RESONANT ABSORPTION OF AXISYMMETRIC MODES IN TWISTED MAGNETIC FLUX TUBES
RESONANT ABSORPTION OF AXISYMMETRIC MODES IN TWISTED MAGNETIC FLUX TUBES
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DOI：
10.3847/0004-637x/823/2/71
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发表时间：
2016-05
期刊：
影响因子：
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通讯作者：
I. Giagkiozis;M. Goossens;G. Verth;V. Fedun;T. Doorsselaere
中科院分区：
文献类型：
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作者：
I. Giagkiozis;M. Goossens;G. Verth;V. Fedun;T. Doorsselaere
最近的研究表明，在太阳大气中普遍存在磁扭转和轴对称磁流体模式，因此研究这些模式的共振吸收成为一个紧迫的问题，因为它可以对太阳大气中的磁通管加热和观测到的衰减产生重要的影响。在本研究中，我们首次计算轴对称磁流体波在弱扭曲磁通管中的阻尼率。我们的目的是研究这些模式的共振衰减对太阳大气条件的影响。这一分析研究是基于直磁通管的理想化构型，管内和管外都有弱的磁扭矩。通过实施Sakurai等人推导的守恒定律。和Giagkiozis等人最近得到的弱扭曲磁通管的解析解。我们推导了Alfvén连续体谱中轴对称共振阻尼模的色散关系。我们还得到了长波长极限下阻尼率的一个有洞察力的解析表达式。此外，在非均匀层中允许纵向磁场和密度连续变化的情况下，对减振时间有显著影响。在太阳大气条件下，共振阻尼轴对称模式很可能无处不在，并在能量耗散中发挥重要作用。我们还认为，考虑到这些波的性质，它们很可能已经以阿尔芬波的名义被观测到了。
It has been shown recently that magnetic twist and axisymmetric MHD modes are ubiquitous in the solar atmosphere, and therefore the study of resonant absorption for these modes has become a pressing issue because it can have important consequences for heating magnetic flux tubes in the solar atmosphere and the observed damping. In this investigation, for the first time, we calculate the damping rate for axisymmetric MHD waves in weakly twisted magnetic flux tubes. Our aim is to investigate the impact of resonant damping of these modes for solar atmospheric conditions. This analytical study is based on an idealized configuration of a straight magnetic flux tube with a weak magnetic twist inside as well as outside the tube. By implementing the conservation laws derived by Sakurai et al. and the analytic solutions for weakly twisted flux tubes obtained recently by Giagkiozis et al. we derive a dispersion relation for resonantly damped axisymmetric modes in the spectrum of the Alfvén continuum. We also obtain an insightful analytical expression for the damping rate in the long wavelength limit. Furthermore, it is shown that both the longitudinal magnetic field and the density, which are allowed to vary continuously in the inhomogeneous layer, have a significant impact on the damping time. Given the conditions in the solar atmosphere, resonantly damped axisymmetric modes are highly likely to be ubiquitous and play an important role in energy dissipation. We also suggest that, given the character of these waves, it is likely that they have already been observed in the guise of Alfvén waves.