arXiv 2009.083012020-09-17astro-ph.SR

编织磁场中MHD波的正演模拟

Forward Modelling of MHD Waves in Braided Magnetic Fields

Lianne Fyfe, Thomas Howson, Ineke De Moortel

备注：: 15 pages and 22 figures
发表信息：: A&A 643, A86 (2020)
DOI：: 10.1051/0004-6361/202038945

摘要：

瞄准我们调查合成观测签名产生的数值模型中传播的横波编织磁场。方法.我们研究了两个模拟与不同水平的磁场编织，并施加一个周期性的，横波司机在较低的边界。波浪反射离开顶部边界后，形成复杂的波浪干涉图案。我们分析的合成排放所产生的正演模拟代码，FoMo。我们检查线强度，多普勒频移和动能沿几个视线（LOS）的角度。结果多普勒频移表明存在横波。然而，当分析强度时，对于更复杂的磁场，波不太容易被观察到，并且可能被误认为是背景噪声。取决于LOS角，波的可观测特征反映了一些磁场编织，特别是当多个发射线可用时。在更多的编织模拟中，可以识别相混合的特征。我们确定可能的模糊性的解释波模式的基础上的合成发射签名。结论.本文中的大多数观测值都符合预期，因为我们知道3D空间中参数的演化。然而，一些有趣的观测签名是存在的。当存在波时，检测磁场复杂性的区域在某种程度上是可能的。然而，同时从不同的线光谱成像是重要的，以确定这些位置。在将强度和多普勒速度特征解释为扭转运动时需要小心，因为在我们的设置中，这种特征是磁场复杂性的结果，而不是扭转波。最后，用多普勒速度估计的动能取决于波的偏振、背景场的复杂性和LOS。

英文摘要：

Aim. We investigate synthetic observational signatures generated from numerical models of transverse waves propagating in braided magnetic fields. Methods. We examine two simulations with different levels of magnetic field braiding and impose a periodic, transverse wave driver at the lower boundary. After waves reflect off the top boundary, a complex pattern of wave interference forms. We analyse the synthetic emission produced by the forward modelling code, FoMo. We examine line intensity, Doppler shifts and kinetic energy along several line-of-sight (LOS) angles. Results. The Doppler shifts showed the presence of transverse waves. However, when analysing the intensity, waves are less easily observed for more complex magnetic fields and may be mistaken for background noise. Depending on the LOS angle, the observable signatures of waves reflect some of the magnetic field braiding, particularly when multiple emission lines are available. In the more braided simulation, signatures of phase mixing can be identified. We identify possible ambiguities in the interpretation of wave modes based on the synthetic emission signatures. Conclusions. Most of the observables within this article behave as expected, given knowledge of the evolution of the parameters in 3D space. However, some intriguing observational signatures are present. Detecting regions of magnetic field complexity is somewhat possible when waves are present. However, simultaneous spectroscopic imaging from different lines is important to identify these locations. Care needs to be taken when interpreting intensity and Doppler velocity signatures as torsional motions as, in our setup, such signatures were a consequence of the magnetic field complexity and not torsional waves. Finally, the kinetic energy, estimated with Doppler velocities, is dependent on the polarisation of the wave, complexity of the background field and the LOS.

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