Abstract
Physical conditions for the fast reconnection mechanism to be realized as an eventual solution of magnetohydrodynamic equations are examined by three-dimensional (3D) simulations for different resistivity models. Initiated by a small disturbance in a current sheet, all the phenomena grow by the self-consistent interaction between the 3D reconnection flow and the effective resistivity. For the classical resistivity η due to Coulomb collisions, where η∝T−3∕2, no effective reconnection occurs, since the resistivity becomes reduced with the increase in temperature T as magnetic reconnection proceeds, which indicates the negative feedback between the reconnection flow and the resistivity. For the anomalous resistivity, where η increases with the current density when a threshold is exceeded, the positive feedback eventually leads to the fast reconnection mechanism as a nonlinear instability. In this case, the resistivity is distinctly enhanced at the slow shock layer attached to the diffusion region, so that the shock layer becomes thicker, and resistive tearing is more likely to take place in the diffusion region. For the anomalous resistivity, where η increases with the relative electron-ion drift velocity when a threshold is exceeded, the fast reconnection mechanism evolves most effectively as a nonlinear instability and is sustained steadily. It is concluded in general three-dimensional situations that the fast reconnection mechanism can be realized as an eventual solution for current-driven anomalous resistivities, whereas in usual circumstances with the classical resistivity no substantial magnetic reconnection takes place.
Published Version
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