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?

地球磁场已经存在了至少 35 亿年，并且在时间尺度上表现出复杂的空间和时间变化谱，范围从不到几秒到数百万年。平均而言，该场被认为采用偶极子为主的配置，这有助于保护表面环境和低轨道卫星免受太阳风的掠夺。显着的变化，例如南大西洋异常弱场区域的最近增长以及偏移和极性反转，可能会改变场提供的屏蔽效应。这些表面观测记录了液体核心中运行的发电机过程，并为地球深层内部的动力学和演化提供了独特的见解。然而，仅靠数据无法限制核心内发生的磁场和流动之间的相互作用：这需要发电机的内部视图。因此，了解过去的场变化并对未来的行为进行预测需要在生成过程的观察和模拟之间建立密切的联系。地磁长期变化（SV）的标准图像是由历史、全新世和长期场的时间相关全球模型提供的。然而，古地磁数据还以快速地磁强度峰值和大大超过这些模型中的值的方向变化率的形式提供异常快速地磁事件（URGE）的证据。虽然这些 URGE 在当前的全球场模型中不可见，但我们最近表明，它们与数值发电机模拟中产生的最快变化（称为极值事件）相当，并且与发电机过程的物理原理兼容。我们的结果还表明，极值强度和方向变化出现在不同的时间和地点，并且与地核顶部不同磁性特征的迁移有关。这些发现将观察和模拟以一种新的、更复杂的 SV 观点联系起来，并提出了理解发电机过程和我们预测其未来变化的能力的新方法。进展需要超越极端事件的简单定义，以研究支撑 URGE 的动态行为谱。这一目标的关键是使用从古地磁全球场模型和地球发电机模拟中提取的补充信息。我们建议开发一系列新的全球随时间变化的地磁场模型，可以捕捉快速变化。与此同时，我们将制作一套新的地球发电机模拟，访问快速旋转和剧烈对流的状态，以描述地球核心的动力学。这些方法的综合将解决以下问题： 1. URGE 的定义空间和时间特征是什么？它们发生在首选地点还是按系统时间尺度发生？ 2. URGE 的物理起源是什么？ 3. URGE 与偏离和逆转有关吗？ 4. URGE 是否与地核和地幔之间的相互作用和/或地核顶部的分层有关？

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