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。例如：i）太阳黑子如何形成、演化和衰变？ii）为什么太阳的外层大气（日冕）比太阳可见表面热100倍以上，以至于气体被电离并形成等离子体？iii）是什么导致了太阳大气层中的波动，这些波动能告诉我们什么关于当地的条件？太阳的磁场是如何在几天、几个月和几年内演变的，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？1.太阳磁场是如何相互作用的？这些关键问题的答案取决于一系列的专业知识，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）太阳内部新磁场的出现，活动区域的形成和演化，冷致密磁层的形成和太阳全球磁场的演化，ii）磁场打破其连通性的物理机制，与邻近的场线重新连接，以及粒子如何加速到高速，iii）使用磁流体力学（MHD）波理论来推导太阳大气和磁场的性质（日冕地震学），iv）负责保持日冕比太阳大气的下部热得多的物理机制（日冕加热），v）3种不同的磁层MHD波的耦合以及行星磁层与其电离层耦合的物理学。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，一个在单机上需要10年的工作，在512个处理器上几周就可以完成。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) How do sunspots form, evolve and decay? ii) Why is the Sun's outer atmosphere (the corona) over 100 times hotter than the visible surface of the Sun so that the gas is ionized and forms a plasma? iii) What causes the 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 days, months and years and how does it interact with the Earth? v) How are electrons accelerated during solar magnetic disturbances? vi) How do solar magnetic fields interact with each other?The answers to many of these key questions depend upon a range of expertise 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, the formation and evolution of active regions, the formation of cool dense prominences and the evolution of the global magnetic field of the Sun, ii) the physical mechanisms through which magnetic fields break their connectivity, reconnect with neighbouring fieldlines and how particles are accelerated to high speeds, iii) the use of Magnetohydrodynamics (MHD) wave theory to deduce properties of the solar atmosphere and magnetic field (coronal seismology), iv) the physical mechanisms responsible for keeping the corona much hotter than the lower parts of the solar atmosphere (coronal heating), v) the coupling of the 3 distinct magnetospheric MHD waves and the physics of the coupling of planetary magnetospheres to their ionospheres. 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 a job that would require 10 years on single machine, will be completed in a couple of weeks on 512 processors. 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.