From the Solar Wind to the Magnetospheric Substorm

This paper gives a brief outline of the progression from the first substorm model developed in Ref.[4] and[8] based on Kennel's ideas[3], to the present views about the mechanism by which solar wind kinetic energy is converted to electromagnetic energy at the Bow Shock and by which this energy is transferred to the magnetosphere in the form of current; about the transformation of the energy of this current to gas kinetic energy of convecting plasma tubes, and, finally, the back transformation of gas kinetic energy to electromagnetic energy in secondary magnetospheric MHD generators. The questions of the formation of the magnetospheric convection system, the nature of substorm break-up, and of the matching of currents in the magnetosphere-ionosphere system are discussed.      

行星际激波对地球磁层的压缩效应分析

2004 年11月9日WIND飞船探测到一个典型的行星际激波. 激波前行星际磁场为持续约50 min的弱南向磁场, 越过激波面, 磁场发生北向偏转且太阳风动压脉冲增强. 在此强动压脉冲增强结构作用下, 磁层被压缩至一个很小的区域. 激波作用于磁层时引起地球同步轨道 各区域高能粒子通量的响应, 但是不同磁地方时的高能粒子通量的响应不同, 表现出双模式扰动, 即在晨昏两侧各能段的电子和质子通量显著增强, 在子夜侧发生类似于亚暴的无色散粒子注入现象. 扰动从向阳面传输到背阳面, 向阳面粒子通量最先增强, 随后背阳面靠近晨昏两侧, 粒子通量开始增强, 最后子夜侧粒子通量表现出无色散高能粒子注入的特点. 另外, 在靠近正午侧, 质子通量先于电子通量发生响应, 在子夜侧电子通量则先于质子通量发生响应. 利用位于向阳面正午两侧的GOES-10 和 GOES-12卫星观测数据发现, 激波作用于磁层时靠近晨侧的磁场变化表现出简单压缩效应, 而靠近昏侧的磁场变化则显然不同, Bx分量减弱, Bz分量几乎减为零, 而By分量则显著增强. 此外, 位于近地磁尾低纬尾瓣区的TC-1卫星观测到激波触发的尾瓣SI现象.      

太阳风向磁层输入电磁能量研究

利用全球磁流体力学（MHD）模拟结果,通过确立包含磁层顶的太阳风流线内边界来识别三维磁层顶位形,并以极尖区位置作为磁层顶日侧与夜侧的分界线,在此基础上定量研究了不同条件下穿过磁层顶向磁层内输入的电磁能量. 研究发现,磁层顶的能量传输与太阳风条件密切相关,磁重联是控制电磁能量传输的重要机制. 结果表明,当IMF（行星际磁场）南向时,极尖区后方的磁尾附近存在电磁能输入最大值,当IMF北向时,电磁能输入最大值发生在极尖区附近;南向IMF条件下,在IMF强度增大或太阳风密度增大时,磁层顶电磁能传输的电磁能量比北向IMF条件时增加更显著. 太阳风通过调节磁层顶面积间接影响到磁层顶能量传输大小. 研究还发现,北向IMF与南向IMF条件下穿过磁层顶的电磁能输入的比值范围约为10%～30%,此比值一定程度上反映了北、南方向IMF与地磁场磁重联效率的比值.      

Comparison of global MHD simulation results with actual storm and substorm events

Global MHD models hold the promise of providing a physics-based understanding of magnetospheric structure and dynamics. As such models have become more sophisticated, and computing power has increased, it is now possible to model actual events using solar wind data as a boundary condition. In this paper we present some results MHD simulations of actual storm and substorm events. We will demonstrate that not only can the simulations reproduce details of events, they also are reproducing fundamental aspects of energy coupling between the solar wind and the magnetosphere in such a manner that we can distinguish storms and substorms.     

ULF wave index as magnetospheric and space-weather parameters

Waves in the Ultra Low Frequency (ULF) band owe their existence to solar wind turbulence and transport momentum and energy from the solar wind to the magnetosphere and farther down. Therefore an index based on ULF wave power could better characterize solar wind–magnetosphere interaction than K_P, Dst, AE, etc. indices which described mainly quasi-study state condition of the system. We have shown that the ULF wave index accurately characterize relativistic electron dynamics in the magnetosphere as these waves are closely associated with circulation, diffusion and energization of relativistic electrons in the magnetosphere. High speed solar wind streams also act as a significant driver of activity in the Earth’s magnetosphere co-rotating interaction region and are responsible for geomagnetic activities. In the present paper, we have analyzed various cases related with very weak (quiet) days, weak days, storm days and eclipse events and discussed the utility of the ULF wave index to explain the magnetospheric dynamics and associated properties. We have tried to explain that the ULF wave index can equally be useful as a space weather parameter like the other indices.     

行星际磁场北向分量触发磁层扰动的可能性

本文用典型事件和统计分析论证了行星际磁场北向分量触发地磁扰动的可能性.给出了行星际电场E_y分量对磁层大尺度对流电场E_M的耦合系数.从耦合方程出发讨论了磁层对太阳风作用的响应,证明磁层不是起半波整流器作用,从而表明经典的重联理论应有所修改.      

Magnetospheric Boundary Layer Structure and Dynamics as Seen From Cluster and Double Star Measurements

In this review, we discuss the structure and dynamics of the magnetospheric Low-Latitude Boundary Layer (LLBL) based on recent results from multi-satellite missions Cluster and Double Star. This boundary layer, adjacent to the magnetopause on the magnetospheric side, usually consists of a mixture of plasma of magnetospheric and magnetosheath origins, and plays an important role in the transfer of mass and energy from the solar wind into the magnetosphere and subsequent magnetospheric dynamics. During southward Interplanetary Magnetic Field (IMF) conditions, this boundary layer is generally considered to be formed as a result of the reconnection process between the IMF and magnetospheric magnetic field lines at the dayside magnetopause, and the structure and plasma properties inside the LLBL can be understood in terms of the time history since the reconnection process. During northward IMF conditions, the LLBL is usually thicker, and has more complex structure and topology. Recent observations confirm that the LLBL observed at the dayside can be formed by single lobe reconnection, dual lobe reconnection, or by sequential dual lobe reconnection, as well as partially by localized cross-field diffusion. The LLBL magnetic topology and plasma signatures inside the different sub-layers formed by these processes are discussed in this review. The role of the Kelvin-Helmholtz instability in the formation of the LLBL at the flank magnetopause is also discussed. Overall, we conclude that the LLBL observed at the flanks can be formed by the combination of processes, (dual) lobe reconnection and plasma mixing due to non-linear Kelvin-Helmholtz waves.      

Sources and losses of ring current ions: An update

The cleft ion fountain has been identified as a prodigious source of upflowing suprathermal ionospheric plasma. Modeling efforts have traced the path of these ions from the polar ionosphere along trajectories where the ions are energized to keV energies and deposited in the near earth plasma sheet. Mass and energy dispersion of these ions accounts in a natural way for the observed variation in heavy ion content of the plasma sheet. Observations of ion composition in the plasma sheet by the AMPTE and ISEE spacecraft establish that ionospheric ions dominate in the near earth plasma sheet but solar wind ions become significant tailward. The heavy ion content of the plasma sheet increases with both solar cycle and magnetic activity. Direct injection of ionospheric ions into the ring current has been observed in the outer plasmasphere. Several mechanisms for the direct injection of ions from the plasmasphere and ionosphere into the ring current have appeared. Estimation of ionospheric source strengths and residence times have led to an estimate of the magnetospheric densities that would result solely from an ionospheric outflow populating the magnetosphere. Estimated densities were quite reasonable even without inclusion of a solar wind source of ions. Ring current ions decay primarily via charge exchange with the hydrogen geocorona, however, the roles of pitch angle diffusion and Coulomb collisions in this decay process are being clarified.

Modeling and observations of ENA by the 1SEE1 spacecraft has led to a re-affirmation of the dominant role of charge exchange in ring current decay. Ion cyclotron waves contribute to ring current decay in the dusk bulge region. The role of low frequency. (< 1 Hz) ion cyclotron waves in the plasmasphere is still unclear. Other wave modes may be responsible for the pitch angle diffusion and subsequent loss of ring current ions. Coulomb collisional energy losses from ring current O⁺ to thermal electrons are sufficient to power SAR arcs and represent an energy sink for ring current O⁺ within the plasmasphere. Coulomb collisions may be important for decay of low energy (< 10 KeV) ring current ions in the plasmasphere.     

Plasma convection model and generation of longitudinal currents in the earth's magnetosphere

The aim of this paper is to investigate processes in the magnetosphere and in particular the problems of the interaction of the solar wind with the Earth's magnetic field to produce large-scale convection, electric fields and longitudinal currents in the magnetosphere. The investigation is carried out in the frame of magnetic hydrodynamics. The reason for such an approach can be found in /1/. When calculating the transfer coefficients, the Böhm approximation is used, i.e. it is considered that the plasma in the near-equatorial part of the magnetosphere (quasiplanar geometry is used in the problem for simplification) is sufficiently turbulent that the condition ωτ ≈ 1 is valid (ω is the Larmor frequency of electrons, τ is effective time between two Quasi-collisions). The main subjects of investigation in this paper are the input near the equatorial boundary layer and the plasma layer of the magnetosphere tail.     

Circulation of energetic ions of terrestrial origin in the magnetosphere

Energetic ion composition measurements have now been performed from earth orbiting satellites for more than a decade. As early as 1972 we knew that energetic (keV) ions of terrestrial origin represented a non-negligible component of the storm time ring current. We have now assembled a significant body of knowledge concerning energetic ion composition throughout much of the earth's magnetosphere. We know that terrestrial ions are a common component of the hot equatorial magnetospheric plasma in the ring current and the plasma sheet out to ? 23 R_E. During periods of enhanced geomagnetic activity this component may become dominant. There is also clear evidence that the terrestrial component (specifically O⁺) is strongly dependent on solar cycle. Terrestrial ion source, transport, and acceleration regions have been identified in the polar auroral region, over the polar caps, in the magnetospheric boundary layers, and within the magnetotail lobes and plasma sheet boundary layer. Combining our present knowledge of these various magnetospheric ion populations, it is concluded that the primary terrestrial ion circulation pattern associated with enhanced geomagnetic activity involves direct injection from the auroral ion acceleration region into the plasma sheet boundary layer and central plasma sheet. The observed terrestrial component of the magnetospheric boundary layer and magnetotail lobes are inadequate to provide the required influx. They may, however, contribute significantly to the maintenence of the plasma sheet terrestrial ion population, particularly during periods of reduced geomagnetic activity. It is further concluded, on the basis of the relative energy distributions of H⁺ and O⁺ in the plasma sheet, that O⁺ probably contributes significantly to the ring current population at energies inaccessible to present ion composition instrumentation (? 30 keV).     

Theoretical aspects of heavy ion injections in the magnetosphere: A review

The theoretically expected effects of active heavy ion injections in the magnetosphere are reviewed according to their chemical state (plasma or neutral) and their kinetic state (explosion or beam injection) of release. The early-phase effects of such injections (such as ionospheric heating, wave-particle interactions, radiation belt and ring current modifications and anomalous ionization) are briefly discussed. The need for understanding the magnetospheric modification aspects of heavy ion injections becomes more acute in the next decades when the transportation and construction of large-scale space structures would inject increasing volumes of heavy ions in the magnetosphere by both chemical and ion engines. Ion engine exhaust, in the form of a dense relatively cool plasma beam of high drift speed, represents a new regime of heavy ion magnetospheric modification, the effects of which have not been thoroughly investigated either theoretically or observationally. We envisage that the ion engine can be modified into a useful tool for scientific studies of magnetospheric dynamics since it is a source of a variety of ionic species independent of the need for photoionization.     

Advanced techniques for plasma composition and dynamics measurements

Magnetic and RF mass spectrometers have been used routinely in ionospheric research, while traditional ionospheric, magnetospheric, and interplanetary plasma measurements have been made with several types of electrostatic analyzers. Proper interpretation of these data is possible if the spectral peaks are well defined, although ambiguities between fast, light ions and slow, heavy ions cannot always be satisfactorily resolved. Recent and planned experiments involve the study of plasmas which are sufficiently energetic that the spectral peaks overlap. Furthermore, these studies of ionosphere/magnetosphere coupling and of the interaction of the solar wind with the atmospheres of Venus and comets require unambiguous identification of the ion masses with simultaneous mapping of the three-dimensional velocity distribution function of each ion species. This challenge has been partially met by several new types of instruments; the two most common types involve either (1) sequential electrostatic and magnetic analyses or (2) sequential electrostatic and time-of-flight analyses. Some new instruments have also incorporated measurements of total kinetic energy, electric charge, or secondary emission coefficients as diagnostic tools. This paper reviews these recent advances and points out areas where further development is expected and needed.     

三维试验粒子轨道法在磁层粒子全球输运中的应用

根据磁层粒子动力学理论, 通过偶极磁场模型验证利用三维试验粒子轨道方法模拟近地球区(r < 8R_e)带电粒子运动特征的可靠性. 在此基础上, 以太阳风和磁层相互作用的全球MHD模拟结果为背景, 利用三维试验粒子轨道方法, 对非磁暴期间南向行星际磁场背景下太阳风离子注入磁层的情形进行数值模拟, 并对北向行星际磁场背景下太阳风离子注入极尖区以及内磁层的几种不同情形进行了单粒子模拟. 模拟结果反映了南向和北向行星际磁场离子向磁层的几种典型输入过程, 揭示出行星际磁场南向时太阳风粒子在磁层内密度分布的晨昏不对称性以及其在磁鞘和磁层内的大致分布, 并得出统计规律. 模拟结果与理论预测和观测结论相一致, 且通过数值模拟发现, 行星际磁场北向时靠近极尖区附近形成的非典型磁镜结构对于能量粒子经由极尖区注入环电流区域过程有重要的影响和作用.      

行星际起伏向磁层顶的输运

时间尺度为分钟数量级的太阳风速度和行星际磁场大幅度扰动实际上始终存在于行星际空间的。这些扰动一直传输到紧贴磁层边界面外侧的区域。它们在磁鞘等离子体和磁层顶的相互作用过程中可能起很重要的作用。行星际起伏中的磁场分量在通过地球弓激波时首先经历一次跳跃,然后一部分扰动被带到磁层边界面处。在边界面附近磁场扰动幅度被大大地放大了。弓激波上游的太阳风条件控制了放大因子。本文所作的数值模拟研究结果表明,如果上游有大幅度的扰动,在边界面附近就有大幅度的Alfven起伏的磁场分量。当上游磁场接近垂直于日地联线时,放大因子变得相当大,而且放大因子随上游的等离子体β值和/或Alfven马赫数的增加而增加。上游各向异性对放大因子的影响不大。在磁层边界附近存在大幅度起伏表明这里不存在稳定的片流。      

The thermosphere as a sink of magnetospheric energy: A review of recent observations of dynamics

The study of the dynamics and thermodynamics of the earth's upper atmosphere has made significant progress over the past few years owing to the availability of new global-scale data sets from the Dynamics Explorer satellites. The thermospheric wind and temperature fields at high latitude have been observed to depend strongly on forcing processes of magnetospheric origin. A key momentum source is due to the drag effect of ions convecting in response to electric fields mapped down on the ionosphere from magnetospheric boundary regions. Likewise, an important heat source derives from Joule or frictional dissipation due to ion/neutral difference velocities governed, in turn, by magnetospheric forcing. In this paper we discuss the progress made over the last 2–3 years initiated by the new satellite measurements and we review published data on ion and neutral motions in the context of the energy and momentum coupling between the magnetosphere and the ionosphere/neutral upper atmosphere. The observations indicate the existence of a “flywheel effect” which implies direct feedback from the neutral thermosphere to the magnetosphere via the release of energy and momentum previously “stored” in the neutral thermosphere.     

Is the poleward edge of the trough a sensitive indicator of geospace interactions?

The poleward edge of the main ionospheric trough can often be regarded as the ionospheric signature of the equatorward boundary of the plasma sheet. We use Advanced Ionospheric Sounder observations of the poleward edge from Halley, Antarctica (76°S, 27°W; L=4.2) to investigate some aspects of its dynamics with respect to changes of magnetospheric and solar wind conditions. We find that there is frequently rapid equatorward motion of the poleward edge from ∼20 minutes before to ∼30 minutes after the onset of the main phase of a substorm. These observations are discussed in terms of the dynamics of the plasma sheet during substorm activity. Another class of rapid equatorward motion of the poleward edge of the trough has no apparent cause in the magnetosphere or solar wind. Possible explanations involving longitudinal structure of the trough or small-scale structure of the solar wind are considered.     

Stability and mass flow in Saturn's rings

Besides gravitational effects, interesting electrodynamical processes could also take place in the vicinity of the rings of Saturn. In part, this is because of the electrostatic charging of the ring particles by the magnetospheric and ionospheric plasma, and in part, the generation of impact plasma by meteoroid bombardment at the ring plane could lead to strong coupling between the rings and the ionosphere via a variety of current systems. The mass transport and angular momentum transfer in association with the ring-ionosphere coupling may cause quite large changes in the ring configuration over the age of the solar system. The presence of the sharp boundary between the B and the C rings perhaps is a good example. To highlight these new developments, we describe several of the electrodynamical mechanisms (with emphasis on their corresponding electric fields and current systems) which have been postulated to be of importance in determining the mass transport of the ring system. Further points are made that, besides mass exchange between the rings and the planetary atmosphere, the mass injection from the rings could also have significant effect on the mass and energy budget of the magnetosphere, maintenance of the E ring, the Titan hydrogen torus as well as aeronomic process in the upper atmosphere of Titan.     

磁层顶低混杂漂移不稳定性及等离子体幔、磁层对流的形成机制

磁层顶低混杂漂移不稳定性的理论和观测使我们可以提出一个新的磁层对流驱动模式,为了解释磁层对流的形成、磁层顶厚度等一系列磁层现象,已经提出了三种磁层模式,Dunge提出互联模式,认为行星际磁场磁力线与地磁场磁力线在磁层顶前部相互联接起来,磁层顶为一旋转间断面,太阳风粒子可直接通过磁层顶进入磁层内,虽然这一     

Spatial distribution of the magnetosheath ion flux

The magnetosheath plays a crucial role in solar wind-magnetosphere interaction because it is the magnetosheath magnetic field and plasma that interact with the magnetopause and magnetosphere, not the unshocked solar wind. We are presenting ion flux measurement statistics at both the dawn and dusk flanks of the magnetosheath and their comparison with a gasdynamic magnetosheath model. The study is based on three years of INTERBALL-1 measurements supported by simultaneous WIND solar wind and magnetic field observations. Statistical processing has shown (1) the limitations of the gasdynamic model, (2) the conditions favorable for the creation of a plasma depletion layer adjacent to the flank magnetopause, (3) strong dawn-dusk asymmetry of the ion fluxes, and (4) an evidence for the presence of a slow mode front adjacent to the magnetopause.     

Laboratory experiments and space phenomena

Two types of convection were observed in the laboratory model of the magnetosphere: viscous convection and convection due to field lines common to both the magnetosphere and artificial solar wind. With a southward field component in the solar wind, convection from the Sun is observed in the polar cap, while with a large northward component, convection is directed toward the Sun. Merging of the field lines occurs in the cleft. With the southward component, a visor appears in front of the magnetosphere boundary. The decay of the visor into small magnetic structure is observed. The formation of an induced magnetosphere with a magnetic tail is shown in the experiments of the simulated conditions near non-magnetic bodies with a plasma shell (Venus, comets). A combined induced-intrinsic magnetosphere also was investigated.