Damping of Slow Surface Kink Modes in Solar Photospheric Waveguides Modeled by One-dimensional Inhomogeneities
Damping of Slow Surface Kink Modes in Solar Photospheric Waveguides Modeled by One-dimensional Inhomogeneities
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DOI：
10.3847/1538-4357/abd7f3
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发表时间：
2020-12
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通讯作者：
Shao-Xia Chen;Bo Li;T. Doorsselaere;M. Goossens;Hui Yu;M. Geeraerts
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作者：
Shao-Xia Chen;Bo Li;T. Doorsselaere;M. Goossens;Hui Yu;M. Geeraerts
鉴于最近人们对孔隙和太阳黑子本影中的磁流体动力（MHD）波的兴趣，我们通过对具有圆柱形不均匀性（包括均匀内部、均匀外部和其间的连续过渡层（TL））的太阳光球波导进行建模来检查慢表面扭结模式（SSKM）的阻尼。在线性、电阻、无重力 MHD 中执行本征模分析，我们的方法是理想化的，除其他外，我们的平衡仅在径向方向上构建。尽管如此，我们仍然可以同时解决两种阻尼机制，一种是欧姆电阻率，另一种是尖点和阿尔芬连续体中 SSKM 的谐振吸收。我们发现这两种机制的相对重要性敏感地取决于磁雷诺数（R m）。共振吸收是实际大 R m 值的唯一阻尼机制，并且尖点共振通常在阿尔芬共振中占主导地位，除非轴向波数位于观测相关范围的下端。我们还发现，仅当 TL 宽度与半径之比远小于名义预期时，薄边界近似才成立。对于实际较小的 R m，欧姆电阻率更为重要。即使在这种情况下，SSKM 也只是轻微阻尼，在我们检查的参数范围内，阻尼时间与周期之比达到~10。
Given the recent interest in magnetohydrodynamic (MHD) waves in pores and sunspot umbrae, we examine the damping of slow surface kink modes (SSKMs) by modeling solar photospheric waveguides with a cylindrical inhomogeneity comprising a uniform interior, a uniform exterior, and a continuous transition layer (TL) in between. Performing an eigenmode analysis in linear, resistive, gravity-free MHD, our approach is idealized in that, among other things, our equilibrium is structured only in the radial direction. We can nonetheless address two damping mechanisms simultaneously, one being the ohmic resistivity and the other being the resonant absorption of SSKMs in the cusp and Alfvén continua. We find that the relative importance of the two mechanisms depends sensitively on the magnetic Reynolds number (R m). Resonant absorption is the sole damping mechanism for realistically large values of R m, and the cusp resonance in general dominates the Alfvén one unless the axial wavenumbers are at the lower end of the observationally relevant range. We also find that the thin-boundary approximation holds only when the TL-width-to-radius ratios are much smaller than nominally expected. The ohmic resistivity is far more important for realistically small R m. Even in this case, SSKMs are only marginally damped, with damping-time-to-period ratios reaching ∼10 in the parameter range we examine.