title: A magnetic reconnection X-line extending more than 390 Earth radii in the solar wind.
abstract: Magnetic reconnection in a current sheet converts magnetic energy into particle energy, a process that is important in many laboratory, space and astrophysical contexts. It is not known at present whether reconnection is fundamentally a process that can occur over an extended region in space or whether it is patchy and unpredictable in nature. Frequent reports of small-scale flux ropes and flow channels associated with reconnection in the Earth's magnetosphere raise the possibility that reconnection is intrinsically patchy, with each reconnection X-line (the line along which oppositely directed magnetic field lines reconnect) extending at most a few Earth radii (R(E)), even though the associated current sheets span many tens or hundreds of R(E). Here we report three-spacecraft observations of accelerated flow associated with reconnection in a current sheet embedded in the solar wind flow, where the reconnection X-line extended at least 390R(E) (or 2.5 x 10(6) km). Observations of this and 27 similar events imply that reconnection is fundamentally a large-scale process. Patchy reconnection observed in the Earth's magnetosphere is therefore likely to be a geophysical effect associated with fluctuating boundary conditions, rather than a fundamental property of reconnection. Our observations also reveal, surprisingly, that reconnection can operate in a quasi-steady-state manner even when undriven by the external flow.
authors.affiliation: Space Sciences Laboratory, University of California, Berkeley, California 94720, USA. phan@ssl.berkeley.edu
authors.forename: T D
authors.initials: TD
authors.lastname: Phan
authors.forename: J T
authors.initials: JT
authors.lastname: Gosling
authors.forename: M S
authors.initials: MS
authors.lastname: Davis
authors.forename: R M
authors.initials: RM
authors.lastname: Skoug
authors.forename: M
authors.initials: M
authors.lastname: Øieroset
authors.forename: R P
authors.initials: RP
authors.lastname: Lin
authors.forename: R P
authors.initials: RP
authors.lastname: Lepping
authors.forename: D J
authors.initials: DJ
authors.lastname: McComas
authors.forename: C W
authors.initials: CW
authors.lastname: Smith
authors.forename: H
authors.initials: H
authors.lastname: Reme
authors.forename: A
authors.initials: A
authors.lastname: Balogh