Tuning Dynamo Models to Paleomagnetic Observations

在整个地球历史中，地磁场的记录被保存在考古文物中，或者在全球分布的沉积岩和火成岩中。具有相关年龄限制的考古地磁和古地磁数据汇编现在通常用于制作可以从现在延伸到1万年前的地磁场的连续时变模型。提出的工作将把古地磁的这些进展与地球发电机的研究联系起来，以产生更真实的发电机模型，并了解它们如何与地球深部过程联系起来，包括其流体外核动力学和核-地幔相互作用。我们的研究成果将有助于地球深部的跨学科研究，并将通过同行评审文献的出版物和与其他地球深部研究人员的互动广泛传播给其他人，这些研究人员为其他nsf资助的计划做出了贡献，特别是为地球深部研究合作研究所（CIDER）和地球动力学计算基础设施（CIG）。我们习惯于在EarthRef数字档案社区数据库中系统地电子归档工具和产品。这些将对其他研究地磁学/古磁学的研究人员有用，我们还存档的图像、模型和动画将在多个层面上用于一般研究和教育目的，为公众提供有关地磁场的教育工具。该项目还将通过指导和培训斯克里普斯的一名研究生来加强未来的STEM活动和研究。教育和推广工作将来自PI与斯克里普斯桦树水族馆的互动以及正在进行的斯克里普斯国家科学基金会kp -12项目。我们对千禧年地磁模型的评估表明，它们足以研究世界许多地区的大规模地磁场变化。在千年时间尺度上，我们观察到磁通量主要集中在地核-地幔边界的流动性，磁通量在两极上空普遍较低，以及低纬度地区的特征漂移。在百万年的时间尺度上，我们可以绘制出平均磁场和它的统计变异性，我们有偶极矩的时变模型，包括它在极性漂移和反转期间的急剧下降。在发电机模拟方面的平行进展允许常规生产能够自我逆转的主要偶极场，并且在适当的边界条件下，可以模拟近几个世纪以来观察到的空间结构，并在更长的时间尺度上提供令人鼓舞的相关性。这一提议的目的是调整这些模型，使它们能够更好地再现古场变化的推断属性，从而增强我们对核心动力学的理解。这将通过使用一套具有可访问的Ekman， Rayleigh和Prandtl数值的模拟来完成，并参与外核垂直和横向浮力剖面变化的系统探索，这些变化与核心的热演化模型有关。这一机制将有助于研究液体地核顶部强烈稳定的分层层对可观测磁场的影响，并将提供有关赋予地磁场结构和稳定性的热学和化学过程的见解。磁场是携带地球深部信息的少数直接观测物之一：因此，我们期望我们的结果能够影响地球深部结构和核-地幔相互作用的矿物学和地震学模型。

Throughout Earth's history records of the geomagnetic field have been preserved in archeological artifacts, or in globally distributed sedimentary and igneous rocks. Compilations of archeomagnetic and paleomagnetic data with associated age constraints are now routinely used to make continuous time-varying models of the geomagnetic field that can extend from the present to 10 thousand years ago. The work proposed will link these advances in paleomagnetism with those in studies of the geodynamo to produce more realistic dynamo models and understand how they are linked to deep Earth processes including dynamics of its fluid outer core and core-mantle interactions. Results from our research will contribute to inter-disciplinary studies of the deep Earth and will be broadly disseminated to others through publications in peer-reviewed literature and via interactions with other deep-Earth researchers contributing to other NSF-funded initiatives, particularly the CIDER (Cooperative Institute for Deep Earth Research) and CIG (Computational Infrastructure for Geodynamics). We make a habit of systematic electronic archiving of tools and products in the EarthRef Digital Archive community database. These will be of use to other researchers in geo/paleomagnetism, and the images, models, and animations that we also archive will be useful for general research and educational purposes at multiple levels, providing tools for public education about the geomagnetic field. This project will also enhance future STEM activities and research through mentoring and training of a graduate student at Scripps. Education and outreach efforts will result from the PI's interactions with Scripps' Birch Aquarium and the ongoing NSF GK-12 program at Scripps.Our assessment of millennial geomagnetic models suggests that they are adequate to study large-scale geomagnetic field variations in many regions of the world. On thousand year time-scales we observe mobility of the main concentrations of magnetic flux on the core-mantle boundary, generally low flux over the poles, and drift of features at lower latitudes. On million year time-scales we can map the average field and its statistical variability and we have time-varying models of the dipole moment, including its dramatic fall during polarity excursions and reversals. Parallel progress in dynamo simulation allows routine production of predominantly dipolar fields that are capable of self-reversal and, with appropriate boundary conditions, can mimic spatial structures observed over recent centuries and provide encouraging correlations over longer time-scales. The intent of this proposal is to tune such models so that they do a better job of reproducing inferred properties of paleofield variations, thereby enhancing our understanding of core dynamics. This will be accomplished by using a suite of simulations with accessible values of the Ekman, Rayleigh, and Prandtl numbers and engaging in a systematic exploration of changes in both vertical and lateral buoyancy profiles in the outer core that are linked to models of the thermal evolution of the core. This regime will allow investigation of the influence of strongly stably stratified layers at the top of the liquid core on the observable magnetic fields, and will provide insight about the thermal and chemical processes that lend structure and stability to the geomagnetic field. The magnetic field is one of the few direct observables that carry information about the deep Earth: we therefore expect our results to influence mineralogical and seismological models of deep Earth structure and core-mantle interaction.