Numerical Modeling of Thermo-chemical Convection in Earths Core and Implications for Geodynamo Evolution

地核热化学对流的数值模拟及其对地球发电机演化的影响

• 批准号: 2200322
• 负责人: Peter Driscoll
• 金额: $ 38.92万
• 依托单位: Carnegie Institution of Washington
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2022
• 资助国家: 美国
• 起止时间: 2022-08-01 至 2024-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2200322&HistoricalAwards=false
• 关键词: Numerical; Modeling; Thermo; chemical; Convection

Earth’s magnetic field acts as a “magnetic shield” by deflecting high energy particles and keeping the surface habitable for life. Evidence for the existence of Earth’s magnetic field goes back billions of years, and may span the entire age of our planet. Despite its ever-presence, the way the magnetic field has been maintained by fluid motion in Earth’s liquid outer core for so long remains a mystery. In fact, the timing of the most dramatic event in the core’s history, the solidification of the inner core, is not known. The first solidification of the iron-rich alloy at the center of the Earth is expected to release a large pulse of energy that is manifested as a rapid change in the magnetic field at Earth’s surface. So far no clear signature of inner core solidification has been found in the rock magnetic record. This project will address this conundrum by developing a numerical simulation that models the effects of inner core solidification and its continued growth over time on the surface magnetic field. The impact of this modeling effort will go well beyond Earth’s core: a better understanding of the magnetic effects of core solidification can provide insight into how Earth has cooled over time and whether the ancient surface environment was protected by a magnetic shield that allowed life to flourish.The goal of this project is to implement additional buoyancy fields in a community dynamo code, investigate how thermal and compositional buoyancy fields couple together in driving convection and dynamo action in Earth’s core, and predict how the geomagnetic field has behaved since inner core nucleation. In Earth’s core the thermal and compositional buoyancy fields are coupled at the inner core boundary where thermal cooling drives solidification and releases light elements (composition) that combine together to drive convective flows that induce a global magnetic field. This thermo- chemical boundary coupling has not previously been explored in direct numerical simulations of the dynamo, and will shed new light on how the geomagnetic field was influenced by the growth of the inner core. The project plan is to (1) perform further development of an existing dynamo code (Rayleigh) to include an arbitrary number of scalar buoyancy fields, each with individual boundary conditions and diffusivities, and (2) perform a systematic numerical investigation of the physics of two interacting and boundary-coupled buoyancy fields undergoing rotating convection and dynamo action. The modeling will provide valuable new insight into how Earth’s core convects and how the growth of the inner core has influenced the geodynamo over Earth history. The project will fund a postdoc to develop the code, numerically investigate coupled thermo-chemical dynamo action, and apply these results to the evolution of the geodynamo.This project is co-funded by a collaboration between the Directorate for Geosciences and Office of Advanced Cyberinfrastructure to support AI/ML and open science activities in the geosciences.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.

地球磁场起到了“磁屏蔽”的作用，使高能粒子偏转，使地球表面适合生命居住。地球磁场存在的证据可以追溯到数十亿年前，并且可能跨越我们地球的整个时代。尽管它一直存在，但磁场是如何在地球液态外核的流体运动中维持这么长时间的，仍然是一个谜。事实上，地核历史上最具戏剧性的事件，即内核的凝固，发生的时间是未知的。富铁合金在地球中心的第一次凝固预计会释放出一个巨大的能量脉冲，表现为地球表面磁场的快速变化。到目前为止，在岩石磁记录中还没有发现内核凝固的明显特征。该项目将通过开发一个数值模拟来解决这个难题，该模拟模拟了内核凝固及其随时间对表面磁场的持续增长的影响。这项建模工作的影响将远远超出地核：更好地了解地核凝固的磁效应可以帮助我们深入了解地球是如何随着时间的推移而冷却的，以及古代的地表环境是否受到磁屏蔽的保护，从而使生命得以繁衍。该项目的目标是在社区发电机代码中实现额外的浮力场，研究热浮力场和组成浮力场如何耦合在一起驱动地核中的对流和发电机作用，并预测自内核成核以来地磁场的行为。在地核中，热和成分浮力场在内核边界处耦合，在那里热冷却驱动凝固并释放轻元素（成分），这些轻元素结合在一起驱动对流，从而诱发全球磁场。这种热化学边界耦合以前还没有在发电机的直接数值模拟中进行过探索，它将为地磁场如何受到内核生长的影响提供新的线索。项目计划是：(1)对现有的发电机代码（Rayleigh）进行进一步的开发，以包括任意数量的标量浮力场，每个浮力场都具有单独的边界条件和扩散率；(2)对两个相互作用和边界耦合的浮力场进行旋转对流和发电机作用的物理系统数值研究。该模型将提供有价值的新见解，以了解地核如何对流，以及内核的增长如何影响地球历史上的地球发电机。该项目将资助博士后开发代码，数值研究耦合热化学发电机作用，并将这些结果应用于地球发电机的演变。该项目由地球科学理事会和先进网络基础设施办公室共同资助，以支持地球科学领域的人工智能/机器学习和开放科学活动。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。