What Causes the High Apparent Speeds in Chromospheric and Transition Region Spicules on the Sun?
What Causes the High Apparent Speeds in Chromospheric and Transition Region Spicules on the Sun?
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DOI：
10.3847/2041-8213/aa9272
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发表时间：
2017-10
期刊：
影响因子：
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通讯作者：
B. De Pontieu;J. Martínez-Sykora;G. Chintzoglou
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文献类型：
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作者：
B. De Pontieu;J. Martínez-Sykora;G. Chintzoglou
针状体是太阳大气中最普遍的喷流类型。来自界面区域成像光谱仪（IRIS）和地面观测站的高分辨率成像和光谱学的出现，揭示了在天空平面上测量的针状体中存在100-300 km s−1的非常高的表观运动。然而，如此高速的视线测量很难获得，从谱线的多普勒频移推断的值通常为30-70 km s - 1。在这项工作中，我们利用最近的2.5D辐射MHD模拟解决了这一长期存在的差异。该模拟揭示了一种新的针状体驱动机制，其中由离子中性相互作用引起的双极性扩散起着关键作用。在我们的模拟中，我们经常看到来自低色球的电磁波和电流向上传播到已经存在的针状体中，当电流通过双极扩散迅速消散时，会导致快速加热。快速加热和这些电流以超过100 km / s−1的阿尔夫萨奇速度传播的结合导致了在色球和过渡区温度下针状体的非常快速的表观运动，并且经常是整体出现。在我们的模拟中，在这样的射流中观察到的快速表观运动实际上是一个加热锋的特征，并且比质量流高得多，后者的数量级为30-70 km s - 1。我们的研究结果可以解释过渡区“网络喷流”的行为和一些色球针状体极高的表观速度。
Spicules are the most ubuiquitous type of jets in the solar atmosphere. The advent of high-resolution imaging and spectroscopy from the Interface Region Imaging Spectrograph (IRIS) and ground-based observatories has revealed the presence of very high apparent motions of order 100–300 km s−1 in spicules, as measured in the plane of the sky. However, line of sight measurements of such high speeds have been difficult to obtain, with values deduced from Doppler shifts in spectral lines typically of order 30–70 km s−1. In this work, we resolve this long-standing discrepancy using recent 2.5D radiative MHD simulations. This simulation has revealed a novel driving mechanism for spicules in which ambipolar diffusion resulting from ion-neutral interactions plays a key role. In our simulation, we often see that the upward propagation of magnetic waves and electrical currents from the low chromosphere into already existing spicules can lead to rapid heating when the currents are rapidly dissipated by ambipolar diffusion. The combination of rapid heating and the propagation of these currents at Alfvénic speeds in excess of 100 km s−1 leads to the very rapid apparent motions, and often wholesale appearance, of spicules at chromospheric and transition region temperatures. In our simulation, the observed fast apparent motions in such jets are actually a signature of a heating front, and much higher than the mass flows, which are of order 30–70 km s−1. Our results can explain the behavior of transition region “network jets” and the very high apparent speeds reported for some chromospheric spicules.