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.

至少在过去的35亿年里，地球一直拥有磁场，这一事实对我们星球的进化有着深远的影响。地磁场保护地表环境和许多轨道卫星免受可能有害的太阳辐射;很久以前，这种屏蔽效应促进了可呼吸大气层的形成。磁场强度远非恒定不变，会随时间和地点的不同而变化;事实上，在过去的150年里，磁场强度一直在下降，导致我们的保护罩减弱。在更大的区域范围内，可以形成弱场补丁，例如目前位于南大西洋的低气压，已知这会导致通过它的卫星出现异常甚至故障，并且还与全球地磁场强度下降和当地气候变化有关。一些预测表明，这片弱场将在未来100年内增长，鉴于社会对卫星和电子基础设施的日益依赖，这可能会产生重大后果。阐明全球和区域磁场变化的过程是预测未来行为的基础。地球磁场的来源位于外核，这是一个位于地球表面以下约2800公里的熔融铁区域。磁力线，就像意大利面条一样，从外核发出，穿过整个地球，穿过表面进入大气层。这个磁场是由铁水的剧烈运动产生的，它扭曲和拉伸磁场线，这一过程需要大量的能量来维持。可用能量的大小决定了铁水的行为（就像水在加热锅中的行为取决于炉子的温度），这反过来又决定了磁场的强度和结构。在一个重要的发展中，我最近的工作表明，可用于驱动铁水运动并因此产生磁场的能量目前比以前认为的小2-3倍。这一结果意味着，地球核心中熔融铁的行为可能与目前的预测非常不同（想象一下，在将炉子温度从沸腾降低到沸腾后，水会发生什么反应），并且目前对导致我们的磁场在空间中变化和时间变化的过程的解释可能是不正确的。在更基本的层面上，我们目前还不知道我们的地球是如何在其历史的大部分时间里支持磁场的，因为现在的能量减少给解释过去35亿年磁场存在的所有先前模型带来了重大问题。地球外核可用能量的急剧减少促使我们对地磁场的理解发生了过去20年来最大的变化之一。要重新建立一个解释磁场长期存在的基本理论，需要一个模型来描述外核如何随着时间的推移而演变，从而达到今天的状态。我最近开发了一个新的外核演化数学模型，它解决了以前模型遇到的技术困难。在接下来的五年里，我将利用这个模型来了解地球在过去35亿年中是如何支持其磁场的，从而为我们星球上最遥远和神秘的地区提供基本的新视野。我将利用这些信息对地球的外核进行计算机模拟，这将建立负责产生我们观察到的复杂磁场行为的过程，并对该领域的未来行为进行预测，包括全球磁场强度的演变和弱磁场的补丁。

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

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

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

Penetration of boundary-driven flows into a rotating spherical thermally stratified fluid

边界驱动流渗透到旋转球形热分层流体中

• DOI: 10.1017/jfm.2018.999
• 发表时间: 2019
• 期刊: Journal of Fluid Mechanics
• 影响因子: 3.7
• 作者: Cox G