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arXiv 1703.02423astro-ph.SR
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电阻率和粘性对振荡冕环中Kelvin-Helmholtz不稳定性的影响

The effects of resistivity and viscosity on the Kelvin-Helmholtz instability in oscillating coronal loops

Thomas Howson, Ineke De Moortel, Patrick Antolin

摘要:

目的-调查电阻率和粘度对振荡日冕环中开尔文-亥姆霍兹不稳定性(KHI)的发生和增长的影响。方法-我们模拟了三维(3-D),电阻磁流体动力学代码,Lare 3D的密度增强回路中的扭结驻波。我们进行了参数研究的粘度和电阻率系数,以研究耗散对KHI的影响。结果-提高粘度和电阻率的行为,以抑制KHI。较大的值会延迟不稳定性的形成,在某些情况下,会完全阻止不稳定性的发生。这导致较早的加热开始较小的值的传输系数。我们注意到粘度比电阻率对KHI的发展有更大的影响。此外,当使用异常电阻率时,与KHI相关联的欧姆加热速率可能大于与在不稳定性抑制状态(使用均匀电阻率)中发生的相混合相关联的欧姆加热速率。结论-从我们的研究,很明显,加热速率至关重要地取决于形成小的长度尺度(受数值分辨率的影响)以及电阻率和粘度的值。由于输运系数的较大值抑制KHI,加热的开始被延迟,但加热速率较大。随着数值分辨率的提高,可以形成更小的长度尺度,即使对于相同的输运系数,加热速率也会更高。

英文摘要:

Aims - Investigate the effects of resistivity and viscosity on the onset and growth of the Kelvin-Helmholtz instability (KHI) in an oscillating coronal loop. Methods - We modelled a standing kink wave in a density-enhanced loop with the three dimensional (3-D), resistive magnetohydrodynamics code, Lare3d. We conducted a parameter study on the viscosity and resistivity coefficients to examine the effects of dissipation on the KHI. Results - Enhancing the viscosity and resistivity acts to suppress the KHI. Larger values delay the formation of the instability and, in some cases, prevent the onset completely. This leads to the earlier onset of heating for smaller values of the transport coefficients. We note that viscosity has a greater effect on the development of the KHI than resistivity. Furthermore, when using anomalous resistivity, the Ohmic heating rate associated with the KHI may be greater than that associated with the phase mixing that occurs in an instability-suppressed regime (using uniform resistivity). Conclusions - From our study, it is clear that the heating rate crucially depends on the formation of small length scales (influenced by the numerical resolution) as well as the values of resistivity and viscosity. As larger values of the transport coefficients suppress the KHI, the onset of heating is delayed but the heating rate is larger. As increased numerical resolution allows smaller length scales to develop, the heating rate will be higher even for the same transport coefficients.

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