Numerical simulations of planetary and stellar dynamos

行星和恒星的磁场是由行星核心、大气层或恒星对流带中的发电机作用维持的。这个过程包括通过导电流体[3]的对流运动产生电流。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。通常，对于类地行星（例如地球），包括那些发电机已经停止运转的行星（例如火星）和卫星（例如木卫三），富含铁的流体位于地表以下深处的（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；对恒星来说，导电等离子体能产生发电机作用。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特征，例如偶极磁场的主导作用以及存在于广泛的长度和时间尺度上的动力学。发电机过程究竟是如何运作的，天体的动力学是如何受到影响的，这些都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，其中对流驱动流动和电磁感应的时空动力学必须在称为磁流体力学的物理学分支中一起研究。进展受到阻碍，因为不可能直接探测发电机运行的区域。因此，我们必须建立流体和磁场的模型，并通过将它们的输出与自然产生的磁场的观测数据进行比较来测试它们。本博士项目拟进行的研究目的是：1)在现有的行星和星际室内流体和磁场分析和数值模型的基础上，设计新的模型；2)在具有代表性的参数范围内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。参考文献b[1] E.布拉德和H.格尔曼。均质发电机和地磁。菲尔。反式。R.Soc。中国生物医学工程学报，2009(4):344 - 344。[qh] D.格宾斯和J.布洛克斯汉姆。地磁场分析。第三部分。地核边界上的磁场。地球物理学。阿斯特。Soc。中文信息学报，80:695-713,1985。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.