Reproducing the bipolar magnetic signature at the jet leading edge by three-dimensional reconnection with nonzero guide field

A bipolar (southward‐then‐northward) signature of the Bz component at the leading edge of earthward jets in the magnetotail has often been reported. Here we try to reproduce this magnetic field feature by a three‐dimensional reconnection (finite extent in the dawn‐dusk direction) in the presence of a nonzero guide field (dawn‐dusk magnetic component). Setting the guide field intensity by referring to earlier reports (Slavin et al., 2003) and setting the dawn‐dusk extent of the reconnection region to an often quoted value (Angelopoulos et al., 1997), we managed to reproduce the bipolar signatures in three‐dimensional (Hall) MHD simulation runs. Redirecting the argument, with the typical guide field intensity of By = 4 nT in the magnetotail, the southward peak value of Bz = −3 nT in the bipolar signature may be taken as the evidence that the dawn‐dusk width of the reconnection region is ∼4 RE (RE: Earth radii).