Propagating Alfvénic Waves Observed in the Chromosphere around a Small Sunspot: Tales of 3-minute Waves and 10-minute Waves
Propagating Alfvénic Waves Observed in the Chromosphere around a Small Sunspot: Tales of 3-minute Waves and 10-minute Waves
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DOI：
10.3847/1538-4357/ac722e
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发表时间：
2022-07
期刊：
影响因子：
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通讯作者：
J. Chae;Kyuhyoun Cho;E. Lim;Juhyung Kang
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文献类型：
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作者：
J. Chae;Kyuhyoun Cho;E. Lim;Juhyung Kang
最近的观测提供了证据，证明太阳黑子区域的色球层充满了阿尔夫文波-横向磁流体动力学（MHD）波（阿尔夫文波或扭结波）。为了系统地研究Alfvénic波在较宽周期范围内的物理特征，我们分析了由位于大熊星座的Goode太阳望远镜的快速成像太阳光谱仪拍摄的一个小黑子区的Hα光谱数据所构造的视向速度图的时间序列。我们通过检查位于同一磁力线上的两个点之间的带通速度的互相关来识别每个阿尔夫维尼克波包。结果，我们在太阳黑子周围的超半影区共检测到279个波包，并获得了它们的周期、速度振幅和传播速度的统计数据。我们的一个重要发现是，检测到的Alfvénic波明显分为两组：3分钟周期（7分钟）波。我们提出了两种关于色球层中Alfvénic波起源的说法：3分钟的Alfvénic波是由色球层中向上传播的慢波通过慢波到Alfvénic模的转换激发的，而10分钟的Alfvénic波代表了光球层中对流运动驱动的扭结波的色球表现。
Recent observations provided evidence that the solar chromosphere of sunspot regions is pervaded by Alfvénic waves—transverse magnetohydrodynamic (MHD) waves (Alfvén waves or kink waves). In order to systematically investigate the physical characteristics of Alfvénic waves over a wide range of periods, we analyzed the time series of line-of-sight velocity maps constructed from the Hα spectral data of a small sunspot region taken by the Fast Imaging Solar Spectrograph of the Goode Solar Telescope at Big Bear. We identified each Alfvénic wave packet by examining the cross-correlation of band-filtered velocity between two points that are located a little apart presumably on the same magnetic field line. As result, we detected a total of 279 wave packets in the superpenumbral region around the sunspot and obtained their statistics of period, velocity amplitude, and propagation speed. An important finding of ours is that the detected Alfvénic waves are clearly separated into two groups: 3-minute period (7 minutes) waves. We propose two tales on the origin of Alfvénic waves in the chromosphere; the 3-minute Alfvénic waves are excited by the upward-propagating slow waves in the chromosphere through the slow-to-Alfvénic mode conversion, and the 10-minute Alfvénic waves represent the chromospheric manifestation of the kink waves driven by convective motions in the photosphere.