Phan T D, Gosling J T, Davis M S, Skoug R M, Øieroset M, Lin R P, Lepping R P, McComas D J, Smith C W, Reme H, Balogh A
Space Sciences Laboratory, University of California, Berkeley, California 94720, USA.
Nature. 2006 Jan 12;439(7073):175-8. doi: 10.1038/nature04393.
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.
电流片中的磁重联将磁能转化为粒子能量，这一过程在许多实验室、空间和天体物理环境中都很重要。目前尚不清楚磁重联从根本上来说是一个能在空间扩展区域发生的过程，还是本质上是零散且不可预测的。地球磁层中与磁重联相关的小规模通量绳和流道的频繁报告，增加了磁重联本质上是零散的可能性，即每个磁重联X线（相反方向的磁力线重新连接的线）最多延伸几个地球半径（R(E)），尽管相关的电流片跨度达数十或数百个R(E)。在此，我们报告了对与嵌入太阳风流动中的电流片中的磁重联相关的加速流的三航天器观测结果，其中磁重联X线至少延伸了390R(E)（或2.5×10^6千米）。对这一事件以及27个类似事件的观测表明，磁重联从根本上来说是一个大规模过程。因此，在地球磁层中观测到的零散磁重联很可能是与波动边界条件相关的地球物理效应，而非磁重联的基本属性。令人惊讶的是，我们的观测还揭示，即使在没有外部流动驱动的情况下，磁重联也能以准稳态方式运行。
