抄録
Understanding the generation mechanisms of intense field-aligned currents (FACs) during auroral substorms is one of the central themes of magnetospheric physics. Three-dimensional (3D) magnetohydrodynamic (MHD) simulations of the Earth's magnetotail reconnection has been performed extensively to understand the global aspects of the generation mechanisms. In this study, however, by noting that the ion inertia length is not negligibly small compared to the current sheet thickness in the magnetotail, we investigate the FAC generation mechanism in the Hall-MHD system. With an idealized one-dimensional current sheet as the initial condition, we find that the FAC pattern obtained to be totally different from the MHD results. From a series of simulations, we also find that the predominance of this new FAC pattern is not necessarily due to the small thickness of the current sheet but is controlled more by the three-dimensionality of the system. The Hall-driven FAC dominates as long as the system is more two-dimensional-like than a critical value even for a relatively thick current sheet. Since this critical value turns out to be moderate, we conclude that reconnection in the Earth's magnetotail belongs to a general class of reconnection involving strong FACs generated by the Hall term.
