Numerical simulations of planetary and stellar dynamos

行星和恒星的磁场由行星核心或大气层[1]或恒星对流区中的发电机作用维持。该过程涉及通过导电流体的对流运动产生电流[3]。尽管这些运动在空间上是无序的，但发电机的作用在整个太阳系（以及更远的地方）的大部分时间里都维持着全球一致的磁场。典型地，对于类地行星（例如地球），包括发电机停止运行的（例如火星）和卫星（例如木卫三），富铁流体位于地表下深处的（外）核心区域;对于巨行星，（如木星、土星）导电流体是由高压大气中金属氢的形成而产生的;对于恒星来说，导电的等离子体使发电机动作成为可能。尽管流体性质和位置存在这些差异，但产生的各种磁场具有许多共同的特征，例如偶极场的支配和存在于广泛的长度和时间尺度上的动力学。发电机过程究竟如何运作，以及天体的动力学如何受到影响，是行星和恒星科学中悬而未决的问题。对发电机区域动力学的研究将进一步帮助我们理解这个问题，并提高我们预测行星和恒星磁场未来变化的能力。球形发电机是一个复杂的问题，其中对流驱动流和电磁感应的空间和时间动力学必须在称为磁流体力学的物理学分支中一起研究。由于无法直接探测发电机运行的区域，因此进展受阻[2]。因此，我们必须建立流动和磁场的模型，并通过将其输出与自然发生的磁场观测数据进行比较来测试它们。这个博士项目的目的是：1）设计新的和建立在现有的行星和恒星内部流体和磁场的分析和数值模型; 2）在代表性参数制度下进行数值计算和全面模拟; 3）研究模拟数据，进行诊断，并与分析理论和观测数据进行比较。Bullard和H.盖尔曼均匀发电机与地磁。腓Trans. R.Soc. A，247（928）：213-278，1954。[2]D. Gubbins和J. Bloxham。地磁场分析第三部分.核幔边界的磁场地球物理学家。J. R.天文学会，80：695-713，1985. [3]H.K.莫法特导电流体中的场产生。1978.

The magnetic fields of planets and stars are sustained by dynamo action operating in planetary cores or atmospheres [1], or stellar convection zones. The process involves the generation of electric currents via convective motions of the electrically conducting fluid [3]. Despite the motions being spatially disorganised, dynamo action has sustained globally coherent magnetic fields in bodies throughout the Solar System (and beyond) for the majority of its lifetime. Typically, for terrestrial planets (e.g. Earth), including those whose dynamo has ceased to operate (e.g. Mars), and moons (e.g. Ganymede), an iron-rich fluid is located in a (outer) core region deep beneath the surface; for giant planets (e.g. Jupiter, Saturn) the conducting fluid arises by the formation of metallic hydrogen in the high-pressure atmospheres; for stars the electrically conducting plasma enables dynamo action. Despite these differences in fluid properties and location, the various magnetic fields produced have many common characteristics such as domination of dipolar field and dynamics existing on a wide range of length- and time-scales. How the dynamo process exactly operates and how the dynamics of the celestial bodies are affected are outstanding questions in planetary and stellar sciences. Research into the dynamics of dynamo regions will further aid our understanding of this problem and better our ability to predict future changes in planetary and stellar magnetic fields. Spherical dynamos are complicated problems where the spatial and temporal dynamics of convectively driven flows and electromagnetic induction must be studied together in a branch of physicsknown as magnetohydrodynamics. Progress is impeded because it is not possible to directly probe the region where dynamos operate [2]. We must therefore build models of the flow and magnetic field and test them by comparing their outputs with data from observations of naturally-occurring magnetic fields. The aim of the proposed research of this PhD project is to: 1) design new and build on existing analytical and numerical models of fluids and magnetic fields in planetary and stellainteriors; 2) perform numerical calculations and full simulations in representative parameter regimes; 3) study simulation data, perform diagnostics, and compare with analytical theory and observational data.References [1] E. Bullard and H. Gellman. Homogeneous dynamos and terrestrial magnetism. Phil. Trans. R.Soc. A, 247(928):213-278, 1954. [2] D. Gubbins and J. Bloxham. Geomagnetic field analysis. part iii. magnetic fields on the coremantle boundary. Geophys. J. R. Astr. Soc., 80:695-713, 1985. [3] H.K. Moffatt. Field Generation in Electrically Conducting Fluids. 1978.