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Decayless Kink Oscillations Excited by Random Driving: Motion in Transitional Layer
Solar Physics ( IF 2.8 ) Pub Date : 2021-08-18 , DOI: 10.1007/s11207-021-01867-5
M. S. Ruderman 1, 2, 3 , N. S. Petrukhin 4 , E. Pelinovsky 5, 6, 7
Affiliation  

In this article we study the plasma motion in the transitional layer of a coronal loop randomly driven at one of its footpoints in the thin-tube and thin-boundary-layer (TTTB) approximation. We introduce the average of the square of a random function with respect to time. This average can be considered as the square of the oscillation amplitude of this quantity. Then we calculate the oscillation amplitudes of the radial and azimuthal plasma displacement as well as the perturbation of the magnetic pressure. We find that the amplitudes of the plasma radial displacement and the magnetic-pressure perturbation do not change across the transitional layer. The amplitude of the plasma radial displacement is of the same order as the driver amplitude. The amplitude of the magnetic-pressure perturbation is of the order of the driver amplitude times the ratio of the loop radius to the loop length squared. The amplitude of the plasma azimuthal displacement is of the order of the driver amplitude times \(\text{Re}^{1/6}\), where Re is the Reynolds number. It has a peak at the position in the transitional layer where the local Alfvén frequency coincides with the fundamental frequency of the loop kink oscillation. The ratio of the amplitude near this position and far from it is of the order of \(\ell\), where \(\ell\) is the ratio of thickness of the transitional layer to the loop radius. We calculate the dependence of the plasma azimuthal displacement on the radial distance in the transitional layer in a particular case where the density profile in this layer is linear.



中文翻译:

随机驱动激发的无衰减扭结振荡:过渡层中的运动

在本文中,我们研究了在细管和薄边界层 (TTTB) 近似中随机驱动的日冕环过渡层中的等离子体运动。我们介绍了随机函数关于时间的平方的平均值。这个平均值可以被认为是这个量的振荡幅度的平方。然后我们计算径向和方位角等离子体位移的振幅以及磁压力的扰动。我们发现等离子体径向位移和磁压扰动的幅度在过渡层上没有变化。等离子体径向位移的幅度与驱动器幅度具有相同的数量级。磁压扰动的幅度是驱动器幅度乘以环路半径与环路长度平方之比的数量级。等离子体方位角位移的幅度是驱动器幅度倍的数量级\(\text{Re}^{1/6}\),其中 Re 是雷诺数。它在过渡层中局部阿尔芬频率与环路扭结振荡的基频重合的位置处具有峰值。该位置附近和远离该位置的幅度之比为\(\ell\)量级,其中\(\ell\)是过渡层的厚度与环半径的比值。我们计算了在过渡层中密度分布是线性的特定情况下等离子体方位位移对过渡层中径向距离的依赖性。

更新日期:2021-08-19
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