STANDING KINK MODES IN THREE-DIMENSIONAL CORONAL LOOPS
STANDING KINK MODES IN THREE-DIMENSIONAL CORONAL LOOPS
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DOI：
10.1088/0004-637x/784/2/101
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发表时间：
2014-03
期刊：
影响因子：
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通讯作者：
D. Pascoe;I. De Moortel
中科院分区：
文献类型：
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作者：
D. Pascoe;I. De Moortel
到目前为止，Edwin & Roberts提出的直通量管模型是实际日冕地震学中最常用的工具，特别是从观测到的固定扭结模式振荡中推断（日冕）磁场值。由于周期是地震反演中确定磁场的一个重要参数，本文将该基本模型预测的周期与三维稳态扭结模振荡数值模拟结果进行了比较。我们在直线和弯曲的三维日冕环中进行了固定扭结模式的数值模拟，并考虑了内部和外部驱动的激励。稠密日冕环位移的振荡周期由环长和扭结速度决定，与基于解析理论对直磁通管的估计一致。对于嵌入在磁拱廊中并由外部驱动器激励的弯曲日冕环，也存在由环路长度和外部alfv<s:1>速度决定周期的二次模式。当考虑到低频率的振荡时，这两个周期可能导致功率谱中出现一个单一的、不可分辨的（宽）峰值，特别是对于密度对比度较低的值，这两个周期将相对相似。在这种情况下（对于这种特殊的几何形状），这种附加模式的存在将导致对磁场强度的模糊地震学估计。
So far, the straight flux tube model proposed by Edwin & Roberts is the most commonly used tool in practical coronal seismology, in particular, to infer values of the (coronal) magnetic field from observed, standing kink mode oscillations. In this paper, we compare the period predicted by this basic model with three-dimensional (3D) numerical simulations of standing kink mode oscillations, as the period is a crucial parameter in the seismological inversion to determine the magnetic field. We perform numerical simulations of standing kink modes in both straight and curved 3D coronal loops and consider excitation by internal and external drivers. The period of oscillation for the displacement of dense coronal loops is determined by the loop length and the kink speed, in agreement with the estimate based on analytical theory for straight flux tubes. For curved coronal loops embedded in a magnetic arcade and excited by an external driver, a secondary mode with a period determined by the loop length and external Alfvén speed is also present. When a low number of oscillations is considered, these two periods can result in a single, non-resolved (broad) peak in the power spectrum, particularly for low values of the density contrast for which the two periods will be relatively similar. In that case (and for this particular geometry), the presence of this additional mode would lead to ambiguous seismological estimates of the magnetic field strength.