释放电子密度增强类化学物质,填充等离子体泡,改变等离子体环境特性,调控电离层动力学过程,能够降低电离层等离子体不稳定性增长率,进而抑制闪烁的发生.本文开展了基于化学物质释放的电离层闪烁抑制理论及方法研究,根据化学物质释放对电离层等离子体环境的影响,定量计算控制因素改变对不稳定性增长率的贡献,建立了基于电子密度增强类化学物质释放的电离层闪烁抑制物理模型,仿真了等离子体泡的填充过程及等离子体不稳定性增长率的演化过程.仿真结果表明该方法具有较好的闪烁抑制效果,为我国中低纬地区卫星信号电离层闪烁抑制研究奠定了理论基础.     

Laboratory study of nonlinear trapping of magnetized Langmuir waves inside a density depletion

The formation of a small-scale plasma density depletion region extended along the ambient magnetic field and caused by the nonlinear interaction of the upper-hybrid plasma waves with a magnetoplasma has been observed under laboratory conditions modeling the ionospheric heating experiments. Plasma waves are trapped inside the depletion due to their specific dispersion properties. The threshold of the nonlinear wave trapping significantly increases in the vicinity of the harmonics of the electron gyrofrequency.     

Hole-interface optical phonon relaxation rates with valence band-mixing effects

We theoretically investigate the hole-interface optical phonon scattering rates for a InGaAs-AlGaAs quantum well structure, taking into account the valence-band mixing. The dispersion relation and the electrostatic potentials for interface optical phonon modes are obtained based on the macroscopic dielectric continuum model. For the hole dispersion relation, the Luttinger-Kohn Hamiltonian is used. The hole-interface optical phonon interaction is evaluated by the Fermi's golden rule taking into account the Bloch overlap factor.Our results show that the hole-interface phonon scattering rates within the parabolic band approximation are different from those including valence band mixing effects. Especially, in the low energy region, the hole-interface phonon scattering rates within the parabolic band approximation are overestimated very significantly.     

Sounding of the ionosphere disturbed by the “Sura” heating facility radiation using signals of the GPS satellites

We present the results of experimental studies of the properties of the plasma-density disturbances created during heating of the ionospheric F₂ region by high-power HF radio waves radiated by the “Sura” heating facility (Radiophysical Research Institute, Nizhny Novgorod). These experiments are specific in that they were performed in a sunlit (daytime) ionosphere when the generation of ionospheric turbulence has specific features and the turbulence intensity level is low enough. The plasma-density disturbances induced by high-power HF radio emission were sounded by signals of the GPS satellites, the line of sight to which crossed different parts of the disturbed ionosphere region. Threshold powers of the excitation of artificial plasma-density variations as well as spatial, temporal, spectral, and energy characteristics of the generated disturbances are determined.     

Spatial Autocorrelation of the Level of Radio Signal Amplitude at Oblique Propagation in the Ionosphere

Fluctuations of the amplitude level of a wave that propagates through a randomly inhomogeneous medium with regular reflection are considered. Analytical expressions for dispersion and amplitude correlation functions are derived in the parabolic model of a regular ionospheric layer inside the layer and at the exit from it. Special attention is paid to the study of the reflection area, where the conditions for the applicability of the geometric-optics method are violated. The results are analyzed numerically for ionospheric sounding under different conditions.     

Kelvin Helmholtz Instability in a Magnetoplasma

Two dimensional transverse Kelvin-Helmholtz (K-H) instability has been studied at the interface between the two fluids (plasma medium) of finite thickness in relative motion to each other. The perturbations on the interface are assumed to be electromagnetic and a dispersion relation is obtained. The interface (boundary) has been found to be unstable for a wide range of perturbation wavelengths (wave numbers kx, ky). It is shown that the modification introduced by electromagnetic (quasi-electrostatic) perturbations in comparison to electrostatic one is to reduce the growth rate of perturbations. The growth rate maximizes when kx = ky. The applications of this study have been discussed to explain some of the observed ionospheric (auroral arc formation) and magnetospheric (unstable magnetopause boundary, hydromagnetic pulsations) phenomena.     

Excitation of kinetic Alfvén waves by streaming ions in a dusty magnetoplasma with generalized (r,q) distribution function

We investigate the parallel streaming effects on the dispersion characteristics of a kinetic Alfvén wave (KAW) in a low β dusty magnetoplasma. To analyse the influence of streaming ions obeying generalized (r, q) distribution function, hot and magnetized electrons, and mobile charged dust, a theoretical approach has been used for the instability analysis by employing two potential theories. A linear kinetic dispersion relation of Alfvén waves is derived, whose solutions are used to interpret the numerical and analytical results. The solutions of dispersion relation indicate that the characteristics of KAWs are transformed when generalized (r, q) distribution function is employed instead of its Maxwellian counterpart. We also found that the unstable modes have a strong dependence on spectral indices r and q , dust parameters, and plasma β . For the excitation of KAWs, the streaming velocity has been observed to be within the sub-Alfvén range, whereas when it extends to the super-Alfvén range, the growth rates are significantly suppressed. The observations further show that an ambient magnetic field and superthermal particles inhibit the growth of an electromagnetic wave to a significant degree and have a stabilizing effect on the wave mode, whereas an increasing concentration of low-energy particles contributes to enhancing growth rates.     

The effect of spatial dispersion on the interaction of short-wavelength oscillations with small-scale plasma irregularities

Using the statistical random-phase approximation, we derive the equations describing the interaction of short-wavelength oscillations with irregularities of a magnetized plasma taking into account thermal effects of the spatial dispersion. It is shown that an additional energy exchange between the wave and the plasma electrons, which is not related to resonance particles or collisions, occurs in a medium with random irregularities due to the effect of spatial dispersion. This energy exchange can be significant if the scales of the irregularities along the magnetic field are not very large, so that the dispersion effects in the interaction of a wave with irregularities are greater than the dissipative ones. We consider in detail the case, typical for the ionosphere, where the irregularities are field-aligned and the plasma oscillations are polarized almost perpendicular to the magnetic field. An equation describing the differential redistribution of plasma-oscillation energy in the wavenumber space due to multiple scattering by the irregularities was obtained taking into account the influence of spatial dispersion on the scattering process. We discuss application of the results obtained to the interpretation of some ionospheric experiments. Institute for Solar-Terrestrial Magnetism, lonosphere, and Radio Wave Propagation of the Russain Academy of Sciences, Troitsk, Moscow region, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 43, No. 4, pp. 310–324, April, 2000.     

Focusing-defocusing phenomena of radio echo signal after passage of the morning solar terminator

Summary Campaign results of high-repetition ionospheric soundings, performed at the ionospheric station of Rome using a Digisonde 128P, are presented. We introduce an index derived from run rapid ionograms that can be used to detect oscillations of isodensity surfaces ofF ionospheric region started by morning solar terminator.     

Zur Ausbreitung von Ionenschall-Instabilitäten in schwach ionisierten Plasmen unter Berücksichtigung eines Potentialgradienten

A dispersion relation for the ion-acoustic instability in a dc-discharge is derived. The dc electric field term in the linearized Vlasov-equation is not neglected, and the ion drift velocity is taken into account. Collisions of the electrons and ions with the neutrals are considered on the basis of a Davy-dov-collision term. The influence of the dc field and the ion drift leads to higher values of the spatial growth rates in the low frequency range and a shift of the maximum of the growth rates and the high frequency boundary of the unstable waves toward lower frequencies. The phase velocity diminishes, what is, above all, a result of the consideration of the ion drift velocity.