Resolution of the 180° Ambiguity for Inverse Horizontal Magnetic Field Configurations
Resolution of the 180° Ambiguity for Inverse Horizontal Magnetic Field Configurations
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DOI：
10.1086/509062
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发表时间：
2007
期刊：
影响因子：
--
通讯作者：
Jing Li;T. Amari;Yuhong Fan
中科院分区：
文献类型：
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作者：
Jing Li;T. Amari;Yuhong Fan
太阳物理学中一个众所周知的问题是，对于磁场方向反转180°的情况，横向磁场方向的解是模糊的。在本文中，我们集中在三种方法来消除180°模糊适用于三个MHD模型。这些方法是（1）参考场法，（2）磁压梯度法，（3）磁场发散自由法。所有这三种方法都是非迭代的，方法2和3是分析和快速的。我们将这些方法应用于三个MHD平衡模型场：（1）来自Low的非线性无力磁场平衡的解析解，（2）来自Fan &吉布森的新兴扭曲磁通管的模拟，以及（3）来自Amari等人的通过弛豫达到的爆发前扭曲磁通绳平衡。我们测量了边界中“逆水平场”区域内方法的成功，其在数学上定义为B最小𝛁值Bz > 0。当这些区域与磁场中性线重叠时，它们被称为“秃斑”（BPs）或逆拓扑。我们最重要的结论是，磁发散自由的方法是远远超过其他两种方法在BPs中的成功。这种方法需要对垂直磁场进行第二级测量。由于高质量的多层磁图将在不久的将来上线，我们的工作表明，多层磁场测量将是非常可取的客观和成功地解决180°模糊问题。
A well-known problem in solar physics is that solutions for the transverse magnetic field direction are ambiguous with respect to a 180° reversal in the field direction. In this paper we focus on three methods for the removal of the 180° ambiguity applied to three MHD models. These methods are (1) the reference field method, (2) the method of magnetic pressure gradient, and (3) the magnetic field divergence-free method. All three methods are noniterative, and methods 2 and 3 are analytical and fast. We apply these methods to three MHD equilibrium model fields: (1) an analytical solution of a nonlinear force-free magnetic field equilibrium from Low, (2) a simulation of an emerging twisted flux tube from Fan & Gibson, and (3) a pre-eruptive twisted magnetic flux rope equilibrium reached by relaxation from Amari et al. We measure the success of methods within "inverse horizontal field" regions in the boundary, which are mathematically defined by B⊥ ∙ 𝛁⊥Bz > 0. When such regions overlap with the magnetic field neutral lines, they are known as "bald patches" (BPs) or inverse topology. Our most important conclusion is that the magnetic divergence-free method is far more successful than the other two methods within BPs. This method requires a second level of measurements of the vertical magnetic field. As high-quality multilevel magnetograms will come online in the near future, our work shows that multilayer magnetic field measurements will be highly desirable to objectively and successfully tackle the 180° ambiguity problem.