NSFGEO-NERC: Deciphering the Dynamics of Geomagnetic Excursions

NSFGEO-NERC：破译地磁偏移的动力学

• 批准号: 2246758
• 负责人: Catherine Constable
• 金额: $ 41.21万
• 依托单位: University of California-San Diego Scripps Inst of Oceanography
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-06-01 至 2026-05-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2246758&HistoricalAwards=false
• 关键词: NSFGEO; NERC; Deciphering; Dynamics; Geomagnetic

Earth’s internal magnetic field is produced by fluid motions in the liquid, and its sustained presence is of great societal importance because, in addition to providing navigational guidance, it effectively shields the surface environment from the solar wind and space weather. The magnetic field varies on a wide range of time scales and the most striking variations occurring on geological time scales are polarity excursions and reversals. These events can lead to significantly weakened the global field strength, have the societal impacts arising from reduced magnetic shielding of the surface environment, and may be central to understanding the processes that generate and sustain the geomagnetic field in the liquid core. Excursions have received relatively little attention compared to reversals despite occurring more frequently and lasting long enough to cause potentially significant societal disruption. Recent observational models spanning the past hundred thousand years are illuminating the evolution of excursional fields in previously inaccessible detail. When combined with advances in numerical simulation of the physical field generation process, this paves the way for a new approach to understand such enigmatic events. An integral aspect of the work will be building models enabling further synergy across the geomagnetic, paleomagnetic, and numerical geodynamo and, by extension, the international Studies of Earth’s Deep Interior and planetary science communities. This is a collaborative proposal between scientists at the University of California San Diego and Leeds University, and is therefore co-funded by the National Science Foundation (NSF) and the United Kingdom’s Natural Environment Research Council (NERC). Several global, spatial, and temporal representations of Earth’s magnetic field cover 0-100 ka or subsections thereof, and document up to 5 geomagnetic excursions with qualitative similarities as well as distinct differences. Formal definition of excursional field perturbations, duration, local asynchroneity, etc., can be made via the Paleosecular Variation Index allowing comparisons with numerical geodynamo simulations. Expanding the time interval to 0-120 ka, we will produce the first high-resolution models with quantified uncertainty for the Post-Blake excursion at ~95 ka and the Hilina Pali excursion at ~20 ka. In parallel, numerical simulations will build on research at Leeds University (UK) that is defining the requirements for “Earth-like” field behavior. The focus of this proposal is to improve understanding of the nature and origin of geomagnetic excursions using these two synergistic interlinked components. We will(1) Use new and existing global and time-dependent observational models of several excursions during the past 120 kyr to characterize field behavior before, during, and after excursions;(2) Analyze the excursion mechanism and predictability in new geodynamo simulations conducted with a dominant force balance that reflects expected behavior in Earth’s liquid outer core;(3) Develop formal criteria for defining excursions and reconcile paleofield behavior with current and emerging views on Earth-like numerical dynamo simulations.A vital aspect of this proposal is exploiting existing synergy between the Scripps Institution of Oceanography (SIO) observational geomagnetic field modelling and paleosecular variation analysis and Leeds simulations of core dynamics. Observational models will contribute to new Earth-like standards for simulations, which will in turn be used to make high-resolution predictions of observable field variations that can be sought in the lower resolution observational data. We expect to enhance understanding of the dynamics of geomagnetic excursions, including their predictability and relation to polarity reversals.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

地球的内部磁场是由液体中的流体运动产生的，它的持续存在具有重大的社会意义，因为除了提供导航外，它还有效地保护表面环境免受太阳风和空间天气的影响。 磁场在很宽的时间尺度上变化，在地质时间尺度上发生的最引人注目的变化是极性偏移和反转。这些事件可能导致全球磁场强度显着减弱，具有因地表环境磁屏蔽减少而产生的社会影响，并且可能是理解在液核中产生和维持地磁场的过程的核心。 与逆转相比，偏离得到的关注相对较少，尽管发生得更频繁，持续时间也足够长，可能会造成重大的社会破坏。最近的观测模型跨越了过去十万年，以以前无法获得的细节阐明了电磁场的演化。当与物理场生成过程的数值模拟的进步相结合时，这为理解这种神秘事件的新方法铺平了道路。工作的一个组成部分将是建立模型，使地磁，古地磁和数值地球发电机之间进一步协同作用，并通过扩展，地球深部内部和行星科学界的国际研究。这是加州圣地亚哥大学和利兹大学的科学家之间的合作提案，因此由国家科学基金会（NSF）和英国自然环境研究理事会（NERC）共同资助。地球磁场的几个全球、空间和时间表示涵盖了0-100 ka或其中的子部分，并记录了多达5个具有定性相似性和明显差异的地磁漂移。电磁场扰动、持续时间、局部扰动等的形式定义，可以通过允许与数值地球发电机模拟进行比较的古长期变化指数。将时间间隔扩大到0-120 ka，我们将产生第一个高分辨率的模型与量化的不确定性后布莱克偏移在~95 ka和Hilina帕利偏移在~20 ka。与此同时，数值模拟将建立在利兹大学（英国）的研究基础上，该研究正在定义“类地球”场行为的要求。 本建议的重点是利用这两个相互关联的协同作用部分，增进对地磁漂移的性质和起源的了解。我们将（1）使用新的和现有的全球和时间相关的观测模型，在过去120 kyr的几次漂移，以表征场的行为之前，期间和之后的偏移;（2）分析偏移机制和可预测性的新的地球发电机模拟进行的主导力量平衡，反映预期的行为在地球的液体外核;（3）制定正式的标准来定义漂移，并将古油气田行为与当前和新兴的类地数值发电机模拟观点相协调。观测地磁场建模和古长期变化分析以及核心动力学的利兹模拟。观测模型将有助于模拟新的类地标准，而这些标准又将用于对可观测到的场变化进行高分辨率预测，而这些场变化可以在较低分辨率的观测数据中找到。我们希望加强对地磁漂移动态的理解，包括其可预测性和与极性反转的关系。该奖项反映了NSF的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。