A New Energy Budget for Earth's Core and Implications for the Geomagnetic Field

地核的新能源预算及其对地磁场的影响

• 批准号: NE/L011328/1
• 负责人: Christopher Davies
• 金额: $ 57.35万
• 依托单位: University of Leeds
• 依托单位国家: 英国
• 项目类别: Fellowship
• 财政年份: 2015
• 资助国家: 英国
• 起止时间: 2015 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FL011328%2F1
• 关键词: New; Energy; Budget; Earth; Core

Earth has possessed a magnetic field for at least the last 3.5 billion years, a fact that has profound implications for the evolution of our planet. The geomagnetic field shields the surface environment and the many orbiting satellites from potentially harmful incoming solar radiation; long ago, this shielding effect facilitated the formation of a breathable atmosphere. The field strength is far from constant, varying from place to place and also in time; indeed, the field strength has been decreasing for the last 150 years, leading to a weakening of our protective shield. On a more regional scale, patches of weak field can develop, such as the current low located in the southern Atlantic, which is known to cause anomalies and even failures in satellites that pass through it and has additionally been linked to the global decrease in geomagnetic field strength and local climate variability. Some predictions suggest that this patch of weak field will grow over the next 100 years, which could have significant consequences given society's increasing reliance on satellites and electronic infrastructure. Elucidating the processes that produce global and regional changes in the magnetic field is fundamental for predicting future behaviour.The source of Earth's magnetic field lies inside the outer core, a region of molten iron some 2800km below Earth's surface. Magnetic field lines, like strands of spaghetti, emanate from the outer core and thread through the whole Earth, passing through the surface and off into the atmosphere. This field is generated by vigorous motion of the molten iron, which twists and stretches the magnetic field lines, a process that requires a significant amount of energy to maintain. The amount of available energy determines the behaviour of the molten iron (just like the behaviour of water in a heated pan depends on the temperature of the stove), which in turn dictates the strength and structure of the magnetic field. In a significant development, my recent work has shown that the energy available to power the molten iron into motion, and hence generate the magnetic field, is presently 2-3 times smaller than previously thought. This result implies that the behaviour of the molten iron in Earth's core may be very different to current predictions (imagine how the water reacts after turning the stove temperature down from boil to simmer), and that current interpretations of the processes causing our magnetic field to vary in space and change in time may be incorrect. At a more fundamental level, we do not currently know how our planet has managed to support a magnetic field for much of its history because the present-day energy reduction causes significant problems for all previous models that explain the existence of the field for the last 3.5 billion years. The dramatic reduction in energy available to Earth's outer core is prompting one of the biggest changes to our understanding of the geomagnetic field in the last 20 years. To reestablish a basic theory that explains the long-term existence of the magnetic field requires a model that describes how the outer core has evolved over time and therefore arrived its present-day state. I have recently developed a new mathematical model of outer core evolution that alleviates the technical difficulties encountered by previous models. Over the next five years I will use this model to understand how the Earth has supported its magnetic field for the last 3.5 billion years, thereby providing fundamental new sight into the most remote and enigmatic region of our planet. I will use this information to make computer simulations of the Earth's outer core, which will establish the processes responsible for producing the complex magnetic field behaviour we observe and make predictions about future behaviour of the field including the evolution of the global field strength and patches of weak magnetic field.

在过去的35亿年中，地球拥有一个磁场，这一事实对我们星球的发展具有深远的影响。地磁场屏蔽了表面环境，许多轨道卫星免受潜在有害的太阳辐射。很久以前，这种屏蔽效果促进了透气氛围的形成。田间强度远非恒定，随着时间的及时而异。实际上，在过去的150年中，野外强度一直在降低，导致我们的保护屏蔽层削弱。在更具区域尺度上，可以发展出弱场的斑块，例如位于南部大西洋的当前低点，众所周知，这会引起异常，甚至在通过它的卫星中发生故障，并且还与地磁田地强度和局部气候变化的全球降低相关。一些预测表明，这一薄弱领域将在未来100年内增长，鉴于社会对卫星和电子基础设施的依赖越来越大，这可能会产生重大的后果。阐明在磁场中产生全球和区域变化的过程对于预测未来的行为至关重要。地球磁场的来源位于外部芯内，外部芯内是地球表面以下约2800公里的熔融铁的区域。磁场线（如意大利面条的链），从外芯散发出来，并穿过整个地球，穿过表面并流入大气中。该场是由熔融铁的剧烈运动产生的，熔融铁扭曲并拉伸磁场线，这一过程需要大量的能量维护。可用能量的量决定了熔融铁的行为（就像加热锅中的水的行为取决于炉子的温度），进而决定了磁场的强度和结构。在一个重大的发展中，我最近的工作表明，为熔融铁推动运动并产生磁场的能量目前比以前想象的要小2-3倍。该结果意味着，熔融铁在地球核心中的行为可能与当前的预测有很大不同（想象一下水在将炉子温度从沸腾下降到沸腾的炉子后如何反应），并且对导致我们的磁场在空间变化和时间变化的过程的当前解释可能是不正确的。从更加基本的角度来看，我们目前不知道我们的星球如何在其大部分历史上为磁场提供支持，因为当今的减少能源会导致所有以前的模型，这些模型解释了过去35亿年内该领域的存在。地球外部核心可用的能源的急剧减少是促使我们对过去20年中对地磁领域的理解的最大变化之一。为了重新建立一个基本理论，解释了磁场的长期存在，需要一个模型，该模型描述了外部芯如何随着时间的流逝而发展，因此到达了当今的状态。我最近开发了一种新的数学模型的外核进化模型，以减轻以前模型遇到的技术困难。在接下来的五年中，我将使用该模型来了解地球在过去的35亿年中如何支持其磁场，从而为我们地球上最遥远，最神秘的地区提供基本的新景象。我将使用此信息对地球外部核心进行计算机模拟，这将建立负责产生我们观察到的复杂磁场行为的过程，并对该场的未来行为做出预测，包括全球磁场强度和弱磁场的斑块的演变。

项目成果

Thermo-Chemical Dynamics in Earth's Core Arising from Interactions with the Mantle

地核与地幔相互作用产生的热化学动力学

• DOI: 10.31223/x5mw4g
• 发表时间: 2021
• 作者: Davies C

Transfer of oxygen to Earth's core from a long-lived magma ocean

• DOI: 10.1016/j.epsl.2020.116208
• 发表时间: 2020-05-15
• 期刊: EARTH AND PLANETARY SCIENCE LETTERS
• 影响因子: 5.3
• 作者: Davies, Christopher J.;Pozzo, Monica;Alfe, Dario
• 通讯作者: Alfe, Dario

Constraints from material properties on the dynamics and evolution of Earth's core

• DOI: 10.1038/ngeo2492
• 发表时间: 2015-09-01
• 期刊: NATURE GEOSCIENCE
• 影响因子: 18.3
• 作者: Davies, Christopher;Pozzo, Monica;Alfe, Dario
• 通讯作者: Alfe, Dario

Partitioning of Oxygen Between Ferropericlase and Earth's Liquid Core

• DOI: 10.1029/2018gl077758
• 发表时间: 2018-06
• 期刊: Geophysical Research Letters
• 影响因子: 5.2
• 作者: Christopher J. Davies;M. Pozzo;David Gubbins;Dario Alfè

Performance of parallel-in-time integration for Rayleigh Bénard convection

瑞利贝纳德对流的时间并行积分性能

• DOI: 10.1007/s00791-020-00332-3
• 发表时间: 2020
• 期刊: Computing and Visualization in Science
• 作者: Clarke A