Hall magnetohydrodynamic effects for three‐dimensional magnetic reconnection with finite width along the direction of the current

Abstract

We performed three‐dimensional Hall magnetohydrodynamic (MHD) simulations of magnetic reconnection with finite width along the direction perpendicular to the antiparallel magnetic field (i.e., the direction of the electric current). Previous similar simulations including the Hall term have shown that the localized reconnection region itself can broaden in the anticurrent direction when the initial current is carried only by electrons. However, there is still no clear understanding of the behavior of the reconnection region in the presence of the initial ion current as in the Earth's magnetotail plasma sheet since no simulations have been carried out under such situations. In this study, we performed a systematic parametric survey considering the cases in which the initial current is carried not only by electrons but also by ions and found that the speed and direction of the current‐aligned broadening of the reconnection region are almost equal to those of background ion and electron flows that carry the current. This result means that location and size of the localized reconnection region vary with time, depending on plasma conditions in the background current sheet in Hall MHD regime. The rate of the localized reconnection can reach close to the value in the two‐dimensional case, even when reconnection starts in an extremely narrow region with its current‐aligned width equal to an ion inertial length. The localized reconnection process also produces the asymmetry of the current‐aligned structure of the reconnection jet. These results can explain various observational features related to magnetic reconnection in the near‐Earth magnetotail.