Magnetic Reconnection Signatures in Near‐Earth Magnetotail Dipolarization Processes: Hall Electrons

Hall electrons, which are field‐aligned low‐energy (<1 keV) electrons flowing into the magnetic reconnection site, are detected in the tail lobe–plasma sheet boundary during dipolarization in the near‐Earth magnetotail at the onset of substorms. We examined 168 plasma sheet entry events in the magnetotail (up to 20 R E ) observed by the spacecraft Geotail in the period from 1995 to 2022. The results revealed that the Hall electrons were observed in a thin layer of the outermost plasma sheet, just outside the ion beam layer, during plasma sheet entries that were associated with dipolarization in the magnetic field at the onset of substorms. The initial east‐west magnetic field variations indicated the existence of earthward field‐aligned currents, which were consistent with the tailward flowing Hall electrons observed in the outermost plasma sheet.