Onset of magnetic reconnection in the presence of a normal magnetic field: Realistic ion to electron mass ratio

Two‐dimensional particle‐in‐cell simulations with a realistic ion to electron mass ratio are used to investigate the impact of an externally applied convection electric field on the stability of a moderately thick (1.6 c / ω pi ) current sheet configuration containing a nonzero B z . The imposition of the electric field produces a thinning of the current sheet associated with the formation of an embedded electron current layer and a reduction in the normal magnetic field component. The time scale for these processes is found to be nearly independent of the electron mass. Once k x ρ en becomes of order unity ( k x is the wave number for the maximally growing tearing mode, and ρ en is the electron gyroradius in the normal field), fluctuations drive B z southward over a subion‐inertia‐length scale region; further driving then leads to a conventional reconnection process featuring B z pulses (dipolarization fronts) propagating away from the X line. Consistent with earlier results with heavier electrons, strong parallel electric fields and an electron current layer form on scales of about an ion inertia length in the outflow direction, while electron outflow jets extend over much larger distances downstream from the X line.