Spatial Dimensions of the Electron Diffusion Region of Anti-Parallel Magnetic Reconnection

We systematically performed a series of high-resolution two-dimensional fully kinetic simulations to investigate spatial dimensions of the electron diffusion region of anti-parallel magnetic reconnection. In the electron diffusion region, electrons are demagnetized with the electron inertial and non-gyrotropic pressure effects. In the inflow direction, we found a clear two-scale structure of the diffusion region produced by the two effects. Both dimensions of the two-scale structure are proportional to the electron inertial length, but the dependence of the electron temperature is different between the two scales. In the outflow direction, we found no clear two-scale structure. The dimension in the outflow direction is proportional to the hybrid scale of ion and electron inertial lengths. The results allow us to predict the dimensions in realistic situations such as at the Earth's magentotail. The obtained predictions are indeed in reasonable agreement with past in-situ spacecraft observations at the magnetotail, and would have important implications for future in-situ observations with higher resolutions such as the NASA Magnetospheric Multiscale (MMS) mission.