等离子体片边界层电磁不稳定性引起的波－粒输运

采用二级理论研究了在等离子体片边界层电磁不稳定性引起的波—粒输运．结果表明，束流离子被热化和各向同性化，离子最大加热率峰值与电磁不稳定性最大增长率峰值出现在大致相同的方向上．被热化和各向同性化的束流离子可能是等离子体片中心区热离子的来源．这些结果对于理解等离子体片边界层的输运过程具有重要的意义．     

中高度极隙区电磁不稳定性

研究了中高度（离地心３－４个地球半径）极隙区上行电子束流和上行氧离子（ｏ^＋）锥引起的沿磁力线传播的电磁不稳定性．采用的物理模型假定：上行电子具有单能束流分布函数，而上行氧离子（ｏ^＋）锥可用单能环－束分布函数来描述．结果表明，左旋和右旋圆偏振的低频电磁模是不稳定的，激发不稳定性的自由能源主要由上行电子束流提供，而上行氧离子（ｏ^＋）锥因自由能太小只影响频率色散关系，上行粒子（电子和氧离子）与背景等离子体密度比的变化对电磁不稳定性有重要影响．这些结果对解释权隙区纬度地面站低频电磁波观测资料和理解极隙区动力学过程是很有益的．     

磁尾宽频带静电噪声的一种新的激发机制

本文提出了磁尾宽频带静电噪声强谱段的一种新的激发机制。在等离子体片边界层中存在着瞬时的局域性的晨昏电场。电子和离子对该电场的响应不同:在电场存在的区域内,电子作回旋漂移运动,而离子轨道在的时间尺度内可视为直线。由于等离子体片边界层中等离子体是非均匀的,这就导致了电荷分离的产生,从而可激发静电不稳定性。本文通过求解含电场的Vlasov方程,计算了由此产生的不稳定波的频率和增长率,考察了波矢方向。上述计算结果均与强谱段静电噪声的观测特征一致。     

磁尾等离子体片区氧离子丰度对离子剪切流的开尔文-赫姆霍茨不稳定性的影响

考虑等离子体片区存在源于电离层的氧离子,研究了离子剪切流在低频表面波扰动情况下的开尔文-赫姆霍茨(K-H)不稳定性.在氧离子流与质子流具有近似相同的宏观流速假定下,采用磁流体力学(MHD)近似,并且考虑在磁场方程中保留速度场涡量项,推导出沿磁场方向传播的表面波线性扰动的色散关系.在等离子体片边界层区,发现随着氧离子相对丰度的增加,产生K-H不稳定性的最大临界扰动波长可增大到20RE(地球半径).对于给定的氧离子丰度,临界剪切相对扰动波长的变化存在一个最小值.氧离子丰度越高,最小临界剪切值越小,对应的扰动波长(称最不稳定波长)也越长.高氧离子丰度的不稳定性增长率随速度剪切增加而增加,快于低氧离子丰度.不稳定性增长率随速度剪切增加的最大饱和值接近对应的离子回旋频率.在地磁活动期间,由等离子体片中氧离子丰度增加而增大的沿磁场传播的表面波不稳定性对于理解低频磁脉动事件和磁层亚暴过程也有着十分重要的意义.     

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．     

K-H不稳定性在多电流片系统磁场重联中的效应

等离子体系统中存在两个或多个电流片时，电流片中发生的不稳定性可能会相互作用．行星际磁场北向时，背阳面碰层顶电流片与磁尾等离子体片之间可能发生相互作用，高纬边界层强烈的流场剪切可能促进磁场重联，产生磁层亚暴．本文运用二维可压缩磁流体模拟研究具有强流场剪切的多个电流片系统中磁场重联的演化．结果表明，Kelvin－Helmholtz不稳定性使多电流片系统的磁场重联过程明显加快；相邻电流片之间的距离越近，两者相互作用越强，重联增长率越大；在三电流片系统中，超Alfven速度强流场导致外侧两个电流片中出现强烈的磁场重联，并引发中心电流片的磁场重联．行星际磁场北向时，也可能发生磁层亚暴．     

近磁尾TC-1观测到伴随有高速流的ULF波及不稳定性分析

2004年8月3日近地TC-1卫星在磁尾X_GSM~－12R_E的等离子体片内,观测到了伴随着高速流的低于离子回旋频率的波,即超低频波(ULF,Ultra Low Frequency).该波垂直分量的振幅在高速流及其振荡减速期间大致相当;而平行分量振幅在高速流时明显大于其振荡减速时. 利用一个扰动双流模型对完全磁化离子横场漂移驱动的电磁不稳定性计算后,预测结果表明:(1)对于垂直分量来说,横场漂移速度与Alfvén速度的比值影响不稳定性增长率和激发波频率,随其比值增加,增长率变大,激发波频率从负值增加到正值.(2)对于平行分量来说,温度各向异性时等离子体热速度与Alfvén速度比值只影响不稳定性增长率和激发波频率,未改变不稳定性模类别;而温度各向同性时离子横场漂移速度与Alfvén速度比值既影响不稳定性模的种类及其分支,又影响激发波频率.进一步将卫星观测到的等离子体密度、温度、整体流速和磁场代入模型方程,进行数值计算与上述预测结果对比后发现:卫星观测中垂直分量的功率谱密度(PSD,Power Spectrum Density)增强时间和频段与理论模型中由β_//、β_⊥和v_⊥/V_A引起不稳定性激发的波一致;卫星观测中平行分量的功率谱密度增强时间与理论模型基本相符,但是前者的频率明显地低于后者.因此,除了需考虑平行磁场的离子整体流速对不稳定性激发波频率的可能影响,还需要统计上进一步核实伴随有高速流的ULF波与不稳定性的相关性.     

等离子体片边界层内静电离子束流-密度漂移不稳定性

本文研究了地球磁尾等离子体片边界层内由离子束流和等离子体密度梯度联合作用产生的静电不稳定性.模型等离子体由向尾流动的冷离子束流、向地球流动的暖离子束流和背景暖电子组成,等离子体密度是非均匀的,等离子体β（热压强与磁压强之比值）很小,电子等离子体频率与电子退旋频率之比。ω_e/Ω_e》1.结果表明,斜传播的静电快、慢离子束流-密度漂移模能够被激发。     

引力场中磁场重联的数值研究（Ⅲ）等离子体团的形成和运动

应用解析和数值相结合的方法求得了含有闭场区、中性片和开场区的二维局域磁静力平衡日冕基态，进而在此基态下数值研究了由电阻撕裂模不稳定性引起的磁场重联过程．结果表明，在电流片长度远大于其半宽度的情况下，仍将发生具有两个Ｘ线的磁场重联，形成磁岛和高温高密度的等离子体团．等离子体团运动的方向取决于闭合区底部等离子体压力和磁压的比值β０．当β０较大时，等离子体团向下运动，引起结合不稳定性和磁岛的合并，等离子体团中的等离子体不断落入闭合磁场区两侧．当β０较小时，等离子体团向上运动，导致电流片中等离子体的喷发．结果还表明，磁张力的分布是决定等离子体团运动方向的主要因子．     

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.     

Electromagnetic induction in spherical cap current layers under lunar and terrestrial conditions

We present the theory of electromagnetic induction in spherical cap current sheets of arbitrary angular size, with arbitrary axisymmetric integrated electrical conductivity variations and located at any radial position with respect to the surface of observation. The external time-varying magnetic field may be arbitrarily oriented with respect to the current layer cap and the induced fields are derived for vacuum boundary conditions appropriate to terrestrial induction and plasma confinement boundary conditions relevant to lunar induction in the solar wind or magnetosheath plasmas. Numerical evaluations show the induced magnetic field as a function of position over the current sheet cap, depth to the current layer, size of the cap, integrated electrical conductivity of the current sheet, and frequency of the fluctuating external field. The local vertical magnetic field component and the horizontal field component which is normal to the periphery of the cap exhibit peak inductive responses above the edge of the current sheet for external magnetic fields perpendicular to the axis of the cap. Thus, induced magnetic field fluctuations observed over the edge of a conductivity anomaly may exhibit a highly directional, or polarized behavior. This may provide an explanation for the asymmetric character of induced magnetic field fluctuations observed on the lunar surface.     

Spatial structure of the plasma sheet boundary layer at distances greater than 180 RE as derived from energetic particle measurements on GEOTAIL

We have analyzed the onsets of energetic particle bursts detected by the ICS and STICS sensors of the EPIC instrument on board the GEOTAIL spacecraft in the deep magnetotail (i.e., at distances greater than 180 RK). Such bursts are commonly observed at the plasma-sheet boundary layer (PSBL) and are highly collimated along the magnetic field. The bursts display a normal velocity dispersion (i.e., the higher-speed particles are seen first, while the progressively lower speed particles are seen later) when observed upon entry of the spacecraft from the magnetotail lobes into the plasma sheet. Upon exit from the plasma sheet a reverse velocity dispersion is observed (i.e., lower-speed particles disappear first and higher-speed particles disappear last). Three major findings are as follows. First, the tailward-jetting energetic particle populations of the distant-tail plasma sheet display an energy layering: the energetic electrons stream along open PSBL field lines with peak fluxes at the lobes. Energetic protons occupy the next layer, and as the spacecraft moves towards the neutral sheet progressively decreasing energies are encountered systematically. These plasma-sheet layers display spatial symmetry, with the plane of symmetry the neutral sheet. Second, if we consider the same energy level of energetic particles, then the H layer is confined within that of the energetic electron, the He⁺⁺ layer is confined within that of the proton, and the oxygen layer is confined within the alpha particle layer. Third, whenever the energetic electrons show higher fluxes inside the plasma sheet as compared to those at the boundary layer, their angular distribution is isotropic irrespective of the Earthward or tailward character of fluxes, suggesting a closed field line topology.     

General velocity formula of boundary layer above mobile sediment bed induced by asymmetric waves

Sediment movement in the wave boundary layer above a mobile sediment bed is complex.A velocity formula for the boundary layer is proposed for sheet flow induced by asymmetric waves above a mobile sediment bed.The formula consists of a free stream velocity and a defect function which contains a phase-lead,boundary layer thickness and mobile sediment bed.Phase-lag of sediment movement is considered in the formula for the mobile sediment bed.The formula needs six dependent variables about asymmetric wave and sediment characteristics.Asymmetry effects on parameters(orbital amplitude,roughness height,bed shear stress,and boundary layer thickness)are properly considered such that the formula can yield velocity differences among onshore,offshore,acceleration,and deceleration stages.The formula estimates the net boundary layer velocity resulting from the mobile sediment bed and asymmetric boundary layer thickness.In addition,a non-constant phase-lead also contributes to the net boundary layer velocity in asymmetric oscillatory sheet flow.Results of the formula are as good as that of a two-phase numerical model.Sheet flow transport induced by asymmetric waves,and the offshore net sediment transport rate with a large phase-lag under velocity-skewed waves,can be adequately estimated by the formula with a power sediment concentration function.     

Travelling convection vortices in the ionosphere map to the central plasma sheet

We investigate the magnetospheric domain responsible for the generation of ionospheric travelling convection vortices (TCV) by comparing the location of the TCV to the locations of the low-altitude particle-precipitation boundaries deduced from the DMSP satellite measurements. For three very well documented TCV events we are able to identify suitable satellite passes, in the sense that for each event we can identify two to three passes occurring close to the TCV observation in both time and space. In all three cases the comparisons place the TCV centres at or equatorward of the central plasma sheet/boundary plasma sheet precipitation boundary. Thus our results indicate that the field-aligned currents related to the TCV originate in the plasma sheet rather than at the magnetopause or in the low-latitude boundary layer, as previous studies suggest.Permanent address: Polar Geophysical Institute, Apatity, Murmansk region, 184200, Russia     

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.     

Analytical approach for sheet flow transport in purely acceleration-skewed oscillatory flow

An instantaneous analytical approach is developed to predict sheet flow transport in purely acceleration-skewed oscillatory flow. The approach is derived from exponential approximations of velocity and concentration profiles above a mobile seabed, and it particularly considers factors of phase lead; phase lag (i.e. phase residual and phase shift); acceleration modification; and asymmetries in shear stress, roughness height, and boundary layer development. The approach can predict net boundary layer flow above a mobile seabed, and can revert to the classical bedload model. Instantaneous and net sediment transport rates are studied using the approach. The instantaneous sediment transport rate in an onshore flow stage can be approximated by a power function of velocity in which the exponent is confirmed to range between 1 and 5 with a decrease in the phase residual. The net sediment transport rate predicted using the approach is validated using a considerable amount of measured data, and compared with existing instantaneous and half-period type models that consider the phase lag or acceleration modification. For the net sediment transport rate in purely acceleration-skewed oscillatory flow, the phase residual is less important than the acceleration-skewed boundary layer difference between onshore and offshore acceleration stages.     

Quiet-time Pc 5 pulsations in the Earth’s magnetotail: IMP-8, ISEE-1 and ISEE-3 simultaneous observations

Quasi-periodic Pc 5 pulsations have been reported inside and just outside the Earth’s magnetotail during intervals of low geomagnetic activity. In order to further define their characteristics and spatial extent, we present three case studies of simultaneous magnetic field and plasma observations by IMP-8, ISEE-1 (and ISEE-2 in one case) in the Earth’s magnetotail and ISEE-3 far upstream of the bow shock, during intervals in which the spacecraft were widely separated. In the first case study, similar pulsations are observed by IMP-8 at the dawn flank of the plasma sheet and by ISEE-1 near the plasma sheet boundary layer (PSBL) near midnight local time. In the second case study, simultaneous pulsations are observed by IMP-8 in the dusk magnetosheath and by ISEE-1 and 2 in the dawn plasma sheet. In the third case study, simultaneous pulsations are observed in the north plasma sheet boundary layer and the south plasma sheet. We conclude that the pulsations occur simultaneously throughout much of the nightside magnetosphere and the surrounding magnetosheath, i.e. that they have a global character. Some additional findings are the following: (a) the observed pulsations are mixed mode compressional and transverse, where the compressional character is more apparent in the close vicinity of the plane Z_GSM=0; (b) the compressional pulsations of the magnetic field in the dusk magnetosheath show peaks that coincide (almost one-to-one) with similar peaks observed inside the dawn plasma sheet; (c) in the second case study the polarization sense of the magnetic field and the recurrent left-hand plasma vortices observed in the dawn plasma sheet are consistent with antisunward moving waves on the magneto-pause; (d) pulsation amplitudes are weaker in the PSBL(or lobe) as compared with those in the magneto-tail’s flanks, suggesting a decay with distance from the magnetopause; (e) the thickness of the plasma sheet (under extremely quiet conditions) is estimated to be \sim22 R_E at an average location of (X, Y)_GSM=(16, 17) R_E, whereas at midnight local time the thickness is \sim14 R_E. The detected pulsations are probably due to the pressure variations (recorded by ISEE-3) in the solar wind, and/or the Kelvin Helmholtz instability in the low-latitude boundary layer or the magnetopause due to a strongly northward IMF.     

非均匀动压冲击和停止后产生的瞬时重联过程

在非均匀动压冲击期间和冲击突然停止,可引起等离子体边界层的局部瞬时重联过程．本文用二维可压缩ＭＨＤ数值模拟方法研究了这两个过程．结果表明：当大尺度的均匀横向流从一侧边冲击边界层时,磁力线不弯曲,也不发生磁场重联,只是边界层被推着向下游运动;当局部的非均匀动压（特别是横向剪切流）冲击边界层时,被冲击的同向磁场区磁力线逐渐弯曲,在弯曲的反磁场区,出现磁岛,然后在电流片区发生磁场重联,且逐渐形成准稳态的“反Ｋ型”重联结构;当横向剪切流冲击停止后,边界层区变为非常不稳定的系统,产生多种流体涡旋和流型,并相应地产生多种类型的磁场重联结构,直到涡旋消失变为湍动状态时,磁场拓扑才逐渐恢复到未扰动状态。我们提出,外力作用的突然停止,可能是驱动重联的一种新机制,并对这种重联过程在磁层物理中可能的应用进行了讨论．