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arXiv 1104.1791astro-ph.SR
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共振吸收引起的弯折波的空间阻尼:背景流的影响

Spatial Damping of Propagating Kink Waves Due to Resonant Absorption: Effect of Background Flow

Roberto Soler, Jaume Terradas, Marcel Goossens

摘要:

观测表明,在太阳大气中普遍存在着传播的磁流体动力学(MHD)扭折波。波和流经常同时被观察到。由于等离子体在垂直于磁场的方向上的不均匀性,扭结波在空间上被共振吸收阻尼。流动的存在可能影响波的空间阻尼。本文研究了纵向背景流对横向非均匀磁通量管中共振扭折波的传播和空间阻尼的影响。我们结合近似分析理论与数值研究。分析理论使用薄管(TT)和薄边界(TB)近似,以获得波长和阻尼长度的表达式。数值上,我们验证了以前获得的解析表达式的电阻MHD本征值问题的全部解决方案的手段超越TT和TB近似。我们发现,向后和向前传播的波具有不同的波长和阻尼的长度尺度是成反比的频率在静态的情况下。然而,比例系数取决于流动的特性,因此阻尼长度不同于其静态模拟。对于缓慢的亚阿尔文流动,向后传播的波在比没有流动时更短的长度尺度上被阻尼,而对于向前传播的波,阻尼长度更长。波的不同性质取决于它们相对于背景流的传播方向,可以通过观测来检测,并且可以与地震学应用相关。

英文摘要:

Observations show the ubiquitous presence of propagating magnetohydrodynamic (MHD) kink waves in the solar atmosphere. Waves and flows are often observed simultaneously. Due to plasma inhomogeneity in the perpendicular direction to the magnetic field, kink waves are spatially damped by resonant absorption. The presence of flow may affect the wave spatial damping. Here, we investigate the effect of longitudinal background flow on the propagation and spatial damping of resonant kink waves in transversely nonuniform magnetic flux tubes. We combine approximate analytical theory with numerical investigation. The analytical theory uses the thin tube (TT) and thin boundary (TB) approximations to obtain expressions for the wavelength and the damping length. Numerically, we verify the previously obtained analytical expressions by means of the full solution of the resistive MHD eigenvalue problem beyond the TT and TB approximations. We find that the backward and forward propagating waves have different wavelengths and are damped on length scales that are inversely proportional to the frequency as in the static case. However, the factor of proportionality depends on the characteristics of the flow, so that the damping length differs from its static analogue. For slow, sub-Alfvenic flows the backward propagating wave gets damped on a shorter length scale than in the absence of flow, while for the forward propagating wave the damping length is longer. The different properties of the waves depending on their direction of propagation with respect to the background flow may be detected by the observations and may be relevant for seismological applications.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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