INTERCHANGE RECONNECTION IN A TURBULENT CORONA
INTERCHANGE RECONNECTION IN A TURBULENT CORONA
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DOI：
10.1088/2041-8205/758/1/l14
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发表时间：
2012-09
期刊：
影响因子：
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通讯作者：
A. Rappazzo;W. Matthaeus;D. Ruffolo;S. Servidio;M. Velli
中科院分区：
文献类型：
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作者：
A. Rappazzo;W. Matthaeus;D. Ruffolo;S. Servidio;M. Velli
日冕洞和环之间界面处的磁重联，即所谓的互换重联，可以将更热、更密的等离子体从磁约束区域释放到日光层中，从而有助于形成高度可变的慢太阳风。通常认为交换过程是在Y型和X型中性点附近的拖缆或伪拖缆的顶点处发展的，但最近沿着靠近封闭区域、远离顶点的扇状开放场线观察到具有环路组成的慢流。然而，磁力线因对流运动而打乱的日冕加热模型表明，在没有中性点的单极磁场区域中，重新连接可以连续发生：光球运动在日冕场中引起磁流体动力湍流级联，从而产生必要的小尺度，其中局部产生与强轴向场正交的剪切磁场分量，并且可以重新连接。我们提出类似的机制在开放区域和封闭区域之间的边界附近和周围运行，从而引起连通性的连续随机重新排列。我们研究了由强单极磁场穿过的开放和闭合日冕之间的简化界面区域的简化磁流体动力学模型。这个边界不是静止的，而是分形的，并且场线不断改变连通性，变得开放和封闭。该模型表明，慢风可能起源于环-冕洞边界区域的任何地方，并且可以自然而简单地解释这些边界处及其附近的流出以及观察到的日光层电流片周围慢风的扩散。
Magnetic reconnection at the interface between coronal holes and loops, the so-called interchange reconnection, can release the hotter, denser plasma from magnetically confined regions into the heliosphere, contributing to the formation of the highly variable slow solar wind. The interchange process is often thought to develop at the apex of streamers or pseudo-streamers, near Y- and X-type neutral points, but slow streams with loop composition have been recently observed along fanlike open field lines adjacent to closed regions, far from the apex. However, coronal heating models, with magnetic field lines shuffled by convective motions, show that reconnection can occur continuously in unipolar magnetic field regions with no neutral points: photospheric motions induce a magnetohydrodynamic turbulent cascade in the coronal field that creates the necessary small scales, where a sheared magnetic field component orthogonal to the strong axial field is created locally and can reconnect. We propose that a similar mechanism operates near and around boundaries between open and closed regions inducing a continual stochastic rearrangement of connectivity. We examine a reduced magnetohydrodynamic model of a simplified interface region between open and closed corona threaded by a strong unipolar magnetic field. This boundary is not stationary, becomes fractal, and field lines change connectivity continuously, becoming alternatively open and closed. This model suggests that slow wind may originate everywhere along loop–coronal-hole boundary regions and can account naturally and simply for outflows at and adjacent to such boundaries and for the observed diffusion of slow wind around the heliospheric current sheet.