Three Dimensional Modeling and Computer Simulations of fast magnetic Reconnection

本研究的主题是研究太阳耀斑和地磁亚暴等大耗散事件的基本物理机制。众所周知，涉及慢冲击的快速重联机制非常适用于耀斑现象。那么，一个非常重要的问题是，如何在实际的空间等离子体中发展并建立快速重联机制作为最终解决方案？历史上，关于这个问题提出了两种理论模型。一种是所谓的外部驱动快速重连接模型。在该模型中，外部边界条件决定了基本结构，有限电阻率对快速重联演化没有重要影响。另一方面，我们提出了所谓的自发快速重联模型。在该模型中，由于（微观）局部异常电阻率和（宏观）重联流之间的自洽相互作用，快速重联得以发展。通过大量的计算机模拟，我们已经证明了自发快速重联模型应该最适用于空间等离子体。在自发快速重联模型的基础上，我们得到了（三维）剪切场存在下的基本结果。(1)在慢激波层中，通过大规模的电机效应可以有效地进行相关的磁能转换。(2)大尺度等离子体的形成和传播是自发快速重联机制的直接结果。(3)即使在全三维情况下，如果初始电流片足够大，也可以建立自发快速重联模型。

The main theme of the present research has been directed to studying the basic physical mechanism of large dissipative events, such as solar flares and geomagnetic substorms. It is well understood that the fast reconnection mechanism, involving slow shocks, is quite applicable to flare phenomena. Then, a very essential question is how the fast reconnection mechanism can develop and be established as an eventual solution in actual space plasmas? Historically, two theoretical models have been proposed with respect to this question. One is the so-called externally driven fast reconnection model. In this model, external boundary conditions determine the basic configuration, whereas a finite resistivity plays no important role on the fast reconnection evolution. On the other hand, we have proposed the so-called spontaneous fast reconnection model. In this model, the fast reconnection develops because of the self-consistent interaction between (microscopic) localized anomalous resistivities and (macroscopic) reconnection flows. By a number of computer simulations, we have demonstrated that the spontaneous fast reconnection model should be most applicable to space plasmas. On the basis of the spontaneous fast reconnection model, we have obtained the following fundamental results in the presence of (three-dimensional) sheared fields. (1) The associated magnetic energy conversion can be effectively performed by the large-scale motor effects in the slow-shock layrs. (2) The formation and propagation of a large-scale plasmoid is the direct outcome of the spontaneous fast reconnection mechanism. (3) Even in fully three-dimensional situations, the spontaneous fast reconnection model is available if the initial current sheet is sufficiently large.