MHD wave transmission in the Sun’s atmosphere
MHD wave transmission in the Sun’s atmosphere
复制标题
太阳大气中的 MHD 波传输
DOI：
10.1051/0004-6361/201117356
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发表时间：
2011
影响因子：
6.5
通讯作者：
S. Jefferies
中科院分区：
文献类型：
--
作者：
M. Stangalini;D. Moro;F. Berrilli;S. Jefferies
MHD波在太阳大气层内的传播与磁场拓扑结构密切相关。例如，磁场能够降低声波的截止频率，从而允许原本被困在光球下面的波传播到上层大气中。另一个例子是，在声速等于阿尔芬速度的高度，MHD波可以传播或转化为其他形式的波。利用IBIS实验提供的大视场，研究了光球Fe 617.3 nm光谱线和色球Ca 854.2 nm光谱线采样的太阳大气中两个高度的波传播及其与局地磁场的关系。除其他外，我们发现在孔隙边缘的色球层及其周围的扩散磁场中有大量以5分钟为周期的波泄漏。通过对Hinode SOT/SP数据的光谱偏振反演，我们还发现了光球功率谱与磁场倾角之间的关系；在关节，明确的传输峰值约25◦为5分钟波和约15◦为3分钟波。我们提出了一个基于波传输理论的非常简单的模型来解释这种行为。最后，对功率谱和色球放大谱的分析表明，沿磁力线存在纵向声波。
MHD wave propagation inside the Sun's atmosphere is closely related to the magnetic field topology. For example, magneti c fields are able to lower the cutoff frequency for acoustic waves thus allowing waves which would otherwise be trapped below the photosphere to propagate into the upper atmosphere. Another example is that MHD waves can be transmitted or converted into other forms of waves at altitudes where the sound speed equals the Alfven speed. We take advantage of the large field-of-view provided b y the IBIS experiment to study the wave propagation at two heights in the solar atmosphere, as sampled by the photospheric Fe 617.3 nm spectral line and the chromospheric Ca 854.2 nm spectral line, and its relationship to the local magneti c field. Among other things, we find substantial leakage of waves with 5-minute periods in the chromosphere at the edges of a pore and in the diffused magnetic field surrounding it. By using spectro-polarimetric inversions of Hinode SOT/SP data, we also find a relationship between the photospheric power spectrum and the magnetic field inclination angle; in p articular, well-defined transmission peaks around 25 ◦ for 5 minutes waves and around 15 ◦ for 3 minutes waves. We propose a very simple model based upon wave transmission theory to explain this behavior. Finally, an analysis of both the power spectra and chromospheric amplification spectra suggests the presence of longitudinal acoustic waves along the magnetic field lines.