[论文解读] The chromospheric component of coronal bright points. Coronal and chromospheric responses to magnetic-flux emergence

M. S. Madjarska, Jongchul Chae+6 more|arXiv (Cornell University)|Jan 1, 2021

Solar and Space Plasma Dynamics参考文献 59被引用 15

一句话总结

本研究利用SDO和地面望远镜的多波段观测，调查了日冕亮斑（CBP）的色球层对应现象，发现色球层Hα环在日冕加热后响应延迟小于3分钟。研究结果表明，日冕加热先于色球层加热发生，支持磁重联与热传导驱动能量从日冕向色球层传输的机制。

ABSTRACT

Context. We investigate the chromospheric counterpart of small-scale coronal loops constituting a coronal bright point (CBP) and its response to a photospheric magnetic-flux increase accompanied by co-temporal CBP heating. Aims. The aim of this study is to simultaneously investigate the chromospheric and coronal layers associated with a CBP, and in so doing, provide further understanding on the heating of plasmas confined in small-scale loops. Methods. We used co-observations from the Atmospheric Imaging Assembly and Helioseismic Magnetic Imager on board the Solar Dynamics Observatory, together with data from the Fast Imaging Solar Spectrograph taken in the H α and Ca II 8542.1 Å lines. We also employed both linear force-free and potential field extrapolation models to investigate the magnetic topology of the CBP loops and the overlying corona, respectively. We used a new multi-layer spectral inversion technique to derive the temporal variations of the temperature of the H α loops (HLs). Results. We find that the counterpart of the CBP, as seen at chromospheric temperatures, is composed of a bundle of dark elongated features named in this work H α loops, which constitute an integral part of the CBP loop magnetic structure. An increase in the photospheric magnetic flux due to flux emergence is accompanied by a rise of the coronal emission of the CBP loops, that is a heating episode. We also observe enhanced chromospheric activity associated with the occurrence of new HLs and mottles. While the coronal emission and magnetic flux increases appear to be co-temporal, the response of the H α counterpart of the CBP occurs with a small delay of less than 3 min. A sharp temperature increase is found in one of the HLs and in one of the CBP footpoints estimated at 46% and 55% with respect to the pre-event values, also starting with a delay of less than 3 min following the coronal heating episode. The low-lying CBP loop structure remains non-potential for the entire observing period. The magnetic topological analysis of the overlying corona reveals the presence of a coronal null point at the beginning and towards the end of the heating episode. Conclusions. The delay in the response of the chromospheric counterpart of the CBP suggests that the heating may have occurred at coronal heights.

研究动机与目标

• 理解日冕亮斑（CBP）中小尺度日冕环的色球层对应现象及其对磁通量涌现的动态响应。
• 研究CBP中日冕加热、色球层活动与磁通量增加之间的时序关系。
• 通过分析温度与辐射变化的时序，确定加热是起源于日冕还是色球层。
• 利用力平衡场与势场外推法分析CBP的磁拓扑结构及其上覆日冕。
• 应用一种新型多层光谱反演技术，以高时间分辨率推导Hα环的温度演化。

提出的方法

• 结合SDO的日球大气成像仪（AIA）与日震磁像仪（HMI）数据，以及地面快速成像太阳光谱仪（FISS）在Hα与Ca ii 8542.1 Å波段的观测数据。
• 应用Chae等（2020）提出的新型多层光谱反演技术，推导Hα环中氢温度的时序演化。
• 采用线性力平衡场（LFFF）与势场外推模型，重建CBP及其上覆日冕的三维磁拓扑结构。
• 分析磁通量、日冕辐射（AIA 193 Å）以及色球层强度与多普勒速度的时序变化，以识别响应延迟。
• 通过磁力线拓扑分析，在加热事件期间识别出日冕中性点的存在。
• 对比日冕加热（AIA 193强度上升）、磁通量增加（HMI）与色球层响应（Hα与Ca ii线）的时序，推断能量传输机制。

实验结果

研究问题

• RQ1 日冕亮斑的色球层对应现象是什么？它如何响应日冕加热？
• RQ2 CBP中日冕加热与色球层加热起始之间是否存在时间延迟？
• RQ3 CBP环结构的磁拓扑是否支持磁重联或其他能量释放机制？
• RQ4 热传导与粒子束在加热CBP环色球层足点中起什么作用？
• RQ5 观测到的Hα环温度升高与日冕环的温度升高相比如何？

主要发现

• CBP的色球层对应现象由一组暗色、拉长的Hα环构成，这些环与磁环结构紧密相关。
• 由光球层磁通量涌现触发的日冕加热事件，随后在色球层产生响应，延迟小于3分钟。
• 一个Hα环表现出超过事件前水平46%的温度急剧上升，一个CBP足点温度上升55%，两者均在3分钟内启动。
• 低高度CBP环结构在整个观测期间保持非势场状态，表明磁能持续积累。
• 磁拓扑分析显示，在加热事件开始与结束时均存在日冕中性点，支持重联驱动的加热机制。
• 加热结束后约30分钟，色球层动力学（包括斑点与增强的下沉流）仍持续存在，表明能量持续沉积。