Collisionless reconnection supported by nongyrotropic pressure effects in hybrid and particle simulations

This paper presents the detailed comparative analysis of full particle and hybrid simulations of collisionless magnetic reconnection. The comprehensiv e hybrid simulation code employed in this study incorporates essential elec tron kinetics in terms of the evolution of the full electron pressure tenso r in addition to the full ion kinetics and electron bulk flow inertia effec ts. As was demonstrated in our previous publications, the electron nongyrot ropic pressure effects play the dominant role in supporting the reconnectio n electric field in the immediate vicinity of the neutral X point. The simu lation parameters are chosen to match those of the Geospace Environmental M odeling (GEM) "Reconnection Challenge." It is that these comprehensive hybr id simulations perfectly reproduce the results of full particle simulations in many details. Specifically, the time evolutions of the reconnected magn etic flux and the reconnection electric field,, as well as spatial distribu tions of current density and magnetic field at all stages of the reconnecti on process, are found to be nearly identical for both simulations. Comparis ons of variations of characteristic quantities along the x and z axes cente red around the dominating X points also revealed a remarkable agreement. No ticeable differences are found only in electron temperature profiles, i.e., in the diagonal electron pressure tensor components. The deviation in the electron heating pattern in hybrid simulations from that observed in partic le simulations, However, does not affect parameters essential for the recon nection process. In particular, the profiles of the off-diagonal components of the electron pressure tensor are found to be very similar for both runs and appear unaffected by heat flux effects. Both simulations also demonstr ate that the E-y component of the electric field is nearly constant inside the diffusion region where ions are nonmagnetized. Wt: demonstrate that the simple analytical estimate for the reconnection electric field as a convec tion electric field at the edge of the diffusion region very well reproduce s the reconnection electric field observed in the simulations.