Electromagnetic inertio-gravity waves in the Earth's ionosphere

Propagation of electromagnetic inertio-gravity (IG) waves in the partially ionized ionospheric E- and F-layers is considered in the shallow water approximation. Accounting of the field-aligned current is the main novelty of the investigation. Existence of two new eigen-frequencies for fast and slow electromagnetic waves is revealed in the ionospheric E-layer. It is shown that in F-layer slowly damping new type of inertial-fast magnetosonic waves can propagate. Slowly damping low-frequency oscillations connected with the field-aligned conductivity are found. Broad spectrum of oscillations is investigated.     

Dynamics of the large-scale ULF electromagnetic wave structures in the ionosphere

The present article displays the results of theoretical investigation of the planetary ultra-low-frequency (ULF) electromagnetic wave structure, generation and propagation dynamics in the dissipative ionosphere. These waves are stipulated by a spatial inhomogeneous geomagnetic field. The waves propagate in different ionospheric layers along the parallels to the east as well as to the west and their frequencies vary in the range of (10–10⁻⁶) s⁻¹ with a wavelength of order 10³ km. The fast disturbances are associated with oscillations of the ionospheric electrons frozen in the geomagnetic field. The large-scale waves are weakly damped. They generate the geomagnetic field adding up to several tens of nanotesla (nT) near the Earth's surface. It is prescribed that the planetary ULF electromagnetic waves preceding their nonlinear interaction with the local shear winds can self-localize in the form of nonlinear long-living solitary vortices, moving along the latitude circles westward as well as eastward with a velocity different from the phase velocity of the corresponding linear waves. The vortex structures transfer the trapped particles of medium, as well as energy and heat. That is why such nonlinear vortex structures can be the structural elements of the ionospheric strong macro-turbulences.     

Amplification and energy transformation of the magnetized Rossby waves in the ionosphere with an inhomogeneous zonal wind. I. A theory

The generation and further dynamics of the planetary magnetized Rossby waves and inertial waves in a dissipative ionosphere in the presence of a smooth inhomogeneous zonal wind (shear flow) have been studied. The magnetized Rossby waves are caused by the interaction with the spatially inhomogeneous geomagnetic field and represent the ionospheric manifestations of usual tropospheric Rossby waves. The effective linear mechanism of amplification and mutual transformation of the Rossby and inertial waves has been revealed. For shear flows, the operators of linear problems are not self-adjoint, and the corresponding eigenfunctions are non-orthogonal; therefore, a canonical modal approach is of little use in studying such motions. It becomes necessary to apply the so-called nonmodal mathematical analysis, which has actively been developed for the last years. The nonmodal approach makes it possible to reveal that the transformation of wave-like disturbances in shear flows is caused by the nonorthogonality of eigenfunctions in the problem of linear dynamics. Thus, there appear a new degree of the system freedom and a new way of disturbance evolution in the medium.     

Features of resonance structures in natural electromagnetic noise spectra in the region of the main ionospheric trough

The paper presents the results of studies of the resonance structures of the background electromagnetic noise spectrum obtained in a series of experiments in the autumn of 2012 in Karelia. The experiments are unique because the background noise was detected at stations spaced by a distance much less than the doubled effective waveguide height (about 50 km) in a region close to the main ionospheric trough, the structure and position of which were determined based on radiotomographic data. It is shown that the dimensions of the ionospheric local region, which affects both the generation of spectral resonance structures in particular and the propagation of electromagnetic waves in the considered range in general, depend significantly on the variation of ionospheric parameters in regions with strong horizontal inhomogeneity.     

THE EARTH'S IONOSPHERE: A WALL-LESS PLASMA LABORATORY

The earth's ionosphere possesses plasma properties at altitudes above 80 km where the collisions of charged particles with the neutral gas gradually lose their dominating influence. The ionosphere can be characterized as a weakly ionized low- and low-temperature plasma of great homogeneity with respect to the spatial scales of most of the processes of interest. The basic properties of the ionospheric plasma are presented in Section 2.1. The role of thermal fluctuations and their use in a powerful diagnostic technique -- the incoherent scatter technique -- are reviewed in Section 2.2. Plasma instabilities of natural cause, occurring in different altitude regions, are briefly discussed in Sections 2.3 and 2.4. The major part of this article is devoted to active experiments in the ionospheric plasma, as initiated by powerful electromagnetic waves transmitted from the ground, and their theoretical understanding (Section 3). Nonlinear effects caused by strong electromagnetic waves are numerous, but they can be traced to either of two nonlinearity mechanisms, thermal or ponderomotive. Thermal nonlinearities in a homogeneous wave field are briefly sketched in Section 3.1. Thermal nonlinearities in an inhomogeneous wave field, having their origin in pressure gradient forces and resulting in two different types of density irregularities, both aligned with the magnetic field, are treated in Section 3.2. Ponderomotive nonlinearities have their source in the convective derivative in the electron momentum equation which gives rise to a force that pushes plasma from high to low wave intensity. Specific phenomena caused by ponderomotive action are Langmuir turbulence and stimulated electromagnetic emissions (SEE). Both these phenomena are presently the subjects of intensive experimental and theoretical investigations, and they are described at some length in Section 3.3.     

Mechanism by which frontal structures in the ionospheric sporadic E layers are formed

A mechanism by which frontal structures in the ionospheric E region are formed, based on the Ekman-type instability in the neutral component of a weakly ionized ionospheric plasma, when it is important to take into account large-scale wind helicity and neutral component turbulence, is proposed.     

Usage of regularization techniques for effective electron collision frequency determination from oblique ionospheric sounding

Computer modelling is used to investigate the possibility of determining ionospheric parameters from slightly oblique ionospheric soundings, using absorption data for decametric radio waves of different polarization. It is shown that with mean square measurement errors of 0.5 dB, and using regularization algorithms to solve the inverse problems, electron collision frequency profiles can be obtained for the night F-region with errors of less than 30%. Both temperatures of electrons and neutrals are also determined to within 10%.     

温度各向异性电子束流和电子环束流引起的电磁辐射特征

利用一维三分量完全电磁粒子模拟方法研究了由温度各向异性电子束流和电于环束流引起电磁辐射特征,结果表明它们都能激发高频宽带电磁不稳定性,其中环束流不稳定性（RBI）的非线性饱和水平比温度各向异性束流不稳定性（TABI）强,对RBI波在系统发展的线性增长阶段呈右旋极化,在非线性饱和阶段则主要呈左旋极化,而对TABI波在系统发展的整个阶段均享右旋极化．这些结果可应用于磁化星磁层射电暴的解释中．     

低纬地区电离层电流的人工调制数值模拟

利用高频泵波能对低电离层进行有效的人工扰动.采用ELF/VLF调幅高频电波对电离层进行加热,电子温度会随着调制频率振荡,并引起电导率周期性变化,从而使加热区内电离层电流周期性变化,形成等效的ELF/VLF电离层虚拟天线,辐射调制频率范围内的无线电波.早期的电离层人工调制研究主要集中在高纬和极区,本文讨论低纬地区电离层人工调制的可能性.本文的理论研究和数值模拟结果表明,低纬地区低电离层电导率在周期性加热的条件下能有效地被调制,使加热区域形成ELF/VLF波的电流辐射源,并分析了不同加热参数和入射条件对调制效果的影响.     

尘埃等离子体微波衰减常数的理论分析

将固体火箭喷焰看作弱电离尘埃等离子体，在统计理论框架下，通过求解含碰撞项的Blotzmann方程和Shukla方程，给出了弱电离尘埃等离子体复电导率和衰减常数计算公式，提出了充电响应因子的概念.将固体火箭喷焰的有关参数代入计算表明，衰减常数同时受电子和尘埃粒子浓度以及尘埃粒子半径的影响.理论的分析与实验所观测到的现象一致.     

Excitation of VLF quasi-electrostatic oscillations in the ionospheric plasma

A numerical solution of the dispersion equation for electromagnetic waves in a hot magnetized collisionless plasma has shown that, in a current-free ionospheric plasma, the distortion of the electron distribution function reproducing the downward flow of a thermal electron component and the compensating upward flow of the suprathermal electrons, which are responsible for the resulting heat flux, can destabilize quasi-electrostatic ion sound waves. The numerical analysis, performed with ion densities and electron temperature taken from the data recorded by the Interkosmos-24 (IK-24, Aktivny) satellite, is compared with a VLF spectrum registered at the same time on board. This spectrum shows a wide frequency band emission below the local ion plasma frequency. The direction of the electron heat flux inherent to the assumed model of VLF emission generation is discussed.     

The association of the residual error of dual-frequency Global Navigation Satellite Systems with ionospheric turbulence parameters

The effects of ionospheric scintillation on the residual error of the dual-frequency Global Navigation Satellite System are investigated. For the ordinary and extraordinary waves the scalar wave equations are obtained to a high-frequency approximation from the Maxwell equations. The solution for these scalar equations to the second-order Rytov approximation made it possible to determine the residual error up to the third order taking into account the ionospheric anisotropy and diffraction effects appearing when the signal is propagating through a turbulent ionospheric plasma. It is shown that the third-order effects, associated with scintillation, that is, with the propagation of the signal through a randomly inhomogeneous ionosphere, can be dominant and exceed second-order effects associated with the influence of the geomagnetic field. We investigate the association of the residual error with such parameters of ionospheric turbulence as the variance, and the inner and outer scales.     

Numerical simulation of the mutual conversion of ordinary and extraordinary waves in a magnetised plasma by artificial ionospheric turbulence

Some effects of normal mode coupling in weakly anisotropic inhomogeneous plasma are analysed on the basis of the numerical solution of transfer equations for the Stokes parameters. The numerical analysis of normal mode conversion on a set of isolated irregularities demonstrates the possibility of an effective polarisation transformation on such structures. It is shown that by the appropriate selection of discrete irregularities of the external magnetic field direction or plasma electron concentration resulting in radio-wave refraction, one can control electromagnetic radiation polarisation characteristics. Analytical expressions for mean Stokes parameters have been obtained for the rare isolated irregularities. The opportunity for the simulation of mutual wave conversion processes in the ionospheric heating experiments is discussed.     

具有非线性地形的正压流体中孤立Rossby波的mKdV方程

正压流体中,采用摄动方法将准地转位涡方程推导出地形效应的mKdV方程,得到Rossby波振幅的演变满足地形效应的mKdV方程的结论,说明地形效应是诱导Rossby孤立波的重要因素.     

Manifestation of gravitational tides and planetary waves in long-term variations in geophysical parameters

Long-term variations in the parameters of the Earth’s upper atmosphere and geophysical activity have been studied based on the current spectra. The main sources of quasiperiodic oscillations in the atmosphere (including variations in the solar radiation, geomagnetic activity, and gravity) have been considered. It was shown that the most stable quasiharmonic variations are related to tidal gravitational oscillations and Rossby planetary waves with stable spectra. These oscillatory processes substantially contribute to the dynamics of the middle and upper atmosphere and manifest themselves in ionospheric parameters.     

Rossby波的螺旋斑图

应用描写大气大尺度运动的准地转方程组，求得了大气Rossby波的三维定常流场以及相应的位温场、涡度场和散度场，其中的三维流场构成了物理空间的一个非线性自治动力系统. 研究表明，Rossby波具有     

Interaction of upper and lower hybrid waves and generation of the downshifted maximum feature of stimulated electromagnetic emissions

The decay of an upper hybrid (UH) wave to a lower hybrid (LH) wave and a daughter upper hybrid wave is considered. The linear stage of the process was analyzed for ionospheric conditions and compared with experimental data as well as with theoretical results of other authors. It was shown that the effective excitation of the prominent downshifted maximum feature of stimulated electromagnetic emissions in the ionospheric modification experiments could take place possibly due to interaction between two oblique UH waves and a heavily damped LH wave.     

Radio emission spectrum from an interplanetary shock front

The characteristics of low-damping high-frequency waves in hot magnetized solar and stellar coronal plasmas under the conditions when the electron gyrofrequency ω_He is equal to or higher than the electron plasma frequency ω_pe have been analyzed using the numerical solution of the dispersion equation. It is shown that the wave branches corresponding to the Z mode and ordinary waves approach each other when the magnetic field increases and become almost indistinguishable in a wide frequency range at all angles between the wave vector and magnetic field. A branch with anomalous dispersion appears at angles close to 90°. A new interpretation of broadband pulsations and spikes is suggested on the basis of the results.     

High-frequency waves in hot magnetized solar and stellar coronal plasmas

The characteristics of low-damping high-frequency waves in hot magnetized solar and stellar coronal plasmas under the conditions when the electron gyrofrequency ω_He is equal to or higher than the electron plasma frequency ω_pe have been analyzed using the numerical solution of the dispersion equation. It is shown that the wave branches corresponding to the Z mode and ordinary waves approach each other when the magnetic field increases and become almost indistinguishable in a wide frequency range at all angles between the wave vector and magnetic field. A branch with anomalous dispersion appears at angles close to 90°. A new interpretation of broadband pulsations and spikes is suggested on the basis of the results.