NSFGEO-NERC: On the origin of extreme variations in Earth's magnetic field

NSFGEO-NERC：地球磁场极端变化的起源

• 批准号: NE/V009052/1
• 负责人: Christopher Davies
• 金额: $ 30.87万
• 依托单位: University of Leeds
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2020
• 资助国家: 英国
• 起止时间: 2020 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FV009052%2F1
• 关键词: NSFGEO; NERC; origin; extreme; variations

Earth's magnetic field has existed for at least 3.5 billion years and exhibits a complex spectrum of spatial and temporal variations on timescales ranging from less than seconds to millions of years. On average the field is thought to adopt a dipole-dominated configuration, which helps protect the surface environment and low-orbiting satellites from the depredations of the solar wind. Significant variations, e.g., the recent growth of a region of anomalously weak field in the southern Atlantic, and excursions and polarity reversals, may alter the shielding effect provided by the field. These surface observations document a dynamo process operating in the liquid core and provide unique insight into the dynamics and evolution of Earth's deep interior. However, data alone cannot constrain the interactions between magnetic field and flow that occur within the core: that requires an internal view of the dynamo. Understanding past field variations and making predictions about future behaviour therefore requires an intimate link between observations and simulations of the generation process. The standard picture of geomagnetic secular variation (SV) is provided by time-dependent global models of the historical, Holocene and longer term field. However, paleomagnetic data also provide evidence for Unusually Rapid Geomagnetic Events (URGEs) in the form of rapid geomagnetic intensity spikes, and directional rates of change that greatly exceed values in these models. While these URGEs are not visible in current global field models, we have recently shown that they are comparable to the fastest changes (called extremal events) produced in numerical dynamo simulations and are compatible with the physics of the dynamo process. Our results also reveal that extremal intensity and directional changes arise in different times and places and are associated with migration of distinct magnetic features at the top of the core. These findings link observations and simulations in a new and more complex view of SV, and suggest new approaches for understanding the dynamo process and our ability to predict its future variations.Progress requires moving beyond simple definitions of extremal events to investigate the spectrum of dynamical behaviour that underpins URGEs. Critical to this goal is using complementary information drawn from paleomagnetic global field models and geodynamo simulations. We propose to develop a new series of global time-dependent geomagnetic field models that can capture rapid changes. In parallel we will produce a new suite of geodynamo simulations accessing the rapidly rotating and vigorously convecting regime thought to describe the dynamics of Earth's core. Synthesis across these approaches will address the following questions: 1. What are the defining spatial and temporal characteristics of URGEs? Do they occur in preferred locations or on systematic timescales? 2. What are the physical origin(s) of URGEs? 3. Are URGEs related to excursions and reversals? 4. Are URGEs related to interactions between the core and mantle and/or stratification at the top of the core?

地球的磁场至少存在35亿年，并且在不到秒至数百万年的时间尺度上表现出复杂的空间和时间变化。平均而言，该领域被认为采用了偶极子主导的配置，这有助于保护表面环境和低孔卫星免受太阳风的偏移。例如，南部大西洋地区异常弱场区域的最新差异以及偏移和极性逆转可能会改变田间提供的屏蔽效应。这些表面观察结果记录了在液体中运行的发电机过程，并为地球深内部的动力学和演变提供了独特的见解。但是，仅数据不能限制核心内发生的磁场和流量之间的相互作用：需要发电机的内部视图。因此，了解过去的现场变化并对未来行为做出预测，需要在观测和生成过程的模拟之间建立紧密的联系。地磁世俗变异（SV）的标准图片由历史，全新世和长期领域的时间依赖性全球模型提供。然而，古磁数据还提供了以快速地磁强度尖峰的形式出现异常快速的地磁事件（冲动）的证据，而在这些模型中极大的变化速率也大大超过了值。尽管这些冲动在当前的全局现场模型中不可见，但我们最近表明它们与数值元模拟中产生的最快变化（称为极端事件）相媲美，并且与发电机过程的物理学兼容。我们的结果还表明，极端强度和方向变化在不同的时间和地点发生，并且与核心顶部的不同磁特征的迁移有关。这些发现将观测和模拟链接在SV的新型和更复杂的视图中，并提出了理解发电机过程的新方法，以及我们预测其未来变化的能力。Progress需要超越对极端事件的简单定义，以研究基于冲突的动力学行为范围。这个目标至关重要的是使用从古磁性全球田间模型和地球模拟中汲取的补充信息。我们建议开发一系列新的全球时间依赖性地磁场模型，以捕获快速变化。同时，我们将制作一套新的Geodynamo模拟套件，以访问迅速旋转和剧烈的对流方案，以描述地球核心的动力学。这些方法中的合成将解决以下问题：1。冲动的定义空间和时间特征是什么？它们发生在首选位置还是系统的时间表上？ 2。冲动的物理起源是什么？ 3。冲动与短途和逆转有关吗？ 4。是否与核心顶部的核心和地幔之间的相互作用和/或分层之间的相互作用有关？

项目成果

Fast Directional Changes during Geomagnetic Transitions: Global Reversals or Local Fluctuations?

• DOI: 10.3390/geosciences11080318
• 发表时间: 2021-07
• 期刊: Geosciences
• 影响因子: 2.7
• 作者: S. Maffei;P. Livermore;J. Mound;Sam Greenwood;C. Davies

Indicators of mantle control on the geodynamo from observations and simulations

观测和模拟中地幔对地球发电机的控制指标

• DOI: 10.3389/feart.2022.957815
• 发表时间: 2022
• 期刊: Frontiers in Earth Science
• 影响因子: 2.9
• 作者: Korte, Monika;Constable, Catherine G.;Davies, Christopher J.;Panovska, Sanja
• 通讯作者: Panovska, Sanja

Combined dynamical and morphological characterisation of geodynamo simulations

地球发电机模拟的组合动力学和形态表征

• DOI: 10.1016/j.epsl.2022.117752
• 发表时间: 2022
• 期刊: Earth and Planetary Science Letters
• 影响因子: 5.3
• 作者: Nakagawa T