Effect of different initialization methods on reconnection physics: A critical study using Hall MHD, hybrid, Hall-less hybrid and full particle simulations

Two commonly used techniques for performing reconnection simulations have been to either localize the resistivity (in simulations where electron kinetic effects are not included) or impose an external perturbation on the system. In MHD, it has been shown that depending on the spatial extent of resistivity, the nature of the solution changes. When resistivity region occupies a large fraction of simulation domain, one obtains a Sweet-Parker solution whereas in a localized resistivity case, the solution is Petschek-like. We demonstrate that this is due to the fact that in MHD the size of the diffusion region coincides with the region of localized resistivity. In non-MHD limit, this is no longer the case. In order to gain a better understanding of the effect of initialization on the physics of reconnection, we compare and contrast different initialization schemes, including new initialization procedure. We examine the reconnection details and the size of the diffusion region in four types of simulations codes: Hall MHD, hybrid (electron fluid, kinetic ions), Hall-less hybrid, and full particle simulations.