Detailed analysis of low-energy electron streaming in the near-Earth neutral line region during a substorm

A synaptic view of Cluster FGM, CIS, EDI, and PEACE observations of the near-Earth neutral line region during 1800-1830 UT on 13 September 2002 is discussed. Associated with the flow reversal and a thin cross-tail current sheet, a clear signature of a quadrupolar magnetic field is observed, which indicates the formation of the Hall current system around the X line in the large-scale picture. Associated with this magnetic field structure, low energy field-aligned electron beams mainly directed toward the X line are observed. High resolution data of FGM and EDI further show the fine structure of the low energy electron beams near the plasma sheet-lobe boundary. The beam becomes much more intense in the narrower region associated with the small magnetic field disturbances. In some cases, complicated bi-directional or oppositely directed beams are observed.