Numerical study on physics on physics of auroral pattern formation and plasma elementary processes

(1)对极光投射到电离层特征模式的理论研究阐明了磁层/电离层系统自然现象的基本等离子体物理学。首先，磁层中电荷分离的过程已被确定为极光行进浪涌、欧米茄带和涟漪的原因。（这些极光现象的原因长期以来一直超出理论研究人员的理解范围。）我们的方法是独特的：通过使用粒子模拟，我们重现了电离层上极光的时空发展，这与观测结果很好地吻合。我们进一步将基于仿真的分析应用于准稳态场向电流问题。与极光动力学的情况类似，我们通过二维模拟成功地再现了观测发现的1区和2区场向电流的模式。这一结果自然导致了一个新的概念，即在极帽区外部施加太阳风时，封闭磁层中的等离子体扭曲可以产生配对的1区/ 2区场向电流。(2)利用Tsyganenko的d磁场模型，数值计算了行星际磁场影响相对较小的磁封闭区域的磁漂移矢量分布。从图中我们发现低纬度边界层（LLBL）的场向流可能是由磁鞘注入的等离子体的压力梯度引起的。（该论文将于1995年3月在经济和社会发展战略会议上提出。）我们还将论证，最近卫星观测揭示的LLBL电流系统的一些特征，不能用磁层和太阳风之间粘性相互作用的模型来理解，而粘性相互作用一直被认为是LLBL电流产生的最可能的机制。

(1) Our theoretical study on the characteristic pattern of auroras projected on the ionosphere has elucidated fundamental plasma physics for natural phenomena in the magnetosphere/ionosphere system. First, the processes of charge separation in the magnetosphere have been identified as being responsible for the auroral traveling surge, the omega bands, and the ripples. (The causes of these auroral phenomena had long been beyond understanding of theoretical researchers.) Our approach is unique : by using particle simulations we reproduce the temporal/spatial development of auroras on the ionosphere which is in good agreement with the observations. We further apply the simulation-based analysis to the problem of quasi-steady field-aligned currents. Similarly to the case of auroral dynamics, we successfully reproduced the observatioanlly identified pattern of region 1 and region 2 field-aligned current by the two dimensional simulations. This result leads naturally to a new concept that the paired region 1/region2 field-aligned currents can be produced from the plasma distortion in the closed magnetosphere by the solar wind externally applied in the polar cap region.(2) Using the d magnetic field model by Tsyganenko, we numerically obtained the distributions of magnetic drift vectors in the magnetically closed region where the effect of the interplanetary magnetic field is relatively small. From this plot we found that the field-aligned currents in the low-latitude boundary layr (LLBL) is likely to be caused by the pressure gradient of a plasma injected from the magnetosheath. (Paper will be presented at SGEPSS,in March 1995.) We will also argue that some features of the LLBL current system, which have been revealed by recent satellite observations, could not be understood in a model of the viscous interaction between the magnetosphere and the solar wind which had long been believed to be a most likely mechanism for the LLBL current generation.