Allcock Matthew, Erdélyi Robert
Solar Physics and Space Plasma Research Centre, School of Mathematics and Statistics, University of Sheffield, Hicks Building, Hounsfield Road, Sheffield, S3 7RH UK.
Sol Phys. 2017;292(2):35. doi: 10.1007/s11207-017-1054-y. Epub 2017 Feb 1.
Analytical models of solar atmospheric magnetic structures have been crucial for our understanding of magnetohydrodynamic (MHD) wave behaviour and in the development of the field of solar magneto-seismology. Here, an analytical approach is used to derive the dispersion relation for MHD waves in a magnetic slab of homogeneous plasma enclosed on its two sides by non-magnetic, semi-infinite plasma with different densities and temperatures. This generalises the classic magnetic slab model, which is symmetric about the slab. The dispersion relation, unlike that governing a symmetric slab, cannot be decoupled into the well-known sausage and kink modes, the modes have mixed properties. The eigenmodes of an asymmetric magnetic slab are better labelled as quasi-sausage and quasi-kink modes. Given that the solar atmosphere is highly inhomogeneous, this has implications for MHD mode identification in a range of solar structures. A parametric analysis of how the mode properties (in particular the phase speed, eigenfrequencies, and amplitudes) vary in terms of the introduced asymmetry is conducted. In particular, avoided crossings occur between quasi-sausage and quasi-kink surface modes, allowing modes to adopt different properties for different parameters in the external region.
太阳大气磁结构的分析模型对于我们理解磁流体动力学（MHD）波行为以及太阳磁地震学领域的发展至关重要。在此，采用一种分析方法来推导均匀等离子体磁板中MHD波的色散关系，该磁板两侧被具有不同密度和温度的非磁性半无限等离子体包围。这推广了关于磁板对称的经典磁板模型。与对称磁板的色散关系不同，该色散关系不能解耦为众所周知的腊肠模和扭结模，这些模式具有混合特性。非对称磁板的本征模更好地标记为准腊肠模和准扭结模。鉴于太阳大气高度不均匀，这对一系列太阳结构中的MHD模式识别有影响。对模式特性（特别是相速度、本征频率和振幅）如何随引入的不对称性变化进行了参数分析。特别是，准腊肠模和准扭结表面模之间会出现避免交叉，使得模式在外部区域对于不同参数具有不同特性。
