日冕洞和安静太阳之间的异同：环统计是关键吗？
Similarities and Differences between Coronal Holes and the Quiet Sun: Are Loop Statistics the Key?
摘要：
日冕洞（CH）在日冕温度下的发射量明显低于安静太阳区域（QS），但在大多数色球层和低过渡区线中几乎无法区分。理解这种现象的一个关键量是磁场。我们利用SOHO/MDI的观测数据，借助于位磁模型，重建了冕洞和宁静太阳的磁场。从太阳表面上的规则网格开始，然后跟踪场线，其提供3D磁场结构的整体几何形状。我们区分开放和封闭的磁力线，与封闭的磁力线被假定为代表磁回路。然后，我们试图计算日冕环的一些性质。冕洞（CH）中的环平均比QS中的环平坦。高的和长的闭合环是非常罕见的，而短的和低的环在日冕洞中几乎和安静的太阳一样丰富。当解释环标度律的光，这一结果表明，相对较强的色球和过渡区的发射（许多低洼，短环），但弱的日冕发射（少数高，长环）在冕洞的解释。尽管这种对比，我们的计算还表明，一个显着的一部分冷排放CHs来自开放的通量区域。尽管磁场线统计提供了这些见解，但还需要进一步的工作来获得一个明确的答案，如果环统计解释冕洞和安静的太阳之间的差异。
英文摘要：
Coronal holes (CH) emit significantly less at coronal temperatures than quiet-Sun regions (QS), but can hardly be distinguished in most chromospheric and lower transition region lines. A key quantity for the understanding of this phenomenon is the magnetic field. We use data from SOHO/MDI to reconstruct the magnetic field in coronal holes and the quiet Sun with the help of a potential magnetic model. Starting from a regular grid on the solar surface we then trace field lines, which provide the overall geometry of the 3D magnetic field structure. We distinguish between open and closed field lines, with the closed field lines being assumed to represent magnetic loops. We then try to compute some properties of coronal loops. The loops in the coronal holes (CH) are found to be on average flatter than in the QS. High and long closed loops are extremely rare, whereas short and low-lying loops are almost as abundant in coronal holes as in the quiet Sun. When interpreted in the light of loop scaling laws this result suggests an explanation for the relatively strong chromospheric and transition region emission (many low-lying, short loops), but the weak coronal emission (few high and long loops) in coronal holes. In spite of this contrast our calculations also suggest that a significant fraction of the cool emission in CHs comes from the open flux regions. Despite these insights provided by the magnetic field line statistics further work is needed to obtain a definite answer to the question if loop statistics explain the differences between coronal holes and the quiet Sun.
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