Earth's Core as a Layered System

确定地球磁场的起源对于理解行星的可居住性和演化至关重要，并且被广泛认为是地球科学的基本目标。数十亿年来，该领域一直保护地表环境免受太阳辐射的影响，现在有助于减轻空间天气事件，这些事件可能会通过破坏电信和电网而产生重大的人为影响。然而，产生磁场的发电机过程发生在地表下2800公里的液态金属海洋--铁核中。发电机与上覆地幔的条件密切相关，因此实地观察，结合地震数据和物理模型，提供了对地球从行星形成到现在的深层内部动力学和演变的独特见解。在标准的发电机模型中，整个核心经历湍流运动，并混合成均匀的成分。然而，地磁和地震证据表明，这种模型缺乏基本的物理学，需要重新考虑。最引人注目的磁场变化，偏移和极性反转，最近被41 kyrs前最后一次偏移的第一个全球表示和过去500万年的大量数据所阐明。然而，我的团队的工作表明，基于标准模型的大型发电机模拟套件未能产生与这些新数据集的主要特征相匹配的反向行为。标准模型也无法解释异常的地震结构-在核心顶部100-400 km的E '层和在核心下部100-300 km的F层-它们被解释为稳定分层而不是湍流运动。这些层的存在具有深远的影响，因为F-层介导的功率输入到散装核心产生的领域，而E '-层过滤的信号，我们观察到在地球的表面。我建议，地震和地磁观测可以解释通过查看核心作为一个系统的耦合层，每个有自己独特的动态。为了验证这一假设，我将开发耦合动力学的地球核心（CODEC）的框架，其中包括第一个模型的两相和双扩散流在旋转的磁条件下有关地球的核心和他们的耦合到湍流体。现有的工作还没有研究F层流体动力学，只考虑了简单的表示E '层，所以我将首先进行详细的分析，在这些地区的过程。然后，我将使用编解码器来阐明支撑F层和E '层的地震观测的动力学，这些层的磁性特征，以及在迄今未探索的物理条件下的场生成过程。最后，我将利用CODEC对过去500万年以来的主要磁场变化进行首次重建，从现今的快速动态到极性反转，并研究CODEC预测未来磁场变化的能力。要实现这些目标，就需要对现有的计算机代码进行重大改进，并首次求解新的复杂方程组。无法保证CODEC会产生与观测结果相匹配的磁性特征：其原理是，通过引入正确的物理学，所需的行为将自然出现，类似于单层发电机中自然出现的反转。CODEC只能通过结合流体动力学，材料和计算科学的前沿研究来实现，并将在这些领域中的每一个领域产生新的成果。这项工作将为地球系统中的基本未知因素提供新的约束：核心组成，内核生长以及核心和地幔之间的热量和质量转移。分层似乎是无处不在的地球行星的核心，所以我们的研究结果将提供新的见解，这些机构的动态和演变。

Establishing the origin of Earth's magnetic field is crucial for understanding planetary habitability and evolution and is widely recognised as a fundamental goal in Earth Science. The field has shielded the surface environment from solar radiation for billions of years and now helps mitigate against space weather events, which can have significant anthropogenic impacts by disrupting telecommunications and power grids. Yet the dynamo process that generates the field occurs in the iron core, an ocean of liquid metal 2800 km below the surface. The dynamo is intimately linked to conditions in the overlying mantle and so field observations, combined with seismic data and physical models, provide unique insight into the dynamics and evolution of Earth's deep interior from the formation of the planet to the present day. In the standard dynamo model the whole core undergoes turbulent motion and is mixed to uniform composition. However, geomagnetic and seismic evidence shows that this model lacks essential physics and needs to be reconsidered.The most striking magnetic field variations, excursions and polarity reversals, have recently been illuminated in unprecedented detail by the first global representations of the last excursion 41 kyrs ago and vast curation of data spanning the past 5 million years. However, my group's work has shown that a large suite of dynamo simulations based on the standard model fail to produce reversing behaviour that matches the main features of these new datasets. The standard model also fails to explain anomalous seismic structures - the E'-layer in the top 100-400 km and the F-layer in lower 100-300 km of the core - that are interpreted as stably stratified and not in turbulent motion. The presence of these layers has far-reaching consequences since the F-layer mediates the power input to the bulk core where the field is generated, while the E'-layer filters the signals that we observe at Earth's surface.I propose that both seismic and geomagnetic observations can be explained by viewing the core as a system of coupled layers, each with their own unique dynamics. To test this hypothesis I will develop the COupled Dynamics of Earth's Core (CODEC) framework, which comprises the first models of two-phase and double-diffusive flows in the rotating magnetic conditions relevant to Earth's core and their couplings to the turbulent bulk. Existing work has not yet studied F-layer fluid dynamics and has only considered simple representations of the E'-layer so I will first conduct detailed analysis of the processes in these regions. I will then use CODEC to elucidate the dynamics underpinning seismic observations of the F- and E'-layers, the magnetic signature of these layers, and the process of field generation, at hitherto unexplored physical conditions. Finally, I will use CODEC to produce the first reconstruction of the major field variations over the past 5~Myrs, from rapid present-day dynamics to polarity reversals, and investigate the capacity of CODEC for predicting future field variations.Achieving these goals requires major enhancements to existing computer codes and solutions of new and complex systems of equations for the first time. There is no guarantee that CODEC will produce magnetic features that match observations: the rationale is that by incorporating the correct physics the desired behaviour will emerge naturally, similar to how reversals emerged naturally in single-layer dynamos. CODEC can only be realised by combining cutting-edge research in fluid dynamics, materials and computational science and will yield novel results in each of these domains. The work will deliver new constraints on fundamental unknowns in the Earth system: core composition, inner core growth, and transfer of heat and mass between the core and mantle. Layering seems to be ubiquitous in terrestrial planetary cores and so our results will provide new insight into the dynamics and evolution of these bodies.