Current sheet structure around the near-Earth neutral line observed by Geotail

[1] The current sheet structure around the near-Earth neutral line during substorms is investigated using ion and electron velocity moments directly obtained by the Geotail satellite. The intense cross-tail current sheet is found to be thinner closer to the X line and becomes as thin as 500 km. This is less than the ion inertial length ( 720 km), where ions are decoupled from electrons. The current sheet is found to be bifurcated from the ion diffusion region to the off-neutral sheet and forms a double-peaked current sheet away from the X line. Fast dawnward moving electrons with the strong ambipolar electric field toward the neutral sheet (E-ns) carry the intense electron-dominated current, and such E-ns is larger than E-y in the bursty bulk flows. So-called Hall current system into/out of the X line caused by the large separation between ion and electron motions is fully identified. The Hall current system is observed around the neutral sheet in the vicinity of the X line and bifurcates to the north/south boundary regions as the distance from the X line increases. There, the inward and outward currents form antiparallel current layers, whose boundaries are identified as 0.8 similar to 0.85 of lobe magnetic field intensity.