Three-dimensional spontaneous magnetic reconnection in neutral current sheets

Magnetic reconnection in an antiparallel uniform Harris current sheet equil ibrium, which is initially perturbed by a region of enhanced resistivity li mited in all three dimensions, is investigated through compressible magneto hydrodynamic simulations. Variable resistivity, coupled to the dynamics of the plasma by an electron-ion drift velocity criterion, is used during the evolution. A phase of magnetic reconnection amplifying with time and leadin g to eruptive energy release is triggered only if the initial perturbation is strongly elongated in the direction of current flow or if the threshold for the onset of anomalous resistivity is significantly lower than in the c orresponding two-dimensional case. A Petschek-like configuration is then bu ilt up for similar to 10(2) Alfven times, but remains localized in the thir d dimension. Subsequently, a change of topology to an O-line at the center of the system ("secondary tearing'') occurs. This leads to enhanced and tim e-variable reconnection, to a second pair of outflow jets directed along th e O-line, and to expansion of the reconnection process into the third dimen sion. High parallel current density components are created mainly near the region of enhanced resistivity. (C) 2000 American Institute of Physics. [S1 070-664X(00)00101-4].