Solar and Magnetospheric Plasma Theory

圣安德鲁斯大学的太阳和磁层理论小组将研究太阳大气层和行星磁层中发生的基本物理过程。1.太阳黑子为什么会形成？为什么太阳的外层大气（日冕）比太阳可见表面热100倍以上？在如此高的温度下，太阳气体被电离（等离子体）。3.为什么太阳大气层中会有波动，这些波动能告诉我们太阳大气层中的局部条件是什么？（4）太阳的磁场是如何多年演变的，它是如何与地球相互作用的？5.在太阳磁场扰动期间，电子是如何被加速的？（六）极光的成因是什么？（vii）磁场如何改变其连接？这些关键问题中的许多问题需要多样化的知识基础，SMTG处于回答这些问题的绝佳位置。我们使用数学建模（基础理论，分析模型，计算机模拟，正向建模和观测的组合）研究各种各样的物理现象。这是一种需要的综合办法，即混合使用各种建模方法，并将几个卫星飞行任务的观测结果与理论模型进行比较。我们将使用等离子体理论研究的主题是：i）新的磁场从太阳内部出现，穿过太阳表面进入太阳大气，ii）使用磁流体动力学（MHD）波动理论来推导太阳大气和磁场的性质（日冕地震学），iii）太阳大气层全球磁场的演变iv）使日冕保持比太阳大气层下部更热的物理机制（日冕加热），v）太阳耀斑和日冕物质抛射，这是太阳磁活动的最有力表现，直接影响地球，vi）地球磁层中超低频波的物理学，以及它们如何有助于电子加速导致极光和vii）磁重联，这是一个释放太阳磁化等离子体中储存的巨大能量的极其重要的过程。这些现象遵循可以表示为非线性偏微分方程的物理定律。然而，使它们不同的是，不同的现象需要不同的主导术语。因此，在每种情况下，物理过程和等离子体响应将是不同的。例如，磁重联需要电阻，但MHD波一般不需要。重力在磁通浮现和日珥形成中很重要，但对于磁场重联则不然。太阳耀斑和磁层中的粒子加速需要动力学（粒子）描述，而其他许多研究领域则不需要。非线性方程的复杂性使得它们很难求解，也很难确定每个事件的关键物理过程。一个最重要的研究工具是将许多商用处理器连接在一起而形成的并行计算机。然后，模拟涉及将问题分解为同时（并行）在不同处理器上运行的较小部分。因此，我们的模拟完成得更快。因此，使用256个处理器，在一台机器上需要10年的工作在几周内完成。我们解决STFC科学路线图中的关键问题，特别是太阳如何影响地球？然而，详细了解我们研究课题的物理学不仅对太阳、类太阳恒星和空间天气很重要，而且对了解诸如巨型分子云中星星的形成、恒星周围、黑洞和活动星系核中天体物理盘的演变以及从恒星到河外尺度的风和外流的物理学等各种天体物理过程也很重要。

The Solar and Magnetospheric Theory Group (SMTG) of the University of St Andrews will work on the fundamental physical processes occurring in the Sun's atmosphere and planetary magnetospheres. For example: i) Why do sunspots form? ii) Why is the Sun's outer atmosphere (the corona) over 100 times hotter than the visible surface of the Sun? At such high temperatures, the solar gas is ionized (a plasma). iii) Why are there waves in the Sun's atmosphere and what can these waves tell us about the local conditions there? iv) How does the Sun's magnetic field evolve over many years and how does it interact with the Earth? v) How are electrons accelerated during solar magnetic disturbances? vi) What causes aurora? vii) How does a magnetic field change its connections? Many of these key questions require a diverse knowledge base and the SMTG is in an excellent position to answer these questions. We study a wide variety of physical phenomena using mathematical modelling (a combination of fundamental theory, analytical models, computer simulations, forward modelling and observations). It is an integrated approach that is needed, i.e. a mixture of modelling methods and a comparison between observations from several satellite missions and the theoretical models. The topics we will investigate, using plasma theory, are: i) the emergence of new magnetic field from the solar interior, through the solar surface and into the solar atmosphere, ii) the use of Magnetohydrodynamics (MHD) wave theory to deduce properties of the solar atmosphere and magnetic field (coronal seismology), iii) the evolution of the global magnetic field of the solar atmosphere iv) the physical mechanisms responsible for keeping the corona much hotter than the lower parts of the solar atmosphere (coronal heating), v) solar flares and coronal mass ejections, which are the most powerful manifestations of solar magnetic activity and directly affect the Earth, vi) the physics of ultra-low frequency waves in the Earth's magnetosphere and how they contribute to the acceleration of electrons causing the aurora and vii) magnetic reconnection, a process of extreme importance for releasing the immense amount of energy stored in the Sun's magnetised plasma. These phenomena obey physical laws that can be expressed as non-linear partial differential equations. However, what makes them distinct is that different phenomena require different dominant terms. Hence, the physical processes and the plasma response will be different in each case. For example, magnetic reconnection requires electrical resistance but MHD waves in general do not. Gravity is important in flux emergence and prominence formation, but for magnetic reconnection it is not. Particle acceleration in solar flares and the magnetosphere requires a kinetic (particle) description, while many of the others research areas do not. It is the rich complexity of the non-linear equations that makes them hard to solve and to determine what the key physical processes are responsible for each event. A most important research tool is the parallel computer formed by linking many commodity processors together. Then the simulation involves splitting the problem up into smaller parts that run on different processors at the same time (in parallel). Thus, our simulations are completed quicker. Hence, with 256 processors a job requiring 10 years on single machine, is completed in a couple of weeks. We address key issues in the STFC Science Roadmap, especially, how does the Sun affect the Earth? However, a detailed understanding of the physics of our research topics are important not only for the Sun, solar-like stars and space weather, but also for understanding such diverse astrophysical processes such as star formation in giant molecular clouds, the evolution of astrophysical discs around stars, black holes and in Active Galactic Nuclei, and the physics of winds and outflows from stellar to extragalactic scales.