Dynamic current sheets with localized anomalous resistivity

Two-dimensional compressible magnetohydrodynamic simulations of current sheet dynamics under the influence of localized anomalous resistivity are presented. The system is initially perturbed by several spots of anomalous resistivity distributed in the sheet. Following a phase of induced tearing resulting from the initial perturbation, magnetic island coalescence occurs until one island persists. Finally the evolution becomes eruptive, dominated by the acceleration and ejection of a plasmoid, as a consequence of the amplification of a small initial asymmetry after a few 10(2) Alfven times. These processes are accompanied by strong enhancements of the current density. It exceeds the threshold of kinetic instability repeatedly and leads to recurrence of anomalous resistivity, which drives the evolution. Jets are formed, driven by held line reconnection and locally enhanced dissipation at dominant X-points. The conversion of magnetic energy into kinetic energy is most efficient during the acceleration phase of the plasmoid. The evolution becomes more impulsive and leads to stronger current density enhancements for higher Lundquist numbers. (C) 1996 American Institute of Physics.