磁绳向ICME的渐进转换
Progressive transformation of a flux rope to an ICME
摘要：
行星际日冕物质抛射（ICMEs）对一个天文单位（AU）处的太阳风状况产生强烈的扰动。一个子集，称为磁云（MCs），是由扭曲的磁通绳形成的，这些磁通绳输送了大量的磁通量和螺旋度，这些磁通量和螺旋度在CME中释放。在距离太阳1 AU处，MCs的磁结构通常被建模为忽略它们在航天器穿越期间的膨胀。然而，在某些情况下，MC呈现显著的扩张。我们在这里提出了一个巨大的和显着扩大MC观察风航天器在2004年11月9日和10日的分析。在使用最小方差方法确定磁通绳的近似取向之后，我们使用直接方法精确地确定与其前后磁不连续性相关的云轴的取向。该方法考虑了入界分支和出界分支之间的方位磁通量的守恒，并且对于有限的碰撞参量（即，不一定是航天器轨迹和云轴之间的小距离）。此外，使用直接方法，我们发现，ICME是由一个磁通绳（MC），其次是一个扩展的相干磁区。考虑到先前较大的通量绳的存在，这些观测结果被解释为部分与其前方的环境重新连接。这些发现意味着，弹射磁通绳逐渐剥离的重联和转化为所观察到的ICME（与剩余磁通绳在前面的部分）。
英文摘要：
The solar wind conditions at one astronomical unit (AU) can be strongly disturbed by the interplanetary coronal mass ejections (ICMEs). A subset, called magnetic clouds (MCs), is formed by twisted flux ropes that transport an important amount of magnetic flux and helicity which is released in CMEs. At 1 AU from the Sun, the magnetic structure of MCs is generally modeled neglecting their expansion during the spacecraft crossing. However, in some cases, MCs present a significant expansion. We present here an analysis of the huge and significantly expanding MC observed by the Wind spacecraft during 9 and 10 November, 2004. After determining an approximated orientation for the flux rope using the minimum variance method, we precise the orientation of the cloud axis relating its front and rear magnetic discontinuities using a direct method. This method takes into account the conservation of the azimuthal magnetic flux between the in- and out-bound branches, and is valid for a finite impact parameter (i.e., not necessarily a small distance between the spacecraft trajectory and the cloud axis). Moreover, using the direct method, we find that the ICME is formed by a flux rope (MC) followed by an extended coherent magnetic region. These observations are interpreted considering the existence of a previous larger flux rope, which partially reconnected with its environment in the front. These findings imply that the ejected flux rope is progressively peeled by reconnection and transformed to the observed ICME (with a remnant flux rope in the front part).
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