[论文解读] Coronal hole boundaries evolution at small scales: II. XRT view Can small-scale outflows at CHBs be a source of the slow solar wind?

S. Subramanian, M. S. Madjarska+1 more|arXiv (Cornell University)|Feb 8, 2010

Solar and Space Plasma Dynamics参考文献 31被引用 41

一句话总结

本研究利用太阳观测卫星Hinode的XRT仪器获取的高时间分辨率X射线图像，研究冕洞边界处的小尺度动力学，发现70%的瞬态亮化现象表现出膨胀的磁环或准直的喷流，强烈表明开放磁场与闭合磁场之间发生了磁重联。这些喷流起源于X射线亮斑，被提出为太阳慢速风的重要来源。

ABSTRACT

We developed an automated procedure for the identification of transient brightenings in images from the X-ray telescope on-board Hinode taken with an Al Poly filter in the equatorial coronal holes, polar coronal holes, and the quiet Sun with and without transient coronal holes. We found that in comparison to the quiet Sun, the boundaries of coronal holes are abundant with brightening events including areas inside the coronal holes where closed magnetic field structures are present. The visual analysis of these brightenings revealed that around 70% of them in equatorial, polar and transient coronal holes and their boundaries show expanding loop structures and/or collimated outflows. In the quiet Sun only 30% of the brightenings show flows with most of them appearing to be contained in the solar corona by closed magnetic field lines. This strongly suggests that magnetic reconnection of co-spatial open and closed magnetic field lines creates the necessary conditions for plasma outflows to large distances. The ejected plasma always originates from pre-existing or newly emerging (at X-ray temperatures) bright points. The present study confirms our findings that the evolution of loop structures known as coronal bright points is associated with the small-scale changes of coronal hole boundaries. The loop structures show an expansion and eruption with the trapped plasma consequently escaping along the "quasi" open magnetic field lines. These ejections appear to be triggered by magnetic reconnection, e.g. the so-called interchange reconnection between the closed magnetic field lines (BPs) and the open magnetic field lines of the coronal holes. We suggest that these plasma outflows are possibly one of the sources of the slow solar wind.

研究动机与目标

• 利用高分辨率X射线成像技术，研究冕洞边界处的精细尺度动力学。
• 确定在冕洞边界处观测到的瞬态亮化现象的起源与性质。
• 评估冕洞边界处的小尺度喷流是否可对慢速太阳风产生贡献。
• 比较冕洞与宁静太阳区域亮化现象的频率与形态，以推断磁场拓扑结构的影响。
• 探讨开放与闭合磁力线之间的磁重联在触发等离子体喷流中的作用。

提出的方法

• 采用自动化检测算法，利用Al-Poly滤光片的Hinode XRT X射线图像识别瞬态亮化现象。
• 分析了多个观测任务中赤道冕洞（ECH）、极区冕洞（PCH）、瞬态冕洞（TCH）以及宁静太阳（QS）区域的数据。
• 通过人工目视检查，根据形态对亮化现象进行分类，包括膨胀磁环和准直喷流。
• 比较冕洞与宁静太阳区域喷流的发生频率，以评估磁场构型差异的影响。
• 追踪喷流的起源，发现其来自冕洞边界处的预存或新出现的X射线亮斑（BPs），这些亮斑处于日冕温度。
• 评估闭合磁环（BPs）与开放磁力线之间互换重联在驱动等离子体喷流中的作用。

实验结果

研究问题

• RQ1 与宁静太阳相比，冕洞边界处瞬态亮化现象的频率与形态如何？
• RQ2 冕洞边界处观测到的喷流是否表现出与磁重联一致的特征？
• RQ3 从冕洞边界亮斑喷出的等离子体是否可解释慢速太阳风的起源？
• RQ4 在以开放磁场为主导的区域（冕洞）与以闭合磁场为主导的区域（宁静太阳）中，亮化现象的物理特性有何差异？
• RQ5 X射线亮斑的出现是否与冕洞边界处喷流的启动存在相关性？

主要发现

• 在赤道冕洞、极区冕洞、瞬态冕洞及其边界处，70%的瞬态亮化现象表现出膨胀磁环结构或准直喷流，而宁静太阳区域仅占30%。
• 冕洞中大多数喷流未被闭合磁力线束缚，表明开放磁力线允许等离子体持续逃逸。
• 等离子体喷流起源于X射线亮斑，这些区域是开放与闭合磁力线之间发生磁重联的场所。
• 观测到的动力学特征与互换重联一致，即闭合磁环与开放磁力线重联，将被捕获的等离子体释放至日球层。
• 本研究证实，冕洞边界处小尺度磁环的演化与爆发由磁重联驱动，是慢速太阳风的合理来源。
• 研究结果支持如下假设：冕洞边界动力学，特别是亮斑处的磁重联，显著贡献于慢速太阳风的质量与能量输入。