Solar and Magnetospheric Plasma Theory

圣安德鲁斯大学的太阳和磁层理论小组（SMTG）将研究太阳大气和行星磁层中发生的基本物理过程。例如：i)太阳黑子为什么会形成？ii)为什么太阳的外层大气（日冕）比太阳可见表面的温度高100多倍？在这样的高温下，太阳气体被电离（等离子体）。为什么太阳大气中会有波，这些波能告诉我们那里的当地情况？iv)多年来太阳的磁场是如何演变的，它是如何与地球相互作用的？v)在太阳磁场扰动期间，电子如何加速？极光的成因是什么？磁场如何改变其连接？这些关键问题中的许多都需要多样化的知识库，而SMTG在回答这些问题方面处于绝佳的位置。我们使用数学建模（基础理论、分析模型、计算机模拟、正演建模和观测的结合）研究各种各样的物理现象。需要的是一种综合办法，即混合使用各种建模方法，并将若干卫星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)从太阳内部，穿过太阳表面，进入太阳大气的新磁场的出现，ii)利用磁流体动力学（MHD）波动理论来推断太阳大气和磁场的性质（日冕地震学），iii)太阳大气全球磁场的演变，iv)使日冕比太阳大气下部热得多的物理机制（日冕加热），v)太阳耀斑和日冕物质抛射，这是太阳磁活动最强大的表现形式，直接影响地球；vi)地球磁层中超低频波的物理学，以及它们如何促进电子加速，导致极光；vii)磁重联，这是一个对释放储存在太阳磁化等离子体中的巨大能量至关重要的过程。这些现象遵循可以用非线性偏微分方程表示的物理定律。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。重力在通量的产生和日珥的形成中是重要的，但在磁重联中则不是。太阳耀斑和磁层中的粒子加速需要动力学（粒子）描述，而许多其他研究领域则不需要。正是非线性方程的丰富复杂性使得它们很难求解，也很难确定导致每个事件的关键物理过程是什么。一个最重要的研究工具是将许多商品处理器连接在一起形成的并行计算机。然后模拟涉及到将问题分解成更小的部分，这些部分同时在不同的处理器上运行（并行）。因此，我们的模拟可以更快地完成。因此，对于256个处理器，在一台机器上需要10年才能完成的工作，在几周内就可以完成。我们解决了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，详细了解我们的研究主题的物理学不仅对太阳，类太阳恒星和空间天气很重要，而且对理解诸如巨大分子云中的恒星形成，恒星周围天体物理盘的演化，黑洞和活动星系核，以及从恒星到星系外尺度的风和流出物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.