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首页> 外文期刊>The Astrophysical journal >FREQUENCY AND DAMPING RATE OF FAST SAUSAGE WAVES
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FREQUENCY AND DAMPING RATE OF FAST SAUSAGE WAVES

机译:快速香肠波的频率和阻尼

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摘要

We investigate the frequency and damping rate of fast axisymmetric waves that are subject to wave leakage for a one-dimensional magnetic cylindrical structure in the solar corona. We consider the ideal magnetohydrodynamic (MHD) dispersion relation for axisymmetric MHD waves superimposed on a straight magnetic cylinder in the zero β limit, similar to a jet or loop in the solar corona. An analytic study accompanied by numerical calculations has been carried out to model the frequency, damping rate, and phase speed of the sausage wave around the cut-off frequency and in the long wavelength limit. Analytic expressions have been obtained based on equations around the points of interest. They are linear approximations of the dependence of the sausage frequency on the wave number around the cut-off wavelength for both leaky and non-leaky regimes and in the long wavelength limit. Moreover, an expression for the damping rate of the leaky sausage wave has been obtained both around the cut-off frequency and in the long wavelength limit. These analytic results are compared with numerical computations. The expressions show that the complex frequencies are mainly dominated by the density ratio. In addition, it is shown that the damping eventually becomes independent of the wave number in the long wavelength limit. We conclude that the sausage mode damping directly depends on the density ratios of the internal and external media where the damping declines in higher density contrasts. Even in the long wavelength limit, the sausage mode is weakly damped for high-density contrasts. As such, sausage modes could be observed for a significant number of periods in high-density contrast loops or jets.
机译:我们研究了快速轴对称波的频率和阻尼率,该轴对称波在太阳日冕中受到一维磁性圆柱结构的波泄漏影响。我们考虑了轴对称MHD波的理想磁流体动力学(MHD)色散关系,该波对称叠加在零β极限内的直磁圆柱上,类似于太阳日冕中的射流或环流。进行了一项分析研究,并进行了数值计算,以模拟香肠波在截止频率附近和长波长范围内的频率,阻尼率和相速度。已基于关注点周围的方程式获得了解析表达式。对于泄漏和非泄漏状态以及在长波长范围内,它们是香肠频率对截止波长附近波数的线性近似。此外,在截止频率附近和在长波长范围内都获得了泄漏香肠波的阻尼率的表达式。将这些分析结果与数值计算进行比较。表达式表明,复数频率主要由密度比决定。另外,示出了在长波长范围内阻尼最终变得与波数无关。我们得出的结论是,香肠模式阻尼直接取决于内部和外部介质的密度比,其中内部密度和外部介质的阻尼在较高的密度对比下会下降。即使在长波长范围内,香肠模式也会被弱阻尼以实现高密度对比。这样,可以在高密度对比环或喷嘴中观察到很多时间的香肠模式。

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