存在非均匀磁场时$f$模式的扇出
Fanning out of the $f$-mode in presence of nonuniform magnetic fields
摘要：
我们表明，在存在的谐波变化的磁场的基本或$f$ -模式中的分层改变，以这样一种方式，它扇出的诊断$kω$图，但模式功率也在风扇内。在我们的模拟中，表面被定义为在分段等温层中的温度和密度跳跃。与我们之前的工作（Singh等人，2014）不同，我们考虑了均匀磁场，在这里，我们采用了非均匀磁场以及长度尺度远小于磁场的磁流体湍流。$f$ -模式的扩展是较强的局限于表面以下的层的字段。在某些情况下，$kω$图还揭示了一类新的低频垂直条纹，其频率是背景磁场水平波数的两倍。我们认为，$f$模式展开的研究可能是一个新的和敏感的工具，以确定地下磁场的纵向周期性。
英文摘要：
We show that in the presence of a harmonically varying magnetic field the fundamental or $f$-mode in a stratified layer is altered in such a way that it fans out in the diagnostic $kω$ diagram, but with mode power also within the fan. In our simulations, the surface is defined by a temperature and density jump in a piecewise isothermal layer. Unlike our previous work (Singh et al. 2014) where a uniform magnetic field was considered, we employ here a nonuniform magnetic field together with hydromagnetic turbulence at length scales much smaller than those of the magnetic fields. The expansion of the $f$-mode is stronger for fields confined to the layer below the surface. In some of those cases, the $kω$ diagram also reveals a new class of low frequency vertical stripes at multiples of twice the horizontal wavenumber of the background magnetic field. We argue that the study of the $f$-mode expansion might be a new and sensitive tool to determining subsurface magnetic fields with longitudinal periodicity.
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