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Spontaneous non-steady reconnection within the framework of pure resistive magnetohydrodynamics: is anomalous resistivity really unescapable ?

Book Contribution - Book Chapter Conference Contribution

Can pure resistive magnetohydrodynamics reconnection within the solar environment be spontaneously fast and determine a final macroscopic turbulent state? Yes, it can. Several numerical experiments as well as analytical studies have suggested that within the pure resistive magnetohydrodynamics (MHD) framework it is not possible to have a magnetic field-line reconnecting dynamics that spontaneously evolves from a low and constant rate phase to a fast and high power regime. "Ad-hoc" terms derived from kinetic theory are used to resemble heuristically the non-trivial microscopic mechanisms determining the formation of an anomalous enhancement in plasma’s local resistivity that in turn triggers a fast MHD reconnection process. Here, we present both the complete numerical and geometrical analysis of the spontaneous non-steady MHD reconnection mechanism first discovered by Lapenta (2008) and the application of such model to the instability evolution of a current-sheet located in a medium with a strong density variation along the current layer. Hence, the effects of the global resistivity, the global viscosity and the plasma beta on the overall dynamics are considered. Such mechanism allows the transition from a slow to a self-feeding fast reconnection regime in MHD and it determines a final chaotic structure in a current-sheet whose global dynamics resembles the tearing evolution of solar structures both just before and immediately after observed and/or modeled explosive and bursty phenomena. Although we can not neglect the importance of anomalous effects to connect the small- and large-scale dynamics of plasma structures with the MHD-theory framework, the mechanism here presented would allow us to develop a consistent model for fast MHD reconnection within the solar environment.
Book: AGU Fall Meeting
Publication year:2009