Kinetic theory of the current sheath. II. Effect of polarization on the stability of a current sheath

A procedure for investigating the stability of a current sheath, taking into account the effect of plasma polarization, is offered. The kinetic equation with a self-consistent electromagnetic field for perturbation of the distribution function is solved. On the basis of this solution, the tensor of dielectric permeability for a non-electroneutral current sheath plasma is calculated, and the dispersion equation for the study of possible instability modes of this current sheath is obtained. The instability of the current sheath of the magnetospheric tail with respect to tearing perturbations, and the influence of the effect of plasma polarization on the development of tearing instability, are investigated.     

Topology of the high latitude magnetosphere during large magnetic storms and the main mechanisms of relativistic electron acceleration

One of the main endeavors of the “Space Weather” program is the prediction of the appearance of very large fluxes of relativistic electrons with energies larger than 1 MeV, because they represent a serious potential hazard for satellite missions. Large fluxes of relativistic electrons are formed in the outer radiation belt during the recovery phase of some storms. The formation of large fluxes is connected to a balance between the acceleration and loss processes. A two-step acceleration process is ordinarily analyzed. A “Seed” population with energies ∼hundreds of keV appeared during expansion phase of magnetospheric substorm. A “Seed” population is additionally accelerated obtaining relativistic energies by some other process. Several acceleration mechanisms have been proposed for the explanation of the electron acceleration, including radial diffusion and internal acceleration by wave-particle interactions. Nevertheless, none of them takes into account great changes of magnetospheric topology during a magnetic storm. Such changes are mainly connected with asymmetric and symmetric ring current development. We analyze the changes of magnetospheric topology during magnetic storms. We show that a change of the magnetospheric magnetic field can be the important factor determining the acceleration of relativistic electrons.     

Case study of September 24–26, 1998 magnetic storm

We compute global magnetospheric parameters based upon solar wind data obtained from the WIND spacecraft upstream. Using the paraboloid magnetospheric model, calculations of the dynamic global magnetospheric current systems have been made. The solar wind dynamic pressure, the interplanetary magnetic field, the strength of the tail current, and the ring current control the polar cap and auroral oval size and location during the magnetic storm. The model calculations demonstrate that the polar cap and the auroral oval areas are mainly controlled by the tail current. The substorm onset at 0630 UT on September 25, 1998 happened near the minimum in the main phase field depression. The substorm expansion onset time is also marked by a sudden enhancement in the solar wind dynamic pressure and an enhancement in the tail current. The magnetic signatures of these two effects cancel each other, which explains why the D_st profile shows no strong time variation during the substorm. Evidence for the substorm expansion includes not only the signature in the AL index but also the strong asymmetry of the low latitude magnetic disturbances (substorm positive bay signature). Model calculations were checked by comparison with the GOES 8 and 10 magnetic field measurements.     

Simultaneous investigation of magnetospheric plasma and spacecraft charging

The results of magnetospheric plasma fluxes measurement in geosynchronous orbit are presented. The measurements were done onboard the geosynchronous Russian “Electro” spacecraft (SC) in 1995–1997 years. The diurnal variations of the plasma density and temperature were observed at various levels of geomagnetic activity.     

磁静日期间中国大陆地区外源弱磁场研究

利用第四代地磁场综合模型CM4, 研究了中国大陆地区1960-2000年磁静日期间地磁外源弱磁场的变化情况, 计算并分析了外源场中的电离层感应场、环形场以及磁层感应场的分布和变化. 结果显示, 北向分量X的磁层感应场强度总体呈先增加后减少的趋势, 共减少了约7.3nT; 东向分量Y的磁层感应场强度呈先减少后增加的趋势, 共增加了约0.8nT; 垂直分量Z的磁层感应场强度呈先增加后减少的趋势, 共增加了约5.5nT. 三个分量的电离层感应场以及环形场变化幅度很小, 其分布在1960-1970和1970-1980年, 1980-1990 和1990-2000年呈现正负互相变换的现象, 认为该现象可能与太阳11年活动周期有关. 最后对弱磁场随时间变化的结果进行了分析说明.      

使用GAO-YONG湍流方程组对扩压器流动的计算

采用基于同位网格的SIMPLE方法求解GAO-YONG不可压湍流方程组,对二维扩压器流动进行了数值模拟.通过界面速度动量插值法解决了压力锯齿波问题,并且采用了正交贴体网格和二阶QUICK格式离散对流项以提高计算精度.与实验结果以及BL(Baldw-Lomax)模型计算结果的比较表明,不需要任何经验系数及壁面函数的GAO-YONG不可压湍流模型方程组能够对有压力梯度的湍流流动做出很好的预测.计算发现,在机械能方程中引入平均流压力梯度的作用,对GAO-YONG湍流方程组正确模拟逆压力梯度流动起到了关键作用.      

MAGNETOSPHERIC PHYSICS IN CHINA:2000-2002

This brief report presents the latest advances of the magnetospheric physics researches in China during the period of 2000-2002, made independently by Chinese space physicists and through international cooperation. The related areas cover almost every aspect of magnetospheric physics.     

Progress of Double Star Program 2006-2008

This paper presents the status of two satellites of Double Star Program, and a part of scientific results based on the data of Double Star Program obtained during the period of 2006-2008.Other scientific results in the magnetospheric physics research can be found in "Multi scale physical process in the magnetosphere" of this issue.      

PC-index fluctuations and intermittency of the magnetospheric dynamics

One minute resolution Polar Cap (PC) index was used for the analysis of magnetospheric dynamics. The 1995–2000 time series analysis revealed that the power spectrum of the PC-index fluctuations is a power law in a wide range of frequencies. However, the obtained exponents differ for low and high frequency regions. The probability distribution functions of the PC-index fluctuations show a strong non-gaussian shape, depending on the time of increment. This indicates that the PC-index exhibits intermittency, previously detected in solar wind and auroral electrojet index fluctuations. The PC-index probability distribution functions were fitted by the functional form proposed by Castaing et al. [Velocity probability density functions of high Reynolds number turbulence. Physica D. 46, 177–200, 1990] to describe intermittency phenomena in ordinary turbulent fluid flows. The agreement between the fitting parameters obtained for the PC index and those reported before for solar wind magnetic field fluctuations is within 30%; which is noticeably less than the difference between the same parameters of solar wind and the AE-index fluctuations. This fact indicates that the PC index reflects the solar wind influence on the high-latitude magnetosphere, especially during the summer.     

Magnetospheric Physics in China:2002-2004

This brief report presents the latest advances of the magnetospheric physics researches in China during the period of 2002-2004. The progress of the magnetospheric space mission DSP is given in another dedicated paper of this issue.     

Scientific progress of combined exploration DSP and Cluster: 2008—2010

The combined observations of Double Star and Cluster missions allow for, for the first time, six-point measurements of the main plasma parameters in the key scientific regions of the near-Earth environment. In the past two years, a great number of works were made based on the data from DSP and Cluster missions, advancing remarkably the research of magnetospheric physics in China. This paper briefly reviews these important scientific results based on 51 selected publications.      

晨昏电场对磁亚暴触发的影响

本文讨论了晨昏电场存在时磁尾等离子体片内撕裂模不稳定性的激发和增长问题。得到的结果可以用来解释晨昏电场对磁亚暴的触发以及加快等离子体片贮存能量的耗散等现象。我们推导了存在电场漂移时的撕裂模方程,并在均匀电流片模型下求解了该方程的解析解。结果表明触发不稳定性所允许的临界电流片宽度与电场大小近似成正比,这表明考虑晨昏电场效应后磁亚暴更易被激发。此外对于厚度相同的电流片来说,长波撕裂模的增长率也随晨昏电场的加强而增大。      

Magnetospheric Physics in China: 2012–2014

In the past two years, many progresses have been made in magnetospheric physics by using the data of Double Star Program, Cluster, THEMIS and RBSP missions, or by computer simulations. This paper briefly reviews these works based on papers selected from the 126 publications from March 2012 to March 2014. The subjects cover various sub-branches of magnetospheric physics,including geomagnetic storm, magnetospheric substorm and magnetic reconnection.     

MHD surface waves – a source of global magnetospheric modes (resonances)?

Various mechanisms have been proposed for explanation of the global magnetospheric modes whose frequency peaks are in the frequency range 1–4 mHz. Recent papers claim: basic characteristics of the 1–4 mHz activity events observed on ground give evidences for an existence of MHD surface mode excited on the Earth magnetopause. The discrete frequencies of such MHD surface wave modes suggest an emergence of standing wave structures along the magnetic field lines lying on the magnetopause. Such discrete frequencies of MHD surface waves on magnetopause however, are not stable, at all. Contrariwise, MHD surface wave modes supported by the two plasma boundaries – the magnetopause and the plasmapause, are in accordance with existing experimental facts: discrete set of almost stable frequencies, field amplitude peaks and positions, energy dissipation, and field distribution from high to low latitudes. Mechanisms of the global magnetospheric mode resonance are pointed out as well as tools for their identification and discrimination.     

Current sheet with medium scale developed turbulence and the formation of the plasma sheet of Earth''s magnetosphere and solar prominences

A current sheet model with developed medium scale turbulence has been constructed. It is suggested that regular plasma flow in the current sheet is compensated by diffusive flux and plasma mixing, leading to temperature equalization. The analyzed turbulence has the form of electrostatic vortices in which electrons and ions move with the same velocities and hence does not lead to anomalous resistivity and current dissipation. It is possible to determine the plasma pressure dependence on magnetic vector potential and to find the Grad—Shafranov equation solutions. The theory is used to explain the Earth's magnetosphere plasma sheet characteristics. It is taken into account that experimentally observed plasma velocity fluctuations in the Earth's plasma sheet and quiescent prominences are much higher than regular plasma flow velocities. The analysis of turbulent current sheet dynamics after the regular motion weakening allows to construct the prominence formation theory. The decreasing of plasma pressure in the sheet due to diffusion leads to field-aligned plasma flow and plasma tube filling by cold chromospheric plasma by the action of siphon mechanism.     

用GAO-YONG湍流模式对翼型跨音粘流的数值模拟

应用GAO-YONG可压缩湍流模式,数值模拟了NACA0012,RAE2822翼型的定常跨音速粘流算例.对流项采用三阶ROE格式,扩散项采用二阶中心格式,用多步Runge-Kutta显式时间推进法求解空间离散后的控制方程.计算结果很好地预测了翼型表面的压力系数的分布、激波的位置、马赫数等值线的分布等情况,并且对翼型表面激波与边界层相互干扰以及层流向湍流的转捩问题进行了分析计算.计算结果与实验值符合很好,表明GAO-YONG可压缩湍流模式应用合适的计算方法能够高精度模拟翼型跨音粘性流动问题,并且基于GAO-YONG可压缩湍流模式各向异性湍流粘性的机理,提供了一种预测转捩起始位置的判别方法.      

In situ measurements of ionospheric plasma turbulence over five frequency decades: Heritage flight of the Plasma Local Anomalous Noise Experiment (PLANE)

Observations of ionospheric plasma density and frequency-dependent broadband plasma turbulence made during the heritage flight of the Plasma Local Anomalous Noise Experiment (PLANE) are presented. Rather than record high frequency time series data, the experiment was designed to record Power Spectral Distributions (PSDs) in five decadal frequency bins with upper limits ranging from 1.0 Hz to 10 kHz. Additionally, PLANE was designed distinguish turbulence in the ambient plasma from that local to the spacecraft. The instrument consists of two retarding potential analyzers (RPAs) connected together via a feedback loop to force one analyzer into the I–V trace retardation region at all times. Fluctuations in this measurement are believed to be ambient only as the RPA’s voltage would be too high for locally turbulent plasma to surmount the potential barrier, which is nominally at ram energy. The instrument requires pointing along the spacecraft’s ram velocity vector to make this measurement, thus requiring stabilization in pitch and yaw. During PLANE’s heritage flight, though the satellite’s attitude control system failed early in the mission, plasma data were collected during opportune times in which the instrument rotated into and out of the ram. Observations of plasma density and PSDs of high frequency plasma turbulence were recorded on several occasions. Additionally, a plasma source onboard the satellite was used to generate artificial plasma turbulence, and the PLANE data observed periodic structure presumably associated with the rotation of the spacecraft during these source firings. A brief comparison with other high frequency in situ plasma instruments is presented.     

Magnetospheric disturbances associated with the 13 December 2006 solar flare and their ionospheric effects over North-East Asia

We present an observational study of magnetospheric and ionospheric disturbances during the December 2006 intense magnetic storm associated with the 4В/Х3.4 class solar flare. To perform the study we utilize the ground data from North–East Asian ionospheric and magnetic observatories (60–72°N, 88–152°E) and in situ measurements from LANL, GOES, Geotail and ACE satellites. The comparative analysis of ionospheric, magnetospheric and heliospheric disturbances shows that the interaction of the magnetosphere with heavily compressed solar wind and interplanetary magnetic field caused the initial phase of the magnetic storm. It was accompanied by the intense sporadic E and F2 layers and the total black-out in the nocturnal subauroral ionosphere. During the storm main phase, LANL-97A, LANL 1994_084, LANL 1989-046 and GOES_11 satellites registered a compression of the dayside magnetosphere up to their orbits. In the morning–noon sector the compression was accompanied by an absence of reflections from ionosphere over subauroral ionospheric station Zhigansk (66.8°N, 123.3°E), and a drastic decrease in the F2 layer critical frequency (foF2) up to 54% of the quite one over subauroral Yakutsk station (62°N, 129.7°E). At the end of the main phase, these stations registered a sharp foF2 increase in the afternoon sector. At Yakutsk the peak foF2 was 1.9 time higher than the undisturbed one. The mentioned ionospheric disturbances occurred simultaneously with changes in the temperature, density and temperature anisotropy of particles at geosynchronous orbit, registered by the LANL-97A satellite nearby the meridian of ionospheric and magnetic measurements. The whole complex of disturbances may be caused by radial displacement of the main magnetospheric domains (magnetopause, cusp/cleft, plasma sheet) with respect to the observation points, caused by changes in the solar wind dynamic pressure, the field of magnetospheric convection, and rotation of the Earth.     

彗星穿越过境对磁层的影响及其分析讨论

对哈雷、百武和海尔-波普三颗慧星在不同时间、不同位置的情况下5次过近地点可能引起对地球磁层影响进行了资料分析和统计研究，指出，根据等离子体彗尾的特征，完全可以对磁层引起扰动，但是这种扰动有严格的制约条件，不是每次彗星过境都很容易对地球电磁环境产生影响。