模拟IMF北向且By分量占主导时磁层顶重联

本文基于自己开发的全球三维磁层模型, 模拟研究了IMF(Interplanetary Magnetic Field)北向并且B_y分量较大(时钟角为60°)时磁层顶三维结构及其重联图像. 结果发现, IMF B_y为正时, 在北极隙区附近尾-昏侧存在IMF与地磁场之间稳定持续的重联现象;参与重联的地球磁场既有闭合磁力线也有开放磁力线;IMF在北极隙区与地球闭合磁力重联后一端与南磁极相连的磁力线在尾向运动时还可能与北尾瓣的开放磁力线重联而重新闭合, 这种重联与磁力线循环过程不同于同一条IMF磁力线分别在南北半球与地磁场重联的模型. 南极隙区的重联发生在尾-晨侧, 其动力学过程与北极隙区情形类似. 我们的模拟结果表明, IMF B_y较大时不可能发生IMF同一条磁力线分别在南北极隙区重联的情形, 也不会因此而减少尾瓣的开放磁力线.     

2001年1月26日高纬磁层顶通量管事件的观测研究--空间电流密度计算及分析

讨论了三种根据Cluster Ⅱ四颗卫星的磁场测量数据计算空间电流的方法及其误差,论证了这几种方法的内在一致性,并得到了完全相同的计算结果. 进而依据Cluster Ⅱ 磁场探测资料,计算了2001年1月26日多重磁通量管和FTE事件中高纬磁层顶边界层和磁鞘区的电流密度. 结果表明,磁通量管内电流密度较大,可达到约10-8A/m2;计算精度较高,结果可靠. 本文还应用最小方差分析法（MVA）,发现电流方向与通量管的轴向基本一致;论证了电流MVA分析在研究通量管性质时的作用,同时提出了电流管的概念.     

Magnetopause stand-off distance in dependence on the magnetosheath and solar wind parameters

A model of the magnetosheath structure proposed in a recent paper from the authors is extended to estimate the magnetopause stand-off distance from solar wind data. For this purpose, the relationship of the magnetopause location to the magnetosheath and solar wind parameters is studied. It is shown that magnetopause erosion may be explained in terms of the magnetosheath magnetic field penetration into the magnetosphere. The coefficient of penetration (the ratio of the magnetospheric magnetic field depression to the intensity of the magnetosheath magnetic field B_mz = -B_m sin²/2, is estimated and found approximately to equal 1. It is shown that having combined a magnetosheath model presented in an earlier paper and the magnetosheath field penetration model presented in this paper, it is possible to predict the magnetopause stand-off distance from solar wind parameters.     

地球磁层顶K-H不稳定性与撕裂模的耦合及涡旋撕裂模不稳定性

本文用二维MHD数值模拟研究了地球磁层顶同时存在速度剪切和磁场剪切时Kelvin-Helmholtz不稳定性（K-H）和撕裂模不稳定性（TM）的耦合过程。在雷诺数和磁雷诺数确定时,Alfvèn马赫数值（M_A）对耦合特性起决定性作用。在本文选取的参数条件下,若M_A<0.4,自发TM占主导地位;当0.4≤M_A<1.4时,TM受到K-H明显调制;如果M_A≥1.4,K-H引起的涡旋运动起控制作用,导致一种新的不稳定性产生。该不稳定性称作涡旋撕裂模不稳定性。其饱和后长时间渐近状态由一个大尺度的流体涡旋和同心磁岛组成。在地球磁层顶通量传输事件（FTEs）中它可能起着重要作用。     

磁层顶压缩事件的磁场分析

向日面磁层顶在平静太阳风条件下,处于10RE（RE为地球半径）左右．但在异常的太阳风条件下,即南向行星际磁场很强和（或）太阳风的动压很大时,会被压缩,甚至到达同步轨道附近．集中分析2001年4月11日的磁暴事件,研究当磁层顶发生强烈压缩以后。在地球空间和地面上产生的磁场影响．磁层顶位形选取Shue（1998）模型计算．当把计算结果与GOESl0卫星的观测数据对比时发现：磁层顶在强的太阳风条件下的确会被压缩到同步轨道以内．Shue（1998）模型的预测基本正确,通常的漏报可能是由于预报的位置误差所致．实际磁层顶电流片的位置和强度与我们假设的理想磁层顶间断面计算结果基本吻合．在分析大磁暴过程时,磁层顶压缩使磁层顶电流对于中低纬度地磁场扰动有突出的贡献,在2001年4月事件中,这个贡献可以大于50nT,占主相的1／6左右．这一贡献可以使Dst指数产生相应的误差．     

电离层电导对地球磁层顶和舷激波尺度的影响

本文在如下假定下分析电离层电导对地球磁层顶和舷激波尺度的影响：（1）对电离层采用球壳近似,Pedersen电导Σ_P均匀,Hall电导为零;（2）地磁偶极矩处于正南方向,行星际磁场（IMF）只有南向分量（B_z<0）.磁层顶和舷激波的尺度分别由它们与GSE坐标系三个轴的交点,即日下点、晨昏侧翼点和南北顶点的地心距离表征.对给定的太阳风条件、B_z和Σ_P,通过三维全球MHD模拟获得系统的准定态.结果表明,在大约1～5 S范围内,Σ_P值显著影响磁层顶和舷激波的尺度,而在该范围之外则几乎没有影响.随着Σ_P的增加,磁层顶和舷激波整体向外扩张,前者的扩张程度低于后者,以至磁鞘区的范围扩大.磁层顶的侧翼点的位置随Σ_P的变化与B_z的幅度有关：在弱南向IMF情况下磁层顶的侧翼点随Σ_P的增加向内移动,而在强南向IMF情况下则向外移动.上述结果表明,在构建磁层顶和舷激波的经验模型时,有必要计入电离层电导的影响.     

The Kelvin-Helmholtz instability at Mercury: An assessment

The Kelvin-Helmholtz instability is believed to be an important means for the transfer of energy, plasma, and momentum from the solar wind into planetary magnetospheres, with in situ measurements reported from Earth, Saturn, and Venus. During the first MESSENGER flyby of Mercury, three periodic rotations were observed in the magnetic field data possibly related to a Kelvin-Helmholtz wave on the dusk side magnetopause. We present an analysis of the event, along with comparisons to previous Kelvin-Helmholtz observations and an investigation of what influence finite ion gyro radius effects, believed to be of importance in the Hermean magnetosphere, may have on the instability. The wave signature does not correspond to that of typical Kelvin-Helmholtz events, and the magnetopause direction does not show any signs of major deviation from the unperturbed case. There is thus no indication of any high amplitude surface waves. On the other hand, the wave period corresponds to that expected for a Kelvin-Helmholtz wave, and as the dusk side is shown to be more stable than the dawn side, we judge the observed waves not to be fully developed Kelvin-Helmholtz waves, but they may be an initial perturbation that could cause Kelvin-Helmholtz waves further down the tail.     

同步轨道磁场和地面磁场对太阳风动压变化事件的响应

本文对磁宁静时的123个动压变化事件(不包含激波事件)进行了统计研究.研究表明,在白天侧(9～15MLT)同步轨道磁场z分量对太阳风动压增大、减小事件具有较强的正响应,而在夜侧(21～3MLT)响应明显减弱,响应幅度具有明显的磁地方时分布.对动压增大事件的平均响应幅度在午前最大,而对动压减小事件的平均响应幅度在午后达到...     

Relationship between the ionospheric conductance, field aligned current, and magnetopause geometry: Global MHD simulations

The role of the ionospheric conductance in the solar wind-magnetosphere coupling is studied using global MHD simulations. The simulations with varying conductance and a constant solar wind input show that the field-aligned currents, whose magnitude depends on the ionospheric conductance, affect the size of the magnetopause at the flanks by increasing the local magnetic pressure and thus altering the surface equilibrium at the magnetopause. A current system that generates the magnetic stresses required to account for the location and geometrical structure of the magnetosphere observed in the simulations is proposed.     

Interaction of interplanetary shocks with the bow shock

Fast forward interplanetary (IP) shocks have been identified as a source of large geomagnetic disturbances. However, the shocks can evolve in the solar wind, they are modified by interaction with the bow shock and during their propagation through the magnetosheath. A few previous papers refer the inclination and deceleration of the IP shock front in this region. Our contribution continues this effort and presents the study of an IP shock interaction with the bow shock. Since the bow shock is a reversed fast shock, the interaction of the IP shock and bow shock is a problem of interaction of two fast MHD shocks.

We compare profiles of magnetic field and plasma parameters observed by several spacecraft in the solar wind and magnetosheath with the profiles of the same parameters resulting from the MHD numerical model. The MHD model suggests that the interaction of an IP shock with the bow shock results in an inward bow shock displacement that is followed by its outward motion. Such motion will result in an indentation propagating along the bow shock surface. This scenario is confirmed by multipoint observations. Moreover, the model confirms also previous suggestions on the IP shock deceleration in the magnetosheath.