A magnetic reconnection X-line extending more than 390 Earth radii in the solar wind

Phan, T.D., J.T. Gosling, M.S. Davis, R.M. Skoug, M. Øieroset, R.P. Lepping, D.J. McComas, C.W. Smith, H. Reme, and A. Balogh

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 currant sheet embedded in the solar wind flow, where the reconnection X-line extended at least 390R_E or 2.5 x 10⁶km). Observations of this and 27 similar events imply that 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 external flow.

Nature, Letters, Vol 439|12 January 2006|doi:10.1038/nature04393, submitted, 2006