上行离子流对亚暴膨胀相起始的触发作用

【作者】 张灵倩；

【导师】 刘振兴；

【作者基本信息】 中国科学院研究生院（空间科学与应用研究中心） ， 空间物理学磁层物理， 2005， 博士

【摘要】 磁层亚暴则是地球空间最重要的能量输入、耦合和耗散过程。磁层动力学最为重要的研究任务就是对磁层亚暴的理解。亚暴膨胀相是亚暴最为活跃的部分。膨胀相的触发机制现在还不明确。这是空间物理领域最为核心和前沿的问题之一。上行离子作为磁层-电离层耦合的重要方式,不仅对磁层的粒子成分有着重要的影响,同时上行离子对磁尾动力学过程有重要的影响。我们知道电离层是磁层H⁺和O⁺的重要源区,高纬电离层为磁层提供高通量的低能（热）等离子体,总的质量可以达到1kg/ s^-1。这样高通量的上行离子对磁层的离子成分和动力学的影响迄今仍是一个疑问。上行离子流（ions upflow）同时对亚暴过程也有着重要的影响,它有可能是膨胀相起始（substorm onset）的触发机制。对这个问题的研究无疑是具有重要意义的。我们利用三维MHD 方法首次对上行离子流触发的亚暴膨胀相起始过程进行了研究。主要的模拟工作包括下面几个部分: （1）磁静时起源于夜侧电离层极光椭圆带源区的上行离子对磁尾等离子体片动力学过程的影响; （2）在同样的磁场位型下,对流电场对磁尾等离子体片动力学过程,主要是亚暴增长相（growth phase）和膨胀相起始的影响; （3）在亚暴增长相期间,上行离子流对膨胀相起始的触发作用等问题进行了模拟研究。由于亚暴膨胀相起始的重要标志是场向电流（field-aligned current）的突然增加,我们对每个过程中场向电流的特性都进行了重点分析。第一部分的研究主要是为了了解起源于夜侧电离层极光椭圆带源区的上行离子对场向电流的影响及可能引起近地磁尾电流片不稳定性的机制。在第三章我们详细介绍了这部分工作。这部分工作的主要结果包括: ·上行离子对磁尾的影响主要发生在近地区域。上行离子对磁尾的影响与上行离子的通量密切相关,上行离子的通量越高,影响越大。·随着进入磁尾的上行离子通量的增加,磁尾尤其是在近地等离子体片内更多还原

【Abstract】 It is well known that the ionosphere is an important source of magnetospheric plasma, especially H⁺ ions and O⁺ ions, the high latitude ionosphere transport the high flux and low energy （hot） plasma to the magnetosphere, the whole quality is up to 1kg/ s^-1. The effect of such high flux upflowing ions on the composition and the dynamic process of the magnetosphere is still unclear. The key problem is if the ions upflow can really trigger the substorm onset? A 3-D resistive MHD simulation is carried out to study the effect of the ions upflow on the dynamic process of the magnetotial and the triggering of the substorm onset. The whole work is divided into three parts: （1） The effects of the ions upflow original from the night-side auroral oval on the near-earth magnetotail during the quiet time; （2） The effect of the convection electric field on the dynamic process of the magnetotail, mainly on the substorm growth phase and the onset process; （3） The effect of the ions upflow presented during the substorm growth phase on the substorm process, the most interesting question is if the ions upflow can trigger the substorm onset. In the magnetotail, one of the most significant observational features at substorm onset is the sudden enhancement of the field-aligned current and an increase of the north-south component of the magnetic field （Bz） up to its dipolar value, so we especially analysis the change of the field-aligned current and the Bz in each part. The first part of the simulation is to understand the effects of the ions upflow original from the night-side auroral oval on the near-earth magnetotail during the quiet time. This is important for us to understand the current instability triggered by the upflows in the near earth region. The main conclusions include that: ·During the quiet time, the up-flowing ions original from the night-side auroral oval have effect mainly on the near-earth magnetotail. The effect of the upflow ions on the dynamic process of the magnetotail depends on the flux of the upions entered the plasma sheet. The main effects include: （1） with the entering of the upflowing ions, the pressure in the near-earth plasma sheet decrease; （2） the density of the plasma in the plasma sheet decrease; （3） the cross-tail current increase in the near-earth region, and decrease beyond 20Re in the plasma sheet; （4） the plasma flow in the plasma sheet is the earth-direction inside 20Re, and the tail-direction outside 20Re. This is important for us to understand the role of the upflowing ions on the substorm process. Inducing the enhancement of field-aligned current in the near-earth magnetotail. The distribution region of the FAC is mainly divieed into three regions, including: high-latitude region, mid-latitude region and plasma sheet boundary. The distribution of the FAC in the dark-aside and dawn-aside have reversal multi-layer structure, including low-latitude. The intensity of the FAC depends not only on the up-flowing ions energy flux transfer into the plasma sheet, but also on the velocity of the upflows. The second part of the simulation is to understand the substorm process under the effect of the convection electric field, and forming the thin current sheet in the magnetotail. The main conclusions include that: The convection electric field have important effects on the location of the X-line and the process of the substorm With the growth of the magnetic-island in the x and z direction, the plasmoid moved tail-ward, and the near-earth X line moved earth-ward fastly. The moving velocity of the X-line mainly depends on the convection electric field. With the earth-ward moving of the X-line, the significant symbol of the substorm is presented, including the thinning of the plasma sheet, the increasement of the cross-tail current and the forming of the thin current sheet in the near-earth magnetotail The third part is based on the results of the second part, and is mainly about the triggering of the current instability by the ions upflow original from the night-side auroral oval. This can induce the substorm onset during the late growth phase. The main conclusions include that:更多还原