arXiv 1702.007752017-02-02astro-ph.SR

横向MHD波的观测特征和相关的动力不稳定性

Observational signatures of transverse MHD waves and associated dynamic instabilities

Patrick Antolin, Ineke De Moortel, Tom Van Doorsselaere, Takaaki Yokoyama

备注：: 24 pages, 19 figures. Accepted for publication in ApJ. In this ArXiv version, some of the figures have reduced quality due to size limits

摘要：

MHD波渗透太阳大气层，构成潜在的日冕加热剂。然而，迄今为止探测到的波浪可能只是真实存在的波浪能量的一小部分。检测是有限的仪器的限制，但也由波的过程，本地化的波功率在不可检测的空间尺度。在这项研究中，我们进行三维MHD模拟和正向模拟的冠环均匀和不均匀的温度变化的垂直截面的横向MHD驻波。所观察到的签名主要是由开尔文-亥姆霍兹不稳定性（KHI），共振吸收和相位混合的组合。在存在的交叉环温度梯度，我们发现，发射线敏感的环路核心捕捉不同的签名比那些更敏感的环路边界和周围的电晕，导致异相的强度调制所产生的KHI混合。所有考虑模型的共同签名包括在扭结周期的一半处的强度和环路宽度调制、细股状结构、多普勒图中的特征箭头形结构、时间上的整体线加宽，但特别是在环路边缘处。对于我们的模型，大部分这些功能可以捕获的空间分辨率为$0.33\arcsec$和光谱分辨率为25 km~s $^{-1}$，虽然严重高估的线宽。共振吸收导致从多普勒运动观察到的动能随着时间的推移显着减少，这是不能恢复的相混合和KHI运动的线宽的相应增加。我们估计这个隐藏的波能量是观测值的$5-10$的一个因子。

英文摘要：

MHD waves permeate the solar atmosphere and constitute potential coronal heating agents. Yet, the waves detected so far may be but a small subset of the true existing wave power. Detection is limited by instrumental constraints, but also by wave processes that localise the wave power in undetectable spatial scales. In this study we conduct 3D MHD simulations and forward modelling of standing transverse MHD waves in coronal loops with uniform and non-uniform temperature variation in the perpendicular cross-section. The observed signatures are largely dominated by the combination of the Kelvin-Helmholtz instability (KHI), resonant absorption and phase mixing. In the presence of a cross-loop temperature gradient we find that emission lines sensitive to the loop core catch different signatures than those more sensitive to the loop boundary and the surrounding corona, leading to an out-of-phase intensity modulation produced by the KHI mixing. Common signatures to all considered models include an intensity and loop width modulation at half the kink period, fine strand-like structure, a characteristic arrow-shaped structure in the Doppler maps, overall line broadening in time but particularly at the loop edges. For our model, most of these features can be captured with a spatial resolution of $0.33\arcsec$ and spectral resolution of 25~km~s$^{-1}$, although severe over-estimation of the line width is obtained. Resonant absorption leads to a significant decrease of the observed kinetic energy from Doppler motions over time, which is not recovered by a corresponding increase in the line width from phase mixing and the KHI motions. We estimate this hidden wave energy to be a factor of $5-10$ of the observed value.

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摘要：

英文摘要：

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