等离子体彗尾动力学的数值研究

本文基于可压缩磁流体动力学模型,数值研究了尾瓣巾具有超Alfven速流动的等离子体彗尾的动力学特征。结果表明,等离子体片和尾瓣之间的剪切等离子体流动将会激发流动撕裂模不稳定性,引起彗尾等离子体片中发生磁场重联,形成磁岛和高密度的等离子体团。进而模拟了太阳风引起的局部驱动力对等离子体彗尾中磁场重联的影响,其特征时间远大于流动撕裂模。我们认为一些观测到的等离子体彗尾中的四块和彗尾截断事件可能主要与彗尾中剪切等离子体流动所引起的流动撕裂模不稳定性有关。      

彗尾剪切磁流体的修正B—KdV方程及其非线性特征

本文运用二维约化摄动方程推导出彗尾剪彻磁流体的修正B-KdV方程,并定性讨论了其非线性性态。主要结论是:(1)推导出彗尾剪切磁流体修正的B-KdV方程,(2)给出彗尾宏观非线性波动与剪切背景的制约关系,(3)定性地解释了彗尾等离子体的一些复杂结构,(4)给出太阳风与彗尾等离子体相互作用的一种输运机制。     

太阳风与彗尾等离子体相互作用引起不稳定的一种讨论

本文讨论了在无力场情形下,太阳风与彗尾等离子体相互作用的二流不稳定问题。应用International Cometary Explorer(ICE)飞行器对彗星Giacobini-Zinner的探测数据,采用合理的等离子分布形式,得出的结论是在彗星内部存在着这种二流不稳定现象。      

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。     

Ⅰ型彗尾中MHD波的特征分析

本文根据Ⅰ型彗尾的背景材料，分析了MHD波的色散关系，探讨了螺旋波的稳定性及其演变的特征．根据初始条件的不同，有的彗尾中可以产生稳定的螺旋波，有的则不然，只能是浑云状态．文章给出了理论推演，列出了观测结果，理论和观测能较好地符合．可进一步结合Hale－Bopp彗星的观测，进行对比和检验．     

日地空间电磁环境和彗星之间的相互作用的分析和讨论

本文根据对彗星资料进行的统计分析, 指出彗尾的出现是随机的;并对各种观测到的彗星现象, 例如I型彗尾骚动、I型彗尾扭折、以及彗尾边界和磁层顶相遇等现象, 与空间电磁环境的关系进行了分析研究, 认为不同的现象有比较相似的统计结果, 但有不相同的相互作用的机理.      

史汪彗星的彗尾

史汪彗星彗尾里的纹纹路是怎么产生的?2006年11月,史汪彗星意外增亮到肉眼可见的程度,而离子尾也出现了幽灵般变幻的细部构造.离子尾是由太阳紫外线游离的体所构成,并在太阳风的推送下离开太阳.太阳风本身就具有很强的结构性,并深受太阳变幻莫测的磁场的挟制.     

I型彗尾风差角的分析及其所显示的太阳风的传播特性

文章分析了I型彗尾风差角的大量资料, 得出其变化和日心距离的关系是不大的;但对日心黄纬, 却显示出逐渐减小的趋向.文章还得出, 风差角的变化随着彗星的切向速度而单调上升, 从而进一步证实了动力风差原理是形成风差角的主要因素.在此基础上, 分析了太阳风速度场的分布特性, 得出了平均太阳风速度随日心距离的变化是不明显的, 而随日心黄纬有着缓慢增强的趋势.      

哈雷彗星等离子体彗尾亮度分布的理论分析

本文借助Nazarchuk的扩散理论模型和有关资料, 分析了1986年1月4日哈雷彗星等离子体彗尾的尾轴方向及其垂直方向的相对亮度分布, 推算出CO+离子的平均寿命、纵向(沿尾轴)和横向扩散系数, 估算了磁场强度, 最后进行一些讨论.      

从鹿林彗星认识彗尾

2010年上半年，最耀眼的彗星莫过于鹿林彗星，因为它来自太阳系外围的奥尔特星云，若轨道呈双曲线，这会是它唯一一次造访太阳系内部。而且相较于其他来自奥尔特星云的彗星，它算是非常接近地球的一个，近地点约只有0.41天文单位（相当于6100万千米），使得不少天文专家日以继夜守着它，才能捕捉到难得一见的彗尾断裂、长时间“反向”彗尾等景象。     

How cosmic rays were discovered and why they received this misnomer

As many great discoveries, the phenomenon of cosmic rays was discovered mainly accidentally, during investigations that sought to answer another question: what are sources of air ionization? This problem became interesting for science about 230 years ago in the end of the 18th century, when physics met with a problem of leakage of electrical charge from very good isolated bodies. We describe the history how step by step cosmic rays was discovered and why this phenomenon received misnomer, how in cosmic rays was discovered the first antiparticle – positron. These discoveries were recognized among greatest in the 20th Century and were awarded by Nobel Prize.     

Dynamics of the plasma sheet in the magnetotail: Interrelation of turbulent flows and thin current sheet structures

Dynamics of the magnetotail involves elementary processes of magnetic field merging (reconnection layer formation) occurring on medium spatial scales. Every such process features two different stages, a fast one and a subsequent slower one. The corresponding short time scale _T1$T_1$ is associated with disturbances propagating in the tail lobes. The longer time scale _T2$T_2$ is associated with plasma motions in the plasma sheet. A disturbance appearing in the magnetotail on the time scale _T1$T_1$ results in a loss of equilibrium in the plasma sheet. By means of theoretical argument and numerical simulation, it is shown that the relaxation process which follows on the time scale _T2$T_2$, produces extremely thin embedded current sheets, along with generation of fast plasma flows. The process provides an effective mechanism for transformation of magnetic energy accumulated in the magnetotail, into energy of plasma flows. The fast flows may drive turbulent motions on shorter spatial scales. In their turn, those motions can locally produce very thin current sheets; after that, nonlinear tearing process leads to generation of neutral lines, and reconnection. The latter produces new fast disturbances on the time scale _T1$T_1$ closing the feedback loop.     

Fluctuations of cosmic rays and IMF in the vicinity of interplanetary shocks

Fluctuations of cosmic rays and interplanetary magnetic field upstream of interplanetary shocks are studied using data of ground-based polar neutron monitors as well as measurements of energetic particles and solar wind plasma parameters aboard the ACE spacecraft. It is shown that coherent cosmic ray fluctuations in the energy range from 10 keV to 1 GeV are often observed at the Earth’s orbit before the arrival of interplanetary shocks. This corresponds to an increase of solar wind turbulence level by more than the order of magnitude upstream of the shock. We suggest a scenario where the cosmic ray fluctuation spectrum is modulated by fast magnetosonic waves generated by flux of low-energy cosmic rays which are reflected and/or accelerated by an interplanetary shock.     

On possible genesis of fractal dimensions in the turbulent pulsations of cosmic plasma – galactic cosmic rays – turbulent pulsation in planetary atmosphere system

The spectrum of turbulent pulsations induced in the atmosphere by the galactic cosmic rays is defined. A possible manifestation of genesis of fractal dimensions in the system of “spectrum of turbulent pulsations of cosmic plasma – galactic cosmic rays’ spectrum – spectrum of atmospheric turbulent pulsations” is analyzed.     

Injection mechanism for cosmic ray acceleration

The quasilinear theory of MHD waves excitation by cosmic rays accelerated at a front of supernova shock has been constructed. It is shown that the energetic particles excite the waves propagating from the shock front, the intensity and the spectrum of these waves is obtained. The role of nonlinear Landau damping in the formation of such spectrum has been analysed. The diffusive scattering length of the high energy particles in the preshock region has been calculated and it is shown with the help of these formulae that the effective Fermi acceleration at the shock front is possible upto the values of the relativistic factor = 10⁴ - 10⁵. The injection mechanism for cosmic rays acceleration has been proposed. It is based on stochastic Fermi acceleration of the thermal plasma by MHD waves excited in the preshock region. Different possibilities for wave phase velocity dispersion needed for stochastic Fermi acceleration are analysed, those are the excitation of the oblique magnetosonic waves as well as the excitation of parallel Alfven waves propagating in opposite directions. The distribution function of the suprathermal particles accelerated by MHD waves is obtained, the cosmic rays density as well as the lower boundary of their energy spectrum realised in the proposed mechanism are also calculated.     

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.     

Study of the radiation environment on MIR space station with SILEYE-2 experiment.

In this work we present preliminary results of nuclear composition measurements on board space station MIR obtained with SILEYE-2 particle telescope. SILEYE-2 was placed on MIR in 1997 and has been working since then. It consists of an array of 6 active silicon strip detectors which allow nuclear and energetic identification of cosmic rays in the energy range between approximately 30 and 200 MeV/n. The device is attached to an helmet and connected to an eye mask which shields the cosmonaut eyes from light and allow studies of the Light Flashes (LF) phenomenon. In addition to the study of the causes of LF, the device is used to perform real time long term radiation environment monitoring inside the MIR, performing measurements in solar quiet and active days.     

低仰角射线对电离层CT成像的影响分析

电离层层析成像(Computerized Tomography, CT)是一个有限视角问题, 水平射线的缺失造成CT结果垂直分辨率的严重下降. 很多人直观地认为低仰角射线可以弥补水平射线的缺失, 然而本文的理论分析和数值模拟研究结果表明, 低仰角射线对CT结果的影响十分微小, 其无法弥补水平射线缺失所带来的垂直分辨率的下降. 模拟结果显示, 增加低仰角射线前后CT反演结果几乎没有变化; 而去掉680条低仰角射线和高仰角射线后, CT反演结果差别巨大; 去掉680条低仰角射线的CT结果与模型吻合很好; 去掉680条高仰角射线的CT反演结果失真严重, 几乎无法恢复模型的扰动特征.      

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.