论文标题
由扭转抗体驱动的非均匀冠状环的湍流过渡。 ii。磁性的扩展分析和效果
Transition to turbulence in nonuniform coronal loops driven by torsional Alfvén waves. II. Extended analysis and effect of magnetic twist
论文作者
论文摘要
在先前的工作中已经显示，扭转拟南芥可以用纯轴向磁场驱动不均匀的冠状环中的湍流。在这里，我们探索磁性扭曲的作用。我们将冠状环将冠状动脉循环模拟为横向不均匀的直磁管，锚定在光球中，并嵌入在均匀的冠状环境中。我们认为磁场是扭曲的，并通过模型的自由参数来控制磁扭转的强度。我们激发了站立扭转alfvén波的纵向基本模式，其时间的演化是通过高分辨率三维理想磁流失动力学数值模拟获得的。我们发现，扭转Alfvén波的相混合会在垂直于磁场线的方向上产生速度剪切。速度剪切最终触发了开尔文 - 赫尔姆霍尔茨不稳定性（KHI）。在弱扭曲的磁管中，KHI能够非线性生长，随后，湍流以与未透视的情况相似的方式在冠状环中驱动。只要磁性扭转仍然弱，磁性扭转的效果就是延迟KHI的发作并减慢湍流的发展。相比之下，即使磁性扭曲足够强，磁张力也可以抑制KHI的非线性生长，即使KHI已被相结合剪切局部激发。因此，在强扭曲的环中不会产生湍流
It has been shown in a previous work that torsional Alfvén waves can drive turbulence in nonuniform coronal loops with a purely axial magnetic field. Here we explore the role of the magnetic twist. We model a coronal loop as a transversely nonuniform straight flux tube, anchored in the photosphere, and embedded in a uniform coronal environment. We consider that the magnetic field is twisted and control the strength of magnetic twist by a free parameter of the model. We excite the longitudinally fundamental mode of standing torsional Alfvén waves, whose temporal evolution is obtained by means of high-resolution three-dimensional ideal magnetohydrodynamic numerical simulations. We find that phase mixing of torsional Alfvén waves creates velocity shear in the direction perpendicular to the magnetic field lines. The velocity shear eventually triggers the Kelvin-Helmholtz instability (KHi). In weakly twisted magnetic tubes, the KHi is able to grow nonlinearly and, subsequently, turbulence is driven in the coronal loop in a similar manner as in the untwisted case. Provided that magnetic twist remains weak, the effect of magnetic twist is to delay the onset of the KHi and to slow down the development of turbulence. In contrast, magnetic tension can suppress the nonlinear growth of the KHi when magnetic twist is strong enough, even if the KHi has locally been excited by the phase-mixing shear. Thus, turbulence is not generated in strongly twisted loops
