Large Photospheric Doppler Shift in Solar Active Region 12673. I. Field-aligned Flows
Large Photospheric Doppler Shift in Solar Active Region 12673. I. Field-aligned Flows
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DOI：
10.3847/1538-4357/ace907
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发表时间：
2023-07
期刊：
影响因子：
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通讯作者：
J. Liu 刘;X. Sun 孙;P. Schuck;S. Jaeggli;B. Welsch;C. Noda
中科院分区：
文献类型：
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作者：
J. Liu 刘;X. Sun 孙;P. Schuck;S. Jaeggli;B. Welsch;C. Noda
δ (δ) 太阳黑子有时会沿着中心磁极反转线 (PIL) 出现快速光球流。在这里，我们研究了太阳活动区 NOAA 12673 中央半影光桥中的强多普勒频移特征。日震和磁成像仪 (HMI) 的观测表明存在高度剪切和强磁场。光桥形成过程中出现了高达 3.2 km s−1 的大多普勒频移，并持续了约 16 小时。一种名为 DAVE4VMwDV 的新型速度估计器可以从 HMI 矢量磁图揭示沿 PIL 的快速会聚和剪切运动，并且比旧版本的算法更好地恢复观察到的多普勒信号。推断的速度矢量很大程度上（反）平行于倾斜磁场，这表明观测到的多普勒频移包含来自投影场对齐流的显着贡献。 Hinode/Spectro-Polarimeter 的高分辨率观测进一步显示多普勒速度和磁倾角余弦之间存在明显的相关性，这与 HMI 结果一致，并且与约 9.6 km s−1 的场对准流一致。复杂的斯托克斯分布表明沿视线的物理变量存在显着的梯度。我们讨论了对 δ 点磁结构和流动驱动机制的影响。
Delta (δ) sunspots sometimes host fast photospheric flows along the central magnetic polarity inversion line (PIL). Here we study the strong Doppler shift signature in the central penumbral light bridge of solar active region NOAA 12673. Observations from the Helioseismic and Magnetic Imager (HMI) indicate highly sheared and strong magnetic fields. Large Doppler shifts up to 3.2 km s−1 appeared during the formation of the light bridge and persisted for about 16 hr. A new velocity estimator, called DAVE4VMwDV, reveals fast converging and shearing motion along the PIL from HMI vector magnetograms, and recovers the observed Doppler signal much better than an old version of the algorithm. The inferred velocity vectors are largely (anti-)parallel to the inclined magnetic fields, suggesting that the observed Doppler shift contains a significant contribution from the projected field-aligned flows. High-resolution observations from the Hinode/Spectro-Polarimeter further exhibit a clear correlation between the Doppler velocity and the cosine of the magnetic inclination, which is in agreement with HMI results and consistent with a field-aligned flow of about 9.6 km s−1. The complex Stokes profiles suggest significant gradients of physical variables along the line of sight. We discuss the implications on the δ-spot magnetic structure and the flow-driving mechanism.