Effect of Variable Background on an Oscillating Hot Coronal Loop
Effect of Variable Background on an Oscillating Hot Coronal Loop
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DOI：
10.1007/s11207-013-0225-8
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发表时间：
2013-04-01
期刊：
影响因子：
2.8
通讯作者：
Erdelyi, R.
中科院分区：
文献类型：
--
作者：
Al-Ghafri, K. S.;Erdelyi, R.
我们调查的效果的变量，即随时间变化，背景上的常设声学（即纵向）模式产生的热日冕循环。应用描述冠状环的1D几何形状的理论模型。背景温度可以作为时间的函数变化，并经历指数衰减，具有典型的日冕环的特征冷却时间。假设磁场是均匀的。热传导被认为是阻尼热日冕振荡的主要机制，在存在一个物理上未指定的热力学源，保持初始平衡。本文分析了背景等离子体快速冷却对声（纵）驻波特性的影响。利用Wenzel-Kramers-Brillouin理论推导了随时间变化的色散关系和振幅。利用Sturm-Liouville问题的性质，得到了描述热传导对驻波纵向（声）波影响的随时间变化的振幅的解析解.接下来，数值评估进一步说明了在具有可变的、随时间变化的背景的系统中的驻声波的行为。结果被应用到一些检测到的环路振荡。我们发现一个显着的理论预测和观测之间的协议。尽管出现的冷却背景等离子体在介质中，热传导被发现造成一个很强的阻尼的慢驻磁声波在热日冕环一般。除此之外，热导率值的增加导致纵向驻波慢MHD波的振幅的强烈衰减。
We investigate the effect of a variable, i.e. time-dependent, background on the standing acoustic (i.e. longitudinal) modes generated in a hot coronal loop. A theoretical model of 1D geometry describing the coronal loop is applied. The background temperature is allowed to change as a function of time and undergoes an exponential decay with characteristic cooling times typical for coronal loops. The magnetic field is assumed to be uniform. Thermal conduction is assumed to be the dominant mechanism for damping hot coronal oscillations in the presence of a physically unspecified thermodynamic source that maintains the initial equilibrium. The influence of the rapidly cooling background plasma on the behaviour of standing acoustic (longitudinal) waves is investigated analytically. The temporally evolving dispersion relation and wave amplitude are derived by using the Wenzel-Kramers-Brillouin theory. An analytic solution for the time-dependent amplitude that describes the influence of thermal conduction on the standing longitudinal (acoustic) wave is obtained by exploiting the properties of Sturm-Liouville problems. Next, numerical evaluations further illustrate the behaviour of the standing acoustic waves in a system with a variable, time-dependent background. The results are applied to a number of detected loop oscillations. We find a remarkable agreement between the theoretical predictions and the observations. Despite the emergence of the cooling background plasma in the medium, thermal conduction is found to cause a strong damping for the slow standing magneto-acoustic waves in hot coronal loops in general. In addition to this, the increase in the value of thermal conductivity leads to a strong decay in the amplitude of the longitudinal standing slow MHD waves.