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

地球的磁场通过偏转高能粒子并保持表面适合生命居住而起到“磁屏蔽”的作用。 地球磁场存在的证据可以追溯到数十亿年前，可能跨越我们星球的整个年龄。 尽管磁场一直存在，但它是如何通过地球液态外核中的流体运动维持的，这仍然是一个谜。 事实上，在地核历史上最戏剧性的事件--内核的凝固--发生的时间并不清楚。 地球中心富铁合金的第一次凝固预计将释放出巨大的能量脉冲，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迹象。 该项目将通过开发一种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推移在表面磁场上的持续增长的影响。 这项建模工作的影响将远远超出地球核心：更好地了解地核凝固的磁效应可以深入了解地球如何随着时间的推移而冷却，以及古代地表环境是否受到允许生命蓬勃发展的磁屏蔽的保护。该项目的目标是在社区发电机代码中实施额外的浮力场，研究热浮力场和成分浮力场如何耦合在一起，驱动地球核心的对流和发电机作用，并预测自内核成核以来地磁场的表现。在地核中，热浮力场和成分浮力场在内核边界处耦合，在内核边界处，热冷却驱动固化并释放轻元素（成分），轻元素（成分）联合收割机结合在一起以驱动对流流动，从而引起全球磁场。这种热化学边界耦合以前没有在发电机的直接数值模拟中进行过探索，这将为地磁场如何受到内核生长的影响提供新的线索。该项目计划是（1）执行现有发电机代码（瑞利）的进一步发展，包括任意数量的标量浮力场，每个单独的边界条件和扩散率，和（2）进行系统的数值研究的物理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行动。该模型将提供有价值的新的见解如何地球的核心对流和如何内核的增长影响了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行动，并将这些结果应用于地球发电机的发展。该项目由地球科学理事会和高级网络基础设施办公室共同资助，以支持人工智能/地球科学中的ML和开放科学活动。该奖项反映了NSF的法定使命，并通过使用基金会的学术价值和更广泛的影响评审标准。

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.