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

该项目由美国国家科学基金会地球科学理事会（NSF/GEO）和英国国家环境研究委员会（UKRI/NERC）通过NSF/GEO-NERC牵头机构协议共同资助。该协议允许美国/英国提交一份联合提案，并由其调查员拥有最大比例预算的机构进行同行评审。在成功地共同确定一项奖励后，每个机构为预算的比例和与自己的调查人员有关的调查人员和工作的组成部分提供资金。地球的内部磁场产生于地球液态的外核深处，为地球上的人类居民提供了许多好处。它可以作为太阳风产生的空间天气的保护罩，阻止潜在的破坏性宇宙射线到达地球表面，长期以来一直是导航的基本辅助设备。了解其当前结构是每个智能手机中内置的数字地图工具的固有组成部分，这凸显了了解导致任何意外变化的原因的重要性。在地质和考古记录中，磁场方向和强度的极端变化都以地磁漂移、极性反转和被称为地磁尖峰的快速强度变化的形式发生过。这些将在本项目下进行研究。这项工作的一个组成部分将是在对磁场的地质记录和其行为的现实计算模拟感兴趣的社区之间建立协同方法。了解这些变化的物理起源将增强我们对地球磁场的基本理解，并使我们能够与对地球深层内部和其他行星感兴趣的相关地球物理团体合作。将开发新的方法来研究地磁场的极端变化，该项目将为本科生，研究生和博士后研究人员提供教育，培训和研究指导，同时与英国利兹大学NERC赞助的研究人员开展进一步的国际合作。这项工作将通过两种协同成分提高对驱动极端事件的理解。一种基于地核表面球面三角形镶嵌（STT）的多尺度模拟方法将提高全球磁场模型的区域分辨率。一套新的地球动力学模型将进入适合地球液体核心的快速旋转状态。这些结果将被结合起来评估极端事件经验特征的潜在物理解释。极端场变化对标准正则球谐表示提出了挑战，这些表示依赖于数据不拟合和空间和时间复杂性的全局度量之间的权衡。STT表示将在数据密度高的区域实现更精细的空间和时间分辨率，在数据密度有限的区域实现更低分辨率，从而实现极端区域场行为的鲁棒成像。一个新的状态图描述了非磁对流的行为，具有类似地球的几何形状，浮力强迫和外边界的热流非均匀性，阐明了模拟所需的参数组合，以实现被认为在液体核心中出现的快速旋转和湍流动力学。发电机理论的最新进展将用于设计模拟，以产生可能发生在地核的强磁力，遵循类似地球的旋转速率和扩散率的独特路径，同时保持快速旋转状态。新的和现有的工具将用于评估这些模拟和新的地磁场模型之间的形态和时间相似性，表征可观测场的强度和方向的极端变化，并将这些与潜在的磁流体动力学过程联系起来。该奖项反映了美国国家科学基金会的法定使命，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。

This is a project that is jointly funded by the National Science Foundation’s Directorate of Geosciences (NSF/GEO) and the National Environment Research Council (UKRI/NERC) of the United Kingdom (UK) via the NSF/GEO-NERC Lead Agency Agreement. This Agreement allows a single joint US/UK proposal to be submitted and peer-reviewed by the Agency whose investigator has the largest proportion of the budget. Upon successful joint determination of an award, each Agency funds the proportion of the budget and the investigators associated with its own ivestigators and component of the work.Earth’s internal magnetic field is generated deep in the planet’s liquid outer core and provides many benefits to its human inhabitants. It serves as a protective shield from the space weather generated by the solar wind, inhibits potentially damaging cosmic rays from reaching the surface, and has long served as a fundamental aid for navigation. Knowledge of its current structure is an intrinsic part of the digital mapping tools embedded in every smartphone, highlighting the importance of understanding what causes any unexpected changes. Extreme changes in both direction and strength of the magnetic field have occurred in the geological and archeological records, in the form of geomagnetic excursions, polarity reversals, and rapid intensity variations known as geomagnetic spikes. These will be studied under this project. An integral aspect of the work will be building synergistic approaches across communities interested in the geological record of the magnetic field and realistic computational simulations of its behavior. Understanding the physical origins of these changes will enhance our basic understanding of Earth’s magnetic field, and enable collaborations with related geophysical communities interested in Earth’s deep interior and other planets. New methodologies will be developed to study extreme changes in the geomagnetic field and this project will enable education, training and research mentoring for undergraduate, graduate, and postdoctoral researchers, while developing further international collaborations with NERC sponsored investigators at Leeds University, UK. This work will improve understanding of what drives extreme events using two synergistic components. A multi-scale modeling approach based on spherical triangle tessellations (STT) on the surface of Earth’s core will improve regional resolution in global magnetic field models. A new suite of geodynamo models will access the rapidly rotating regime appropriate to Earth’s liquid core. The results will be combined to assess potential physical interpretations of empirical signatures of extreme events. Extreme field variations present a challenge to standard regularized spherical harmonic representations which rely on trade-offs between data misfit and global measures of spatial and temporal complexity. The STT representation will allow finer spatial and temporal resolution in regions of high data density and lower resolution with limited data, enabling robust imaging of extreme regional field behavior. A new regime diagram describing the behavior of non-magnetic convection with Earth-like geometry, buoyancy forcing, and heat flow heterogeneity at the outer boundary illuminates the parameter combinations needed for simulations to realize the rapidly rotating and turbulent dynamics that are thought to arise in the liquid core. Recent advances in dynamo theory will be used to devise simulations that produce strong magnetic forces as likely occur in the core, following a distinct path towards Earth-like rotation rates and diffusivities while remaining in the rapidly rotating regime. Both new and existing tools will be used to assess the morphological and temporal similarity between these simulations and new geomagnetic field models, characterize extreme changes in intensity and direction of the observable field, and relate these to the underlying magnetohydrodynamic processes.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.