Observational Signatures of Transverse Magnetohydrodynamic Waves and Associated Dynamic Instabilities in Coronal Flux Tubes
Observational Signatures of Transverse Magnetohydrodynamic Waves and Associated Dynamic Instabilities in Coronal Flux Tubes
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DOI：
10.3847/1538-4357/aa5eb2
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发表时间：
2017-02-20
影响因子：
4.9
通讯作者：
Yokoyama, T.
中科院分区：
文献类型：
--
作者：
Antolin, P.;De Moortel, I.;Yokoyama, T.
磁流体(MHD)波渗透到太阳大气中，构成潜在的日冕加热剂。然而，到目前为止探测到的海浪可能只是真实现有海浪能量的一小部分。探测不仅受到仪器的限制，而且还受到波过程的限制，波过程使波能在无法检测的空间尺度上局部化。在这项研究中，我们对垂直截面上温度变化均匀和非均匀的冕环中的驻留横向MHD波进行了三维MHD模拟和正演模拟。观察到的特征主要是开尔文-亥姆霍兹不稳定性(KHI)、共振吸收和相位混合的组合。在存在跨环温度梯度的情况下，我们发现，与对环边界和周围日冕更敏感的发射线相比，对环核敏感的发射线捕获了不同的特征，导致了KHI混合产生的异相强度和多普勒速度调制。在所有考虑的模型中，共同的特征包括在扭结周期的一半处的强度和环路宽度调制，精细的链状结构，在多普勒图上的特征箭头形结构，以及整个线在时间上加宽，特别是在环边。对于我们的模型，这些特征中的大多数可以在空间分辨率为033和光谱分辨率为25公里的S(-1)的情况下被捕获，尽管我们确实获得了对线宽的严重高估。共振吸收导致观测到的多普勒运动动能随着时间的推移而显著减少，这不能通过相位混合和KHI运动的线宽的相应增加来恢复。我们估计这个隐藏的波能是观测值的5-10倍。
Magnetohydrodynamic (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 localize the wave power in undetectable spatial scales. In this study, we conduct 3D MHD simulations and forward modeling 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 compared to those that are more sensitive to the loop boundary and the surrounding corona, leading to an out-of-phase intensity and Doppler velocity modulation produced by KHI mixing. In all of the considered models, common signatures include an intensity and loop width modulation at half the kink period, a fine strand-like structure, a characteristic arrow-shaped structure in the Doppler maps, and 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 and a spectral resolution of 25 km s(-1), although we do obtain severe over-estimation of the line width. 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 KHI motions. We estimate this hidden wave energy to be a factor of 5-10 of the observed value.