Computer studies on the spontaneous fast reconnection evolution in various physical situations

The spontaneous fast reconnection evolution is studied in a long current sheet system in various physical situations, where the threshold of current-driven anomalous resistivity is assumed to increase with the thermal velocity. If the initial threshold VC0 is sufficiently large in a low-β plasma, the fast reconnection mechanism can fully be set up; on the other hand, if VC0 is so small that the anomalous resistivity can easily occur in the usual circumstances, the resulting diffusion region notably lengthens so that the reconnection process becomes much less effective. Also, the fast reconnection evolution is strongly influenced by plasma β in the ambient magnetic field region, and an essential condition for the fast reconnection mechanism to evolve explosively is that the plasma β is sufficiently small. In fact, only in a low-β plasma does the magnetic tension force involved play the dominant role in the overall system dynamics and in the drastic magnetic energy release. It is also demonstrated that the fast reconnection evolution does not depend on the detailed functional form of the (current-driven) anomalous resistivity model. This is because the positive feedback between the anomalous resistivity and the reconnection flow effectively works so long as an anomalous resistivity is assumed to increase with the relative electron-ion drift velocity