Magnetohydrodynamic Waves in an Asymmetric Magnetic Slab

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• 作者：Matthew Allcock ; Robert Erdélyi
• 关键词：Coronal seismology ; Magnetic fields ; photosphere ; Waves ; magnetohydrodynamic ; Waves ; modes
• 刊名：Solar Physics
• 出版年：2017
• 出版时间：February 2017
• 年：2017
• 卷：292
• 期：2
• 全文大小：1411KB
• 刊物类别：Physics and Astronomy
• 刊物主题：Astrophysics and Astroparticles; Atmospheric Sciences; Space Sciences (including Extraterrestrial Physics, Space Exploration and Astronautics);
• 出版者：Springer Netherlands
• ISSN：1573-093X
• 卷排序：292

文摘

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, i.e. 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.