Magnetohydrodynamic Nonlinearities in Sunspot Atmospheres: Chromospheric Detections of Intermediate Shocks
Magnetohydrodynamic Nonlinearities in Sunspot Atmospheres: Chromospheric Detections of Intermediate Shocks
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DOI：
10.3847/1538-4357/ab7a90
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发表时间：
2020-03-20
影响因子：
4.9
通讯作者：
Giorgi, F.
中科院分区：
文献类型：
--
作者：
Houston, S. J.;Jess, D. B.;Giorgi, F.
太阳大气层内激波的形成仍然是少数几个可观测到的能量耗散的特征之一，这些能量耗散是由太阳表面附近产生的大量磁流体动力学波引起的。活动区观测提供了波行为及其对周围大气影响的特殊视图。在太阳低层大气中存在的分层等离子体梯度允许许多理论上的激波现象的潜在形成。在这项研究中，使用色球钙二λ 8542线光谱偏振数据的一个大的太阳黑子，我们研究波动的等离子体参数在强大的冲击事件，证明在其演变过程中的极化逆转的后果。采用现代反演技术来揭示与冲击形成同义的光学深度范围内发生的温度、视线速度和矢量磁场的扰动。这些非线性签名的分类进行了比较观测得出的慢，快，和阿尔芬冲击的理论朗肯-Hugoniot关系的解决方案。采用超过200，000个独立的测量，我们发现，阿尔芬（中间）冲击解决方案提供了最接近的理论和观测之间的匹配光学深度一致的几何高度之间的边界上光球层和较低的色球层。这项工作首次揭示了太阳黑子本影中色球层中间激波的证据，为一系列磁结构（包括孔隙、磁通绳和磁亮点）中波能的潜在热化提供了一种新方法。
The formation of shocks within the solar atmosphere remains one of the few observable signatures of energy dissipation arising from the plethora of magnetohydrodynamic waves generated close to the solar surface. Active region observations offer exceptional views of wave behavior and its impact on the surrounding atmosphere. The stratified plasma gradients present in the lower solar atmosphere allow for the potential formation of many theorized shock phenomena. In this study, using chromospheric Ca ii lambda 8542 line spectropolarimetric data of a large sunspot, we examine fluctuations in the plasma parameters in the aftermath of powerful shock events that demonstrate polarimetric reversals during their evolution. Modern inversion techniques are employed to uncover perturbations in the temperatures, line-of-sight velocities, and vector magnetic fields occurring across a range of optical depths synonymous with the shock formation. Classification of these nonlinear signatures is carried out by comparing the observationally derived slow, fast, and Alfven shock solutions with the theoretical Rankine-Hugoniot relations. Employing over 200,000 independent measurements, we reveal that the Alfven (intermediate) shock solution provides the closest match between theory and observations at optical depths of consistent with a geometric height at the boundary between the upper photosphere and lower chromosphere. This work uncovers first-time evidence of the manifestation of chromospheric intermediate shocks in sunspot umbrae, providing a new method for the potential thermalization of wave energy in a range of magnetic structures, including pores, magnetic flux ropes, and magnetic bright points.