Kinematics of coronal rain in a transversely oscillating loop: Ponderomotive force and rain-excited oscillations
Kinematics of coronal rain in a transversely oscillating loop: Ponderomotive force and rain-excited oscillations
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DOI：
10.1051/0004-6361/201629634
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发表时间：
2017-02
影响因子：
6.5
通讯作者：
E. Verwichte;P. Antolin;G. Rowlands;P. Kohutova;T. Neukirch
中科院分区：
文献类型：
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作者：
E. Verwichte;P. Antolin;G. Rowlands;P. Kohutova;T. Neukirch
上下文日冕雨是在太阳日冕环中形成的冷而密集的斑点，是与热不稳定性有关的灾难性冷却的表现。一旦形成，雨福尔斯会以亚弹道的速度落向太阳表面，这一点还没有得到很好的理解。压力似乎是解释这一点的主要候选人。在许多观测中，雨伴随着横向振荡，两者之间的相互作用需要探索。目标。因此，一个替代的运动学模型的日冕雨运动学在横向振荡环的发展，以了解所观察到的亚弹道降落运动的雨的物理性质。它明确地探讨了有质动力所产生的横向振荡对雨运动的作用，以及雨的能力，激发波动。方法.提出了一个分析模型，描述了一个雨滴引导的日冕磁场支持一维剪切阿尔芬波作为一个点质量的振荡字符串。该模型包括重力和有质动力的振荡作用在质量，以及惯性的质量上的振荡。结果雨的运动学在可忽略的雨质量的限制进行了探索，并发现下降和被困制度，取决于波的振幅。在基模的捕获区，雨滴在环顶以与振幅成反比的长周期来回反弹。该模型与几个观测降雨的研究，包括一个深入的比较与观察，显示雨与上下摆动运动。雨惯性的作用，激发横向振荡的倾斜环路进行了探讨。结论.据发现，该模型需要的横向振荡，通常是一个数量级大于观察到的解释所测得的亚弹道运动的雨的位移振幅。因此，可以得出结论，有质动力是不是理解亚弹道运动的主要原因，但它在大回路振荡的情况下发挥作用。雨的出现引起小振幅横向振荡的激发，可以解释观测到的事件，并提供一个地震学工具来测量雨质量。
Context. Coronal rain are cool dense blobs that form in solar coronal loops and are a manifestation of catastrophic cooling linked to thermal instability. Once formed, rain falls towards the solar surface at sub-ballistic speeds, which is not well-understood. Pressure forces seem to be the prime candidate to explain this. In many observations rain is accompanied by transverse oscillations and the interaction between the two needs to be explored. Aims. Therefore, an alternative kinematic model for coronal rain kinematics in transversely oscillating loops is developed to understand the physical nature of the observed sub-ballistic falling motion of rain. It explicitly explores the role of the ponderomotive force arising from the transverse oscillation on the rain motion as well as the capacity of rain to excite wave motion. Methods. An analytical model is presented that describes a rain blob guided by the coronal magnetic field supporting a onedimensional shear Alfven wave as a point mass on an oscillating string. The model includes gravity and the ponderomotive force from the oscillation acting on the mass, as well as the inertia of the mass acting on the oscillation. Results. The kinematics of rain in the limit of negligible rain mass are explored and falling and trapped regimes are found, depending on wave amplitude. In the trapped regime for the fundamental mode, the rain blob bounces back and forth around the loop top at a long period inversely proportional to the oscillation amplitude. The model is compared with several observational rain studies, including one in-depth comparison with an observation that shows rain with up-and down bobbing motion. The role of rain inertia in exciting transverse oscillations is explored in inclined loops. Conclusions. It is found that the model requires displacement amplitudes of the transverse oscillation that are typically an order of magnitude larger than observed to explain the measured sub-ballistic motion of the rain. Therefore, it is concluded that the ponderomotive force is not the primary reason for understanding sub-ballistic motion, but it plays a role in cases of large loop oscillations. The appearance of rain causes the excitation of small-amplitude transverse oscillations that may explain observed events and provide a seismological tool to measure rain mass.