Effect of field divergence on reflectivity of Alfvén waves at the transition region

场发散对过渡区阿尔文波反射率的影响

• 批准号: 2756673
• 金额: --
• 依托单位: Aberystwyth University
• 依托单位国家: 英国
• 项目类别: Studentship
• 财政年份: 2022
• 资助国家: 英国
• 起止时间: 2022 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=studentship-2756673
• 关键词: Effect; field; divergence; reflectivity; Alfv

One of the longstanding problems in solar physics and astrophysics is the mysterious heating of the atmosphere that maintains temperatures above 1 million degrees K. Over the past 70 years different scenarios have been put forward none of which has yet been confirmed. Alfven waves that were discovered during WW2 represent an interplay between the tension of the magnetic field lines and plasma inertia. They therefore resemble waves on a string instrument.Previous studies of Alfven waves have demonstrated their ability to carry significant amounts of energy from the visible surface of the sun known as the photosphere into the atmosphere. Towards the end of their long distance journey Alfven waves can transfer their energy into heating through different mechanisms. Examples include Alfven waves turbulence, phase mixing, and shock heating through nonlinear coupling to compressional waves. The latter mechanism has been shown to be efficient in 1 dimensional studies. These studies have been able to model the propagation of Alfven waves along 1 dimensional loop like structures from the photosphere into the atmosphere. As the waves reach the upper atmosphere of the sun known as the corona, their amplitudes increase which results in their conversion into compressional slow and fast waves. The compressional waves rapidly steepen and turn into shocks resulting in heating of the atmosphere. The energy of the Alfven waves is thus converted into heating.The main advantage of the 1 dimensional studies is their ability to employ a high resolution numerical grid that gives the opportunity to investigate the detailed process of wave propagation, conversion, and steepening into shocks. The drawback is the lack of realistic physics that includes an artificially rigid magnetic field, a simple prescribed field geometry with field lines that always remain in the vicinity of the symmetry axis of the loop.We propose to investigate the propagation of Alfven waves and their role in heating the solar corona by using a 3 dimensional model that is based on an open source code http://pencil-code.nordita.org/. The model will have the ability to incorporate the important effects of thermal conduction and radiation, magnetic field curvature and expansion, gravity and stratification in the atmosphere. The structure geometry will be determined by the interaction between the internal and external magnetic environments in a fully three dimensional physical model. It will become possible to address the propagation of the Alfven waves and their interactions with the longitudinal as well as the transverse waves. The resulting heating of the atmosphere through the processes of wave coupling will be investigated.Our previous studies have demonstrated that plasma jets and surges replicating solar spicules enhance the process of wave amplification and provide important additional energy to the Alfven waves. We would therefore expect to find a similar contribution in a more complex geometry. We will be able to address the role of spicules in Alfven wave amplification and their indirect contribution to the heating process in a more realistic 3 dimensional model. Recent observations with Hinode/EIS, SST, and other instruments have demonstrated the ubiquity of the Alfven waves in the solar atmosphere.The proposed research project will contribute to our understanding of the physics of the sun. It will clarify the role of Alfven waves in the dynamics and energetics of the solar atmosphere. The work will be carried out under MPI on massively parallel shared memory computers using the national supercomputing research facility of Wales (SCW)

太阳物理学和天体物理学中长期存在的问题之一是大气层的神秘加热，使温度保持在 100 万摄氏度以上。在过去 70 年里，人们提出了不同的设想，但没有一个得到证实。二战期间发现的阿尔文波代表了磁力线张力和等离子体惯性之间的相互作用。因此，它们类似于弦乐器上的波。之前对阿尔文波的研究表明，它们能够将大量能量从太阳的可见表面（称为光球层）携带到大气中。在长途旅行即将结束时，阿尔文波可以通过不同的机制将其能量转化为热量。例子包括阿尔文波湍流、相混合以及通过与压缩波的非线性耦合产生的冲击加热。后一种机制已被证明在一维研究中是有效的。这些研究已经能够模拟阿尔文波沿着一维环状结构从光球层到大气中的传播。当波到达太阳的高层大气（称为日冕）时，它们的振幅增加，导致它们转换成压缩慢波和快波。压缩波迅速陡峭并转变为激波，导致大气加热。因此，阿尔文波的能量转化为热量。一维研究的主要优点是能够采用高分辨率数值网格，从而有机会研究波传播、转换和陡峭化为冲击的详细过程。缺点是缺乏现实物理，包括人工刚性磁场、简单规定的场几何形状，其磁力线始终保持在环路对称轴附近。我们建议研究阿尔文波的传播及其作用使用基于开源代码 http://pencil-code.nordita.org/ 的 3 维模型加热日冕。该模型将能够结合大气中的热传导和辐射、磁场曲率和膨胀、重力和分层的重要影响。结构几何形状将由全三维物理模型中内部和外部磁环境之间的相互作用决定。解决阿尔文波的传播及其与纵波和横波的相互作用将成为可能。我们将研究通过波耦合过程产生的大气加热。我们之前的研究表明，复制太阳针状体的等离子射流和浪涌增强了波放大过程，并为阿尔文波提供了重要的额外能量。因此，我们期望在更复杂的几何形状中找到类似的贡献。我们将能够在更真实的 3 维模型中解决骨针在阿尔文波放大中的作用及其对加热过程的间接贡献。最近使用 Hinode/EIS、SST 和其他仪器进行的观测已经证明了阿尔文波在太阳大气中的普遍性。拟议的研究项目将有助于我们了解太阳的物理学。它将阐明阿尔文波在太阳大气动力学和能量学中的作用。这项工作将在 MPI 下利用威尔士国家超级计算研究设施 (SCW) 在大规模并行共享内存计算机上进行