太阳耀斑期间环顶区域观测到的各向异性湍流

Xiaoyan Xie, Chengcai Shen, Katharine K. Reeves, Bin Chen, Xiaocan Li, Fan Guo, Sijie Yu, Yuqian Wei and Chuanfei Dong
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引用次数: 0

摘要

太阳耀斑环顶之上(ALT)区域对于理解太阳爆发和等离子体物理的基本过程至关重要。三维(3D)磁流体动力学(MHD)模拟的最新进展揭示了耀斑ALT区域湍流流动和MHD不稳定性的前所未有的细节。在这里,我们首次通过对从正面观察角度观察到的窄带极紫外图像应用流动跟踪算法来研究ALT中湍流的可观测各向异性特性。首先,定量地证实了前人的观察结果,即垂直运动占主导地位,各向异性流动在整个ALT区域广泛分布,并有上升和下降的贡献。(2)各向异性呈现高度依赖特征,ALT区域各向异性在一定的中间高度处表现最为明显,这与MHD模拟结果吻合较好,其中ALT区域湍流是由rayleigh - taylor型不稳定性引起的。最后,我们的发现表明,超级拱廊下流(SADs)是ALT地区最明显的动力结构,只是湍流的一个方面。在这些湍流中,我们还报告了可能由于MHD不稳定性而发展的反太阳移动的低密度流,正如以前的3D耀斑模型所建议的那样。我们的结果表明,整个耀斑扇表现出湍流的群体行为,其中观测到的明亮尖峰和相对较暗的SADs表现出相似的各向异性特征。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Anisotropic Turbulent Flows Observed in Above-the-loop-top Regions during Solar Flares
Solar flare above-the-loop-top (ALT) regions are vital for understanding solar eruptions and fundamental processes in plasma physics. Recent advances in three-dimensional (3D) magnetohydrodynamic (MHD) simulations have revealed unprecedented details on turbulent flows and MHD instabilities in flare ALT regions. Here, for the first time, we examine the observable anisotropic properties of turbulent flows in ALT by applying a flow-tracking algorithm on narrow-band extreme-ultraviolet images that are observed from the face-on viewing perspective. First, the results quantitatively confirm the previous observation that vertical motions dominate and that the anisotropic flows are widely distributed in the entire ALT region with the contribution from both upflows and downflows. Second, the anisotropy shows height-dependent features, with the most substantial anisotropy appearing at a certain middle height in ALT, which agrees well with the MHD modeling results where turbulent flows are caused by Rayleigh–Taylor-type instabilities in the ALT region. Finally, our finding suggests that supra-arcade downflows (SADs), the most prominently visible dynamical structures in ALT regions, are only one aspect of turbulent flows. Among these turbulent flows, we also report the antisunward-moving underdense flows that might develop due to MHD instabilities, as suggested by previous 3D flare models. Our results indicate that the entire flare fan displays group behavior of turbulent flows where the observational bright spikes and relatively dark SADs exhibit similar anisotropic characteristics.
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