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

太阳物理和天体物理学中长期存在的问题之一是大气的神秘加热，使气温保持在100万摄氏度以上。在过去的70年里，人们提出了不同的假设，但没有一个得到证实。第二次世界大战期间发现的阿尔芬波代表了磁力线的张力和等离子体惯性之间的相互作用。因此，它们就像弦乐器上的波。以前对阿尔芬波的研究已经证明，它们能够将大量能量从太阳的可见表面，即光球层携带到大气中。阿尔芬波在长途旅行接近尾声时，可以通过不同的机制将能量转化为热量。例子包括阿尔芬波的湍流、位相混合，以及通过非线性耦合到纵波的激波加热。后一种机制在一维研究中被证明是有效的。这些研究已经能够模拟阿尔芬波沿着一维环状结构从光球层进入大气层的传播。当波到达被称为日冕的太阳上层大气时，它们的幅度增加，这导致它们转化为压缩的慢波和快波。压缩波迅速变陡并转变为激波，导致大气升温。阿尔芬波的能量因此被转化为热量。一维研究的主要优点是它们能够使用高分辨率的数值网格，从而有机会研究波的传播、转换和陡化为激波的详细过程。缺点是缺乏真实的物理，包括一个人工的刚性磁场，一个简单的规定的磁场几何形状，其场线始终保持在环路对称轴的附近。我们建议使用基于开放源代码http://pencil-code.nordita.org/.的三维模型来研究阿尔芬波的传播及其在加热日冕中的作用该模型将能够包含热传导和辐射、磁场弯曲和膨胀、重力和大气层化的重要影响。在全三维物理模型中，结构几何将由内部和外部磁环境之间的相互作用来确定。这将有可能解决阿尔芬波的传播及其与纵波和横波的相互作用。我们将研究通过波耦合过程产生的大气加热。我们之前的研究已经证明，复制太阳针状物的等离子体喷流和浪增强了波的放大过程，并为阿尔芬波提供了重要的额外能量。因此，我们希望在更复杂的几何中也能找到类似的贡献。我们将能够在一个更真实的三维模型中讨论针状体在阿尔芬波放大中的作用以及它们对加热过程的间接贡献。最近用Hinode/EIS、SST和其他仪器进行的观测证明了阿尔芬波在太阳大气中的普遍存在。拟议的研究项目将有助于我们理解太阳的物理。它将阐明阿尔芬波在太阳大气的动力学和能量学中的作用。这项工作将在使用威尔士国家超级计算研究设施(Scw)的大规模并行共享内存计算机上的mpi下进行。

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)