Influence of the Angular Distribution of Langmuir Waves on the Directivity of Radio Emission at Double Plasma Frequency

Geomagnetism and Aeronomy - The directivity of transverse electromagnetic waves generated in a plasma at a double plasma frequency during the coalescence of plasma waves is calculated for various...     

Simulation of Physical Phenomena in the Ionosphere and Magnetosphere of the Earth on Krot Plasma Device. Some Results and Prospects

Krot device is a unique installation of the scientific infrastructure of the Russian Federation. It is a source of highly uniform low-temperature plasma that takes up to several tens of cubic meters. The setup makes it possible to perform both scaling laboratory simulations of ionospheric and magnetospheric phenomena in the approximation of unbound plasma, as well as plasma tests of full-size samples of the onboard equipment of spacecraft (SC). The simulation results of the dynamics and interaction of small-scale thermal plasma irregularities occurring during ionospheric heating experiments are presented. The impedance of the small-size models of RESONANCE and STRANNIK SC electric antennas in plasma is measured. The possible use of free-space calibration of antennas in the magnetospheric portions of the orbit in the ELF and VLF ranges is confirmed. The efficiency of a new plasma parameters resonance sensor for the TRABANT SC in the ionospheric range of electron densities is shown.     

Transport of thermal plasma above the auroral ionosphere in the presence of electrostatic ion-cyclotron turbulence

The electron component of intensive electric currents flowing along the geomagnetic field lines excites turbulence in the thermal magnetospheric plasma. The protons are then scattered by the excited electromagnetic waves, and as a result the plasma is stable. As the electron and ion temperatures of the background plasma are approximately equal each other, here electrostatic ion-cyclotron (EIC) turbulence is considered. In the nonisothermal plasma the ion-acoustic turbulence may occur additionally. The anomalous resistivity of the plasma causes large-scale differences of the electrostatic potential along the magnetic field lines. The presence of these differences provides heating and acceleration of the thermal and energetic auroral plasma. The investigation of the energy and momentum balance of the plasma and waves in the turbulent region is performed numerically, taking the magnetospheric convection and thermal conductivity of the plasma into account. As shown for the quasi-steady state, EIC turbulence may provide differences of the electric potential of δ V ≈ 1–10 kV at altitudes of 500 < h < 10 000 km above the Earth’s surface. In the turbulent region, the temperatures of the electrons and protons increase only a few times in comparison with the background values.     

The Influence of the Hydrodynamic Response of the Flare Plasma on the Kinetics of an Accelerated Electron Beam and Hard X-rays

Geomagnetism and Aeronomy - The transfer of accelerated electrons in the plasma of flaring loops is accompanied by a hydrodynamic response of the heated plasma. The dynamics of the accelerated...     

Effectiveness of fast electron retention in the magnetic cavern during disturbance of the magnetic field azimuthal symmetry

The loss rate of fast electrons (with an energy much higher than the energy of the plasma electron thermal motion), when they leave a magnetic cavern during a disturbance of the magnetic field azimuthal symmetry, is studied. The cases of point and volume sources of fast particles have been considered. The plasma density in the cavern is supposed to be low, so that collisions of fast electrons with plasma particles can be neglected. The effect of the electric field on particle motion is neglected because it is assumed that the electric charge particles outgoing from the cavern is compensated by the counter current of plasma conductivity electrons. The dependence of the loss value on the harmonic number and the amplitude of the cavern boundary radius disturbance has been obtained.     

Turbulent transport of the Earth magnitisphere: Review of the results of observations and modeling

The results of observations of turbulent transport in the Earth’s magnetosphere tail are summarized. The results of recent works on the projection of the auroral oval onto the equatorial plane, according to which the main part of the oval is not projected onto the plasma sheet, are taken into account. Analysis of the eddy diffusion coefficient dependences on the geocentric distance and on the phase of a magnetosphere substorm, both across the sheet and in the azimuthal direction, is carried out. The role of eddy diffusion in the creation of quasi-equilibrium plasma structures and in the plasma transport from the magnetospheric flanks into the plasma sheet is considered. The transport along the sheet is discussed. The problems of turbulent transport that can be solved by analysis the data of multisatellite projects are indicated.     

Guided waves in the plasma sheet and triggering of a substorm

A guided propagation of magnetoacoustic wave in the plasma sheet located between two lobes of the magnetotail is investigated. The dispersion equation for the wave and equation connecting a disturbance of plasma pressure inside the plasma sheet and amplitude of the plasma sheet boundary oscillations are obtained. For some value of plasma pressure disturbance, the displacement of the plasma sheet boundaries becomes of order of the half-thickness of the plasma sheet. In the case of symmetrical oscillations of the boundaries (“sausage-like” mode), it creates the favorable conditions for reconnection of the magnetic field lines in the magnetotail and may lead to triggering of a substorm. The magnetoacoustic wave may be generated by sudden impulse of the solar wind plasma pressure.     

Electromagnetic waves in the auroral and subauroral regions of the topside ionosphere

The density and temperature of the plasma electron component and wave emission intensity in the topside ionosphere were measured by the INTERCOSMOS-19 satellite. In the subauroral ionosphere, a decrease in the plasma density correlates with an increase in the plasma electron component temperature. In this case, the additional increase in the electron component temperature was measured in regions with increased plasma density gradients during the substorm recovery phase. In a linear approximation, the electromagnetic wave growth increments are small on electron fluxes precipitating in the auroral zone. It has been indicated that Bernstein electromagnetic waves propagating in the subauroral topside ionosphere can intensify in regions with increased plasma density gradients on electron fluxes orthogonal to the geomagnetic field, which are formed when plasma is heated by decaying electrostatic oscillations of the plasma electron component. This can be one of the most important factors responsible for the intensification of auroral kilometric radiation.     

土星磁层等离子体径向输运的数值模拟

本文建立了一个包含离心力效应的自洽稳态土星磁层模型,并且用等离子体细丝模型对土星磁层等离子体径向输运进行了数值模拟.模拟结果表明,Dione（土卫四）附近的等离子体可能因为发生离心交换不稳定性（Centrifugal Interchange Instability）而被输运到离土星更远的地方.这种输运现象的发生是由离心力主导的,等离子体的黏滞效应和能量转移对输运过程的影响非常小（几乎可以忽略不计）,但土星电离层电导率对输运过程有重要影响,电导率越低,径向输运过程越快,反之,高电导率在一定程度上会阻碍输运的进行.在土星电离层电导率σ=2 S时,Dione（距离土星6.3R_S, R_S为土星半径）附近的等离子体在5.52个小时中被输运到距离土星10R_S的地方.本文的模拟结果还表明,密度受到扰动的等离子体是不稳定的,如果洛仑兹力和等离子体热压强梯度不能与离心力平衡,径向输运就会发生.密度大的等离子体在向外输运过程中会绝热膨胀而温度降低,密度小的等离子体则在注入磁层过程中因为绝热压缩而温度升高.     

Analysis of the Behavior of the Solar Wind Ion Flux in the Region of the Interplanetary Shock Overshoot

Geomagnetism and Aeronomy - The structure of the solar wind plasma flow downstream of the ramp of the interplanetary shock is studied based on the BMSW plasma spectrometer installed onboard the...     

空间尘埃等离子体电磁散射特性研究

基于尘埃等离子体Mie-Debye散射模型,研究平衡态下尘埃等离子体中带电尘埃的电磁散射特性.根据输运理论计算高层大气环境中尘埃等离子体层的电磁散射场,给出电磁波垂直入射时尘埃等离子体层的反射函数,同时分析不同浓度、不同粒径分布状态下尘埃等离子体层对电磁波传播的影响.结果表明:尘埃粒子尺度对其电磁散射特性影响非常大;在对数正态分布情况下,当入射波长远大于Debye半径时,尘埃等离子体的散射主要表现为Debye散射,而入射波长远小于Debye半径时,Mie散射占主要部分;并且尘埃等离子体层对电磁波的衰减随尘埃粒子浓度以及尘埃粒子半径的增大而明显增强.     

Time structure of the X-ray emission of thermal solar flares

Based on observations of electromagnetic radiation, a concept of thermal solar flares has been proposed. The absence of hard X-ray emission implies no accelerated electrons. This fact is the basis of the proposed concept of thermal flares. Since the acceleration rate should not exceed the electron energy loss rate, plasma density in the acceleration range must be at least 10¹¹ cm^?3. The temperature of plasma emitting in the soft X-ray range is of the order of 10⁷ K. In the simplified problem of heated plasma hydrodynamics, we calculated the temperature profiles and their changes over time and by coordinate. The emission measure values determined from observations of the soft X-ray emission of flares is of the order of 10⁴⁵ cm^?3. The geometry of the source is an axial symmetric straight cylinder with a section of 10¹⁶ cm² and an axial coordinate determined by the depth of plasma heating. Time profiles of soft X-ray emission were calculated for different sources of plasma heating, which were simulated using the Gaussian distribution law with respect to the coordinate and time. We have considered two modes of plasma heating: single (in time) and multipulse modes with different pulse intervals. The dynamics of plasma heating and cooling was shown to control the experimentally observed time profiles of soft X-ray emission. A comparison of numerical results with observational data allows us to confirm the implications of the proposed concept of thermal flares and, in addition, to perform diagnostics of plasma parameters in the emission source.     

Effects of spatial diffusion in the inner plasma sheet and the structure of the diffusion tensor

A standard pair of equations is used to describe the behaviour of a single monoenergetic particle (proton or electron) population on a geomagnetic flux tube drifting in the magnetosphere. When particle losses from the drifting flux tube into the ionosphere are neglected, this behaviour is adiabatic in a thermodynamic sense. For a population of particles with an isotropic pitch-angle distribution, the generalization of that system of equations is obtained by adding radial and azimuthal spatial diffusion terms. The magnetic field is taken to be dipolar in the inner magnetosphere. The potential electric field is assumed to consist of magnetospheric convection and corotation components. Experimental data are used to estimate the radial equatorial profiles of the plasma sheet pressure. Assuming that the local time and L-shell variations are separable and supposing steady-state conditions, the expressions for the diffusion tensor components are evaluated. The influence of spatial diffusion on the radial and azimuthal profiles of the plasma pressure in the inner plasma sheet is also discussed.     

Irregularities in unstable plasma of the upper atmosphere according to the data of sounding on board the Intercosmos-19 satellite

The profiles of the plasma density in the topside ionosphere, according to the data of sounding on board the Intercosmos-19 satellite, are presented. It is shown that the large-scale fluctuations of the plasma density can be related to the propagation and attenuation of the atmospheric waves (e.g., acoustic gravity waves) in the dynamo region of the ionosphere. In the topside ionosphere, suprathermal particle fluxes can be formed and the plasma density can be modulated at an attenuation of small-scale electrostatic fluctuations of the plasma electron component in plasma pits. Plasma vortices can be formed when polarization fluxes of charged particles escape from regions of heating. The vortex field imparts stability to the inhomogeneous plasma structure, necessary for experimental detection of this structure.     

Remotely imaging the plasma sheet with low-altitude satellite clusters

Low-altitude satellites make latitudinal cuts through the entire plasma sheet within a few minutes. We show that by combining several such satellites it is possible to form an image of a large portion of the plasma sheet within a relatively short time. Strictly speaking such a technique images the field-aligned portion of the plasma sheet, however, theoretical work as well as extensive in situ observations have demonstrated that the plasma sheet is highly isotropic. In practice the most significant limitation is that electron acceleration events (including the auroral bulge) require discarding the associated ion data. An instance when five DMSP satellites (F10–F14) went through the southern hemisphere nightside oval within a 19 min period is used to construct the first partial magnetotail image. The possibilities of combining data from other missions to construct more complete composite images is considered. This technique is also highly useful in statistical studies of the plasma sheet. Because a low-altitude spacecraft cuts through the plasma sheet about 25 times as often as a mid-altitude spacecraft, and hundreds of times more often than high-altitude spacecraft, statistically meaningful surveys of the plasma sheet as a whole are hundreds of times easier using a collection of DMSP satellites. We demonstrate herein that the dawn LLBL flank is an apparent source of cold magnetosheath plasma supplied to the central plasma sheet.     

Structure of the low-latitude magnetopause: MAGION-4 observations

The aims of this paper are (1) briefly to describe the plasma devices onboard the MAGION-4 satellite, launched on 3 August 1995, of the INTER-BALL project, and (2) to discuss first observations made near the magnetopause region. During the presented boundary crossings the MAGION–4 observed quasi-periodic pulses of magnetosheath-like plasma in a region of low plasma density. This region is located just earthwards of the magnetopause and is populated by a plasma which, except for the density, has the same parameters as in the magnetosheath. Deeper in the magnetosphere, the encounter of a layer of hot electrons and high-energy ions was interpreted as low-latitude boundary layer.     

Specific features of explosive plasma flows in the near-earth space

The analytical expressions for determining the deceleration region of plasma, produced during large-scale geophysical experiments of explosion type, and taking into account the effect of the rarefied ionosphere and geomagnetic field have been obtained. The possibility of the magnetosphere braking by plasma produced by a powerful explosion is analyzed. The simplified set of equations used to analyze the linear and non-linear stages of flute instability of explosive plasma expanding into the magnetic field has been obtained. The mass overflow between flutes and the viscous force is taken into account. The experimental studies of flute instability during laser plasma expansion into the magnetic field are theoretically substantiated. The mechanism explaining the formation of a jet stream and the main jet inclination of 11° with respect to the axis of symmetry has been proposed.     

Wave emission during a plasma density jump in the auroral zone of the topside ionosphere according to the APEX satellite data

The intensity of the wave emission in the 0.1–10 MHz band measured in the ionosphere (the APEX satellite experiment) has been presented. A jump of the plasma density and an increase in the emission intensity at a plasma frequency have been registered at altitudes of ～1300 km in the topside auroral ionosphere. The emission intensity in the whistler-mode band nonmonotonically increased along the satellite trajectory near the plasma jump wall. It has been indicated that waveguides could be formed near the wall during damping of electrostatic oscillations generated by precipitating electron fluxes. A spatially nonmonotonous separation of waveguides from the plasma inhomogeneity stretched along geomagnetic field lines is possible in this case.     

Effect of the charged dust grains on the neutral induced low frequency drift instability in a weakly ionized and magnetized dusty plasma

The role of neutrals in a partially ionized collisional dusty plasma is analyzed. In a magnetized inhomogeneous collisional dusty plasma, where plasma components have density gradients, neutrals can affect the instability significantly. Neutral induced instability and the effect of charge variation in such a dusty plasma are investigated. Dust size can control the neutral scale length which can answer the observed density irregularities in the ionosphere. Small sized dust particles favour damping due to charge variation while large sized particles assist collisional damping.