用数值模拟的方法研究磁暴主相期间影响环电流分布特征的要素

环电流是距离地心2～7 Re的带电粒子围绕地球西向漂移形成的.环电流的增强将引起全球磁场的降低,反映了地磁暴的强度.磁暴主相期间,对流电场驱动等离子体片中的能量粒子经历E×B漂移与俘获注入环电流,进入损失锥的粒子沉降到大气中.本文采用磁暴主相期间环电流离子分布的模型,结合上述因素研究不同离子能量下对流电场对环电流离子通量的直接影响,以及强弱对流电场下环电流能量离子投掷角的变化,并从物理上阐述造成此种通量分布特性的原因.      

Detection of suprathermal ionospheric O+ ions inside the plasmasphere

The plasma diagnostic experiments on the AUREOL-3 satellite have revealed flows of low energy 0⁺ ions deep inside the night plasmasphere during a large substorm. Flux gradients of the 0⁺ ions were accompanied by enhancements of ELF electric field noise. The appearance of suprathermal ions at $\text{L ? 2.5 – 3}$ is interpreted within the framework of electrostatic ion-cyclotron acceleration of ionospheric ions in the diffuse auroral zone /12/ followed by a radial displacement of these ions inside the plasmasphere driven by azimuthal electric fields during substorm activity. Electrostatic oscillations observed inside the plasmasphere are apparently associated with gradient instability at the sharp boundaries of suprathermal ion flows.     

Do ring current ions set the outer plasmasphere in motion?

GEOS-2 experiments have observed on a regular basis the transition from teh plasmasphere to the trough revealing a more tenuous and energetic population. This transition occured typically between 18 and 21 h local time under quiet geomagnetic conditions. On the plasmasphere side of the transition, large electric fields of several mV/m, mainly in the duskward direction, were observed. The present statistical results, over one year of data, assess clearly the mean magnitude and direction of these electric fields in relation to the boundary between these two plasma regimes under quiet geomagnetic conditions. The possibility of ring current energetic ions loosing part of their energy to the plasmasphere and accelerating this plasma sunward will be discussed.     

Dynamic trapping of electrons in the porcupine ionospheric ion beam experiment

Electrons are needed to maintain quasineutrality in a case where positive ions are injected across the magnetic field into a limited volume in a magnetized plasma. In the absence of collisions, a positive potential builds up and traps the electrons which enter the region along the magnetic field. If the added density of ions exceeds the ambient density, large potential differences along the magnetic field can be maintained this way. The process explains several features of the Porcupine xenon ion beam injection experiment, where strong magnetic-field-aligned electric fields were measured in the vicinity of a xenon ion beam which was injected into the ambient ionosphere from a spinning subpayload.     

Interaction of artificially injected plasma flows with ionospheric plasma

Results of rocket experiments on study of plasma flows (PF) artificially injected by sources separated from vehicles and their effect on medium parameters in ionosphere at altitudes 160:230 km are presented.PF were injected comprising lithium ions with velocities 1,2 x 10⁴ m/sec. and cesium-potassium ions with velocities (1,4–1,5)x10³ m/sec. Mass flow rate in case of lithium PS is 2 mg/sec, and in case of cesium-potassium PS is 0,2 g/sec. During experiments mass-spectrometer measurements of ion medium content in ranges of different ion masses were held, disturbancies of electric fields with frequencies up to 20 kHz and electron flows with energies 0,7keV, 4,6keV and over 40 keV were controlled at distancies from 150m to (500–600)m between plasma source and scientific equipment.     

卫星介质深层充电中的主要物理问题

卫星介质深层充电效应是诱发地球同步轨道卫星运行故障和异常的重要因素之一，通过计算机模拟对介质深层充电的时间常数、电场特征、以及屏蔽、介质厚度和接地方式对充电所致最大电场的影响等主要物理问题进行了详细的分析，并给出了初步的防护措施．     

卫星介质深层充电的两类计算模型对比分析

计算模拟是评估航天器介质深层充电危害的重要研究方法之一. 通过粒子输运 模拟, 可以得到特定空间辐射环境下介质中的电荷沉积分布, 进而根据电位/电 场计算模型, 得到深层充电结果. 前期研究多是围绕RIC (辐射诱导电导率)模 型及其改进模型展开的, 而目前通常采用基于电流守恒定律的简单计算模型. 为了研究二者关系, 给出其各自求解方法, 并采用已发表数据对计算结果进行 验证; 从理论上阐述了后者是RIC模型的进一步简化, 只要二者考虑相同的介 质电导率, 则对应计算结果就是一致的; 结合GEO恶劣电子辐射环境下平板介 质模型在三类边界条件下的充电情况, 进行了充分的仿真验证. 相关结论为介 质深层充电效应评估提供了有益参考.      

环电流区能量离子分布特性研究

为了考察环电流区离子的分布情况,采用环电流粒子理论模式,对环电流中10-100 keV的离子进行了模拟研究.这个模式能够根据近地注入区外边界处离子的分布函数得出磁暴主相期间环电流中的主要成分H+,O+,He+3种离子的通量分布.计算结果分析表明,在其他条件相同的情况下,不同种类离子的通量分布的形态结构十分相似.电场强度对环电流离子通量的空间分布具有决定性的作用;晨昏电场强度越强,离子的通量越高;晨昏电场越强,环电流离子的内边界越接近地球.10keV的离子在电场相当弱的时候还是存在着连续的通量分布,但他们的形态和结构随着电场的变化有明显的变化.电场很弱时,离子分布主要集中于内外两个环带,离子通量在晨侧的更多一些,离子通量的最大值基本上是在比较靠近地球的环带上;随着电场的增强,离子分布的内外两个环带逐步合并,离子的分布逐渐靠近地球,通量分布的最大值也移动到了昏侧.环电流离子投掷角分布具有各向异性,投掷角在90°左右的时候,离子通量能达到最大值.      

Active stimulation of the ionospheric plasma

Laboratory experiments in which high power, pulsed electromagnetic waves interact with an inhomogeneous plasma indicate that the generated nonlinear plasma phenomena depend on peak incident power and not on pulse length. The electromagnetic waves can penetrate beyond the cutoff and produce large, enhanced electrostatic fields at the critical layer within 100 electron plasma periods. The enhanced electric field pressure can be comparable to the thermal pressure and can accelerate ions and electrons to velocities much greater than their thermal speed. Large density cavities (with δn/n ? 10%) can be created in a time shorter than the usual ion response time because of the accelerated ion dynamics. These laboratory results have been extended to create a new and generalized concept to actively stimulate space plasmas with high power pulses of short duration. A field experiment will be used for the stimulation of auroral ionospheric plasma. The ground-based system is modular, each module consisting of a 2 MW pulsed HF transmitter designed at UCLA and a crossed-dipole antenna element. Incoherent scatter radar and optical diagnostic methods are discussed.     

Equatorial ionosphere–thermosphere system: Electrodynamics and irregularities

The equatorial ionosphere and thermosphere constitute a coupled system, with its electro dynamical and plasma physical processes being responsible for a variety of ionospheric phenomena peculiar to the equatorial region. The most important of these phenomena are: the equatorial electrojet (EEJ) current system and its instabilities, the equatorial ionization anomaly (EIA), and the plasma instabilities/irregularities of the night ionosphere (associated with the plasma bubble events – ESF). They constitute the major topics of investigations having both scientific and practical objectives. The tidal wind interaction with the geomagnetic field is responsible for the atmospheric dynamo electric fields, that together with the wind system, drives the major phenomena, under quiet conditions. Drastic modifications of these phenomena can occur due to magnetospheric forcing under solar-, interplanetary- and magnetospheric disturbances. They can also undergo significant modifications due to forcing by atmospheric waves (such as planetary- and atmospheric gravity waves) propagating upward or from extra tropics. This article will focus on the ambient conditions of the ionosphere–thermosphere system and the electro dynamics and plasma instability processes that govern the plasma irregularity generation. Major emphasis is given to problems related to the structuring of the equatorial night ionosphere through plasma bubble/ESF irregularity processes. Specific topics to be covered will include: equatorial electric fields, thermospheric winds, sunset electrodynamic processes, plasma drifts, EEJ plasma instability/irregularity generation, nighttime/post sunset plasma bubble irregularity generation, and very briefly, disturbance electric fields and winds and their effect on the ionization anomaly, the TEC and ESF/plasma bubble irregularities.     

The collective gyration of a heavy ion cloud in a magnetized plasma

In both the ionospheric barium injection experiments CRIT I and CRIT II, a long-duration oscillation was seen with a frequency close to the gyro frequency of barium and a time duration of about one second. A model for the phenomenon which was proposed for the CRIT 1 experiment is here compared to the results from CRIT II which made a much more complete set of measurements. The model follows the motion of a low-β ion cloud through a larger ambient plasma. The internal field of the model is close to antiparallel to the injection direction v_i but slightly tilted towards the self-polarization direction E_P = −v_ixB. As the ions move across the magnetic field, the space charge is continuously neutralized by magnetic-field aligned electron currents from the ambient ionosphere, drawn by the divergence in the perpendicular electric field. These currents give a perturbation of the magnetic field related to the electric field perturbation by ΔE/ΔB ≈ V_a. The model predictions agree quite well with the observed vector directions, field strengths, and decay times of the electric and magnetic fields in CRIT II. The possibility to extend the model to the active region, where the ions are produced in this type of self-ionizing injection experiments, is discussed.     

On high-altitude electric fields in the auroral downward current region and their coupling to ionospheric electric fields

The downward field-aligned current region plays an active role in magnetosphere–ionosphere coupling processes associated with aurora. A quasi-static electric field structure with a downward parallel electric field forms at altitudes between 800 km and 5000 km, accelerating ionospheric electrons upward, away from the auroral ionosphere. Other phenomena including energetic ion conics, electron solitary waves, low-frequency wave activity, and plasma density cavities occur in this region, which also acts as a source region for VLF saucers. Results are presented from high-altitude Cluster observations with particular emphasis on the characteristics and dynamics of quasi-static electric field structures. These, extending up to altitudes of at least 4–5 Earth radii, appear commonly as monopolar or bipolar electric fields. The former occur at sharp boundaries, such as the polar cap boundary whereas the bipolar fields occur at softer boundaries within the plasma sheet. The temporal evolution of quasi-static electric field structures, as captured by the pearls-on-a-string configuration of the Cluster spacecraft, indicates that the formation of electric field structures and of ionospheric plasma density cavities are closely coupled processes. A related feature of the downward current is a broadening of the current sheet with time, possibly related to the depletion process. Preliminary studies of the coupling of electric fields in the downward current region, show that small-scale structures are typically decoupled from the ionosphere, similar to what has been found for the upward current region. However, exceptions are also found where small-scale electric fields couple perfectly between the ionosphere and Cluster altitudes. Recent FAST results indicate that the degree of coupling differs between sheet-like and curved structures, and that it is typically partial. The electric field coupling further depends on the current–voltage relationship, which is highly non-linear in the downward current region, and still unrevealed, as to its specific form.     

Kinetic theory of the current sheath. I. On polarization of an equilibrium current sheath

The basic theme of this paper is the investigation of the polarizing electric fields caused by anisotropy of thermal plasma of a current sheath. The paper provides a generalization of the equilibrium distribution function of the current sheath (Harris function) to the case of temperature anisotropy of plasma along and across the sheath. It appears that solution of the electroneutral equilibrium represents a narrow class of solutions and is true only for certain relations between the parameters of the problem. In the general case, the plasma of a stationary current sheath is polarized. The structure of the current sheath of a magnetosphere tail is investigated with regard to the effect of polarization, and profiles of the polarization electric fields are obtained. This field should be taken into account in the study of current sheath stability.     

A one-dimensional model of DC electric field generation at neutral gas release experiments

Electromagnetic aspects of the coupling between plasma produced from a moving neutral gas cloud and a magnetized background plasma is studied on the basis of a one-dimensional plasma model. Two sources of electric DC fields are isolated and the spatial field structure is calculated under different conditions.     

热流效应对场向电流确定的影响

给出了任意速度分布函数条件下复频率的介电函数和色散关系的求解方法. 讨论了16矩近似条件下, 场向热流对电子速度分布函数, 介电函数实部与虚部, 以及离子与电子谐振频率和阻尼率的影响, 并与平衡态时麦克斯韦分布等离子体的计算结果进行了比较. 忽略场向热流效应, 正向电子漂移速度条件下, 上行等离子线探测, 会过高估计场向电流; 负向电子漂移速度条件下, 上行等离子线探测会过低估计场向电流. 对上下行等离子线同时探测情况, 忽略热流效应同样会过高估计场向电流.      

A Simulation of the Mid-and Low-latitude Ionospheric Electric Fields

A theoretical model of ionospheric electric fields at mid- and low-latitudes is developed. In the geomagnetic dipolar coordinate system, the ionospheric dynamo equations were solved, and the ionospheric electric potential and electric field were derived respectively. Major parameters for the model inputs, such as the neutral winds, the densities and temperatures of electron, ions and neutrals, are obtained from empirical models. The global ionospheric electrical potential and field at mid- and low-latitudes derived from our model are largely in agreement with the results presented by other authors and the empirical model. Using our model, it is found that the diurnal component of the HWM93 wind mainly contributed to the formation of the vertical electric field, while the semidiurnal component mainly contributed to the zonal electric field. Finally, by adjustment of the input F region winds and conductivities, most discrepancies between our model and the empirical one can be eliminated, and it is proved that the F region dynamo is the most significant contribution to the electric fields.      

Calculating the simultaneous effect of ion dynamics and oscillating electric fields on Stark profiles

We calculate hydrogen line shapes resulting from the simultaneous Stark effect of the plasma microfield and an oscillating electric field. Like laboratory plasmas, many kinds of space plasmas are affected by oscillating electric fields with a magnitude similar to that of the microfield. Here we focus on conditions where we expect that the effect of ion dynamics and oscillating electric are both significant. The combined effect of their dynamics on the quantum emitter is retained by a computer simulation coupled to a numerical integration of the Schrödinger equation. Our calculations are applied for conditions and transitions where significant changes in the line shape allow for a diagnostic of the plasma and oscillating field.     

Electron acoustic solitary waves in the Earth’s magnetotail region

Satellite observations have revealed solitary potential structures in the Earth’s magnetotail region. These structures have both positive (compressive) and negative (rarefactive) electrostatic potentials. In this paper we study the electron-acoustic solitary waves (EASWs) in an unmagnetized plasma consisting of cold plasma electrons and isothermal ions with two different temperatures. Using the reductive perturbation method, the nonlinear evolution of such structures is studied. The numerical computations are performed to study the role of two temperature ions in the generation of EASWs. In this case, the model supports the existence of both positive and negative electrostatic potentials with bipolar pulses. The electric field associated with these positive and negative solitary structures are numerically computed. The present study could be useful to construe the compressive and rarefactive electric field bipolar pulses associated with the BEN type emissions in the magnetospheric regions where the electron beams are not present.     

Global characteristics of ionospheric electric fields and disturbances during the first hours of magnetic storms

The ionospheric plasma density can be significantly disturbed during magnetic storms. In the conventional scenario of ionospheric storms, the negative storm phases with plasma density decreases are caused by neutral composition changes, and the positive storm phases with plasma density increases are often related to atmospheric gravity waves. However, recent studies show that the global redistribution of the ionospheric plasma is dominated primarily by electric fields during the first hours of magnetic storms. In this paper, we present the measurements of ionospheric disturbances by the DMSP satellites and GPS network during the magnetic storm on 6 April 2000. The DMSP measurements include the F region ion velocity and density at the altitude of ∼840 km, and the GPS receiver network provides total electron content (TEC) measurements. The storm-time ionospheric disturbances show the following characteristics. The plasma density is deeply depleted in a latitudinal range of ∼20° over the equatorial region in the evening sector, and the depletions represent plasma bubbles. The ionospheric plasma density at middle latitudes (20°–40° magnetic latitudes) is significantly increased. The dayside TEC is increased simultaneously over a large latitudinal range. An enhanced TEC band forms in the afternoon sector, goes through the cusp region, and enters the polar cap. All the observed ionospheric disturbances occur within 1–5 h from the storm sudden commencement. The observations suggest that penetration electric fields play a major role in the rapid generation of equatorial plasma bubbles and the simultaneous increases of the dayside TEC within the first 2 h during the storm main phase. The ionospheric disturbances at later times may be caused by the combination of penetration electric fields and neutral wind dynamo process.     

有涂覆层的导体圆柱空间散射特性的数值计算

文中根据带有涂覆层的导体圆柱在平面波的照射下的散射场表达式,进行了全面的数值计算,说明了虚宗量的Bessel函数和Hankel函数的计算方法,分别给出了平行极化波和垂直极化波入射时双站RCS的计算曲线,包括不同涂覆层厚度的影响、入射波频率、涂覆层介质的相对介电常数、导磁率变化时双站RCS的变化规律,获得了有参考意义的结果.