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.

地球的磁场通过展示高能量颗粒并保持寿命的表面可居住，从而充当“磁性盾牌”。地球磁场存在的证据可以追溯到数十亿年，并且可能跨越了我们星球的整个时代。尽管它永远存在，但长期以来，地球液体外核中流体运动一直保持磁场的方式仍然是一个谜。实际上，尚不清楚核心历史上最戏剧性事件的时机，即内核的巩固。在地球中心，铁富合金的首次固化将释放出大的能量脉冲，这表现为地球表面磁场的快速变化。到目前为止，在岩石磁记录中尚未发现内部核心固化的明确特征。该项目将通过开发一个数字模拟来解决这个难题，该模拟模拟内部核心固化的影响及其持续增长的效果，这种建模工作的影响将远远超出地球的核心：对核心固化的磁性效果的更好理解可以洞悉地球对随着时间的流逝的冷却以及对古代表面环境的冷却以及是否允许磁性的磁场来保护的磁场，以实现comporty的范围。浮力领域在地球核心中的驾驶会议和发电机动作中夫妇一起，并预测自内部核心成核以来的地磁领域如何被掩盖。在地球的核心中，热和复合浮力场在内部核心边界处耦合，在该边界中，热冷却驱动凝固并释放光元素（组成），这些元素（组成）结合在一起以驱动诱导全球磁场的对流流动。以前尚未在发电机的直接数值模拟中探索这种热化学边界耦合，并且会为如何受到内核生长的影响，对地磁场的影响有了新的启示。项目计划是（1）进一步开发现有的发电机代码（瑞利），以包括任意数量的标量浮力场，每个标量浮力领域，每个都具有各个边界条件和扩散性，（2）对两个相互作用和边界耦合浮力场的物理学进行系统的数值投资。该建模将为地球的核心对流以及内部核心的成长如何影响地球历史上的Geodynamo的增长提供宝贵的新见解。该项目将资助Dostoc来制定该代码，在数值上研究热化学功能耦合，并将这些结果应用于Geodynamo的演变中。该项目是由地球科学局与高级Cyber​​infrasture办公室合作的合作而共同资助的。通过使用基金会的智力优点和更广泛影响的评论标准进行评估。