In a previous paper, we computed the energy density and the non-linear energy cascade rate for transverse kink waves using Elsasser variables. In this paper, we focus on the standing kink waves, which are impulsively excited in coronal loops by external perturbations. We present an analytical calculation to compute the damping time due to the non-linear development of the Kelvin-Helmholtz instability. The main result is that the damping time is inversely proportional to the oscillation amplitude. We compare the damping times from our formula with the results of numerical simulations and observations. In both cases we find a reasonably good match. The comparison with the simulations show that the non-linear damping dominates in the high amplitude regime, while the low amplitude regime shows damping by resonant absorption. In the comparison with the observations, we find a power law inversely proportional to the amplitude $η^{-1}$ as an outer envelope for our Monte Carlo data points.
Numerical simulations have revealed a new type of turbulence of unidirectional waves in a plasma that is perpendicularly structured (Magyar et al. 2017), named uniturbulence. For this new type of turbulence, the transverse structuring modifies the upward propagating wave to have both Elsasser variables, leading to the well-known perpendicular cascade. In this paper, we study an analytical description of the non-linear evolution of kink waves in a cylindrical flux tube, which are prone to uniturbulence. We show that they lead to a non-linear cascade for both propagating and standing waves. We c…
The aim of this paper is to point out that the classic seismological problem using observations and theoretical expressions for the periods and damping times of transverse standing magnetohydrodynamic (MHD) waves in coronal loops is better referred to as a reduced seismological problem. Reduced emphasises the fact that only a small number of characteristic quantities of the equilibrium profiles can be determined. Reduced also implies that there is no unique solution to the full seismological problem. Even the reduced seismological problem does not allow a unique solution. Bayesian inference re…
Using full three-dimensional magnetohydrodynamic numerical simulations, we study the effects of magnetic field sigmoidity or helicity on the properties of the fundamental kink oscillation of solar coronal loops. Our model consists of a single denser coronal loop, embedded in a plasma with dipolar force-free magnetic field with a constant alpha-parameter. For the loop with no sigmoidity, we find that the numerically determined oscillation period of the fundamental kink mode matches the theoretical period calculated using WKB theory. In contrast, with increasing sigmoidity of the loop, the actua…
Determining the Polarisation of a Coronal Standing Kink Oscillation Using Spectral Imaging Techniques with the Coronal Multi-channel Polarimeter (CoMP)
Alfvénic Motions in a Stratified Open Flux Tube: Transition from Propagating to Locally Standing Motions and Implications for the Kelvin-Helmholtz Instability
Institute of Frontier and Interdisciplinary Science, Shandong University（山东大学前沿交叉科学研究院）；Shandong Key Laboratory of Space Environment and Exploration Technology, Institute of Space Sciences, Shandong University（山东大学空间科学学院山东省空间环境与探测技术重点实验室）；School of Earth and Space Sciences, Peking University（北京大学地球与空间科学学院）；Centre for mathematical Plasma Astrophysics (CmPA), Department of Mathematics, KU Leuven（荷语鲁汶大学数学系数学等离子体天体物理中心）
Kink oscillations of coronal loops, i.e., standing kink waves, is one of the most studied dynamic phenomena in the solar corona. The oscillations are excited by impulsive energy releases, such as low coronal eruptions. Typical periods of the oscillations are from a few to several minutes, and are found to increase linearly with the increase in the major radius of the oscillating loops. It clearly demonstrates that kink oscillations are natural modes of the loops, and can be described as standing fast magnetoacoustic waves with the wavelength determined by the length of the loop. Kink oscillati…
Context. Kink waves are routinely observed in coronal loops. Resonant absorption is a well-accepted mechanism that extracts energy from kink waves. Nonlinear kink waves are know to be affected by the Kelvin-Helmholtz instability. However, all previous numerical studies consider linearly polarized kink waves. Aims. We study the properties of circularly polarized kink waves on straight plasma cylinders, for both standing and propagating waves, and compare them to the properties of linearly polarized kink waves. Methods. We use the code MPI-AMRVAC to solve the full 3D Magnetohydrodynamic (MHD) eq…
Observational evidence of resonantly damped propagating kink waves in the solar corona
在这封信中，我们建立了明确的证据，共振吸收阻尼机制，通过分析观测数据，从新的日冕多通道偏振仪（CoMP）。该仪器已经确定，在太阳日冕中存在普遍传播的低振幅（$\approx$ 1 km s $^{-1}$）阿尔文波，频率范围很广。从磁流体力学（MHD）波理论实际解释这些波的扭结模式，他们应该表现出一个频率依赖的阻尼长度，由于共振吸收，由TGV关系表明，横向等离子体不均匀性在日冕磁通量管导致他们作为自然的低通滤波器。结果发现，所观察到的频率依赖于阻尼长度（高达约8兆赫）可以解释的扭结波解释，此外，空间平均平衡参数描述的长度尺度的横向等离子体密度不均匀性的系统的日冕环是一致的，从TRACE观测站扭结模式的估计值的范围。
The modulation of the intensity of microwave emission from a plasma slab caused by a standing linear kink fast magnetoacoustic wave is considered. The slab is stretched along a straight magnetic field, and can represent, for example, a current sheet in a flaring active region in corona of the Sun, or a streamer or pseudostreamer stalk. The plasma density is non-uniform in the perpendicular direction and described by a symmetric Epstein profile. The plasma parameter $β$ is taken to be zero, which is a good approximation for solar coronal active regions. The microwave emission is caused by mildl…
Recent observations with the Atmospheric Imaging Assembly (AIA) instrument on the SDO spacecraft have revealed the existence of decayless coronal kink oscillations. These transverse oscillations are not connected to any external phenomena like flares or coronal mass ejections, and show significantly lower amplitudes than the externally excited decaying oscillations. Numerical studies have managed to reproduce such decayless oscillations in the form of footpoint driven standing waves in coronal loops, and to treat them as a possible mechanism for wave heating of the solar corona. Our aim is to …
Aims. We investigate the transfer of energy between a standing kink mode and azimuthal Alfven waves within an expanding flux tube. We consider the process of resonant absorption in a loop with a non-uniform Alfven frequency profile but in the absence of a radial density gradient. Methods. Using the MHD code, Lare3d, we model an oscillating magnetic flux tube that expands radially with height. An initially straight loop structure with a magnetic field enhancement is relaxed towards a force-free state before a standing kink mode is introduced. Results. We demonstrate that the transverse gradient…
Model fitting of kink waves in the solar atmosphere: Gaussian damping and time-dependence
{对太阳大气的观测表明，磁流体动力学波无处不在。测量波浪所用的仪器和技术的改进，现在可以将相互竞争的理论模型的微妙之处与观测到的波浪行为进行比较。一些研究已经开始进行这一进程。然而，用于模型比较的技术通常是不合适的，并且可能导致关于最佳模型的错误结论。这里的目的是介绍一些强大的统计技术模型比较太阳波社区，从天体物理学的其他领域的经验。在这个过程中，我们还旨在研究日冕环振荡的物理学。该方法利用最小二乘拟合将模型与观测数据进行比较。我们证明了模型和观测值之间的残差包含关于模型描述观测值的能力的重要信息，并展示了如何使用各种统计检验来评估它们。特别是，我们讨论了Kolmogorov-Smirnoff一个和两个样本测试，以及运行测试。我们还强调了在模型拟合过程中包括任何观测趋势线的重要性。{To演示的方法，观察一个振荡的冠状环进行站立扭结运动。模型比较技术提供的证据表明，高斯阻尼剖面提供了一个更好的描述所观察到的波衰减比常用的指数剖面。这支持了Pascoe et al.（2016）的先前分析。此外，我们使用的模型比较，以提供证据的时间依赖性波的扭结振荡的性质，归因于当地等离子体的热力学演化的行为。
There has been considerable interest in magnetoacoustic waves in static, straight, field-aligned, one-dimensional equilibria where the exteriors of a magnetic slab are different between the two sides. We focus on trapped, transverse fundamental, oblique quasi-kink modes in pressureless setups where the density varies continuously from a uniform interior (with density $ρ_{\rm i}$) to a uniform exterior on either side (with density $ρ_{\rm L}$ or $ρ_{\rm R}$), assuming $ρ_{\rm L}\leρ_{\rm R}\leρ_{\rm i}$. The continuous structuring and oblique propagation make our study new relative to pertinent…
Kink oscillations of a coronal loop are observed and studied in detail because they provide a unique probe into the structure of coronal loops through MHD seismology and a potential test of coronal heating through the phase-mixing of Alfvén waves. In particular, recent observations show that standing oscillations of loops often involve also higher harmonics, beside the fundamental mode. The damping of these kink oscillations is explained by mode coupling with Alfvén waves. We investigate the consequences for wave-based coronal heating of higher harmonics and what coronal heating observational …
We report our multiwavelength observations of two homologous circular-ribbon flares (CRFs) in active region 11991 on 2014 March 5, focusing on the transverse oscillations of an extreme-ultraviolet (EUV) loop excited by the flares. The transverse oscillations are of fast standing kink-mode. The first-stage oscillation triggered by the C2.8 flare is decayless with lower amplitudes (310$-$510 km). The periods (115$-$118 s) in different wavelengths are nearly the same, indicating coherent oscillations. The magnetic field of the loop is estimated to be 65$-$78 G. The second-stage oscillation trigge…
In recent years, the decay-less regime of standing transverse oscillations in coronal loops has been the topic of many observational and numerical studies, focusing on their physical characteristics, as well as their importance for coronal seismology and wave heating. However, no definitive answer has yet been given on the driving mechanism behind these oscillations, with most studies focusing on the use of periodic footpoint drivers as a means to excite them. In this paper, our goal is to explore the concept of these standing waves being self-sustained oscillations, driven by a constant backg…
Ever since their detection two decades ago, standing kink oscillations in coronal loops have been extensively studied both observationally and theoretically. Almost all driven coronal loop oscillations (e.g., by flares) are observed to damp through time often with Gaussian or exponential profiles. Intriguingly, however, it has been shown theoretically that the amplitudes of some oscillations could be modified from Gaussian or exponential profiles if cooling is present in the coronal loop systems. Indeed, in some cases the oscillation amplitude can even increase through time. In this article, w…
Slow magnetosonic waves associated with flares were observed in coronal loops by SOHO/SUMER, SDO/AIA in various EUV bandpasses, and other instruments. The excitation and damping of slow magnetosonic waves provides information on the magnetic, temperature, and density structure of the loops. Recently, it was found using 1.5D models that the thermal conduction is suppressed and compressive viscosity is enhanced in hot (T>6 MK) flaring coronal loops. We model the excitation and dissipation of slow magnetosonic waves in hot coronal loops with realistic magnetic geometry, enhanced density, and temp…
High-Frequency Magnetohydrodynamic Waves with Substantial Energy in the Solar Polar Corona
Peking University（北京大学）；National Space Science Center, Chinese Academy of Sciences（中国科学院国家空间科学中心）；KU Leuven（荷语鲁汶大学）；Northumbria University（诺森比亚大学）；University of Exeter（埃克塞特大学）；Shandong University（山东大学）
