Three Dimensional Modeling and Computer Simulations of fast magnetic Reconnection

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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.