title: Formation of inner structure of a reconnection separatrix region.
abstract: We present multipoint spacecraft observations at the dayside magnetopause of a magnetic reconnection separatrix region. This region separates two plasmas with significantly different temperatures and densities, at a large distance from the X line. We identify which terms in the generalized Ohm's law balance the observed electric field throughout the separatrix region. The electric field inside a thin approximately c/omega pi Hall layer is balanced by the j x B/ne term while other terms dominate elsewhere. On the low density side of the region we observe a density cavity which forms due to the escape of magnetospheric electrons along the newly opened field lines. The perpendicular electric field inside the cavity constitutes a potential jump of several kV. The observed potential jump and field aligned currents can be responsible for strong aurora.
authors.affiliation: Swedish Institute of Space Physics, Box 537, SE-751 21 Uppsala, Sweden.
authors.forename: Yu V
authors.initials: YV
authors.lastname: Khotyaintsev
authors.forename: A
authors.initials: A
authors.lastname: Vaivads
authors.forename: A
authors.initials: A
authors.lastname: Retinò
authors.forename: M
authors.initials: M
authors.lastname: André
authors.forename: C J
authors.initials: CJ
authors.lastname: Owen
authors.forename: H
authors.initials: H
authors.lastname: Nilsson