Collaborative Research: CSEDI--Integrating Numerical and Experimental Geodynamo Models

数值和实验地球发电机模型提供了对地球液态铁核动力学的补充见解。这一研究项目的目标是利用这两种方法的优势，对地球磁场的起源和演化获得重要的见解。这些实验在液态金属流动中产生了地球物理上真实的湍流，远远超出了直接数值模拟的空间分辨率。对流动和磁场之间高度非线性相互作用的实验观察提供了关于核心中重要过程的复杂性的独特信息。计算的并行进步已经产生了越来越复杂的未分辨(次网格尺度)湍流模型。这些模型已经在数值地质发电机计算中得到了实施和检验，取得了显著的成功。然而，目前，将这些模型推向类似地球的条件的努力受到了阻碍，因为缺乏“已知的”解决方案来测试次网格规模的模型的预测。使用从实验中精心选择的诊断方法，可以对数值模型进行更现实的测试。这些模型反过来又有助于对实验的解释，这为完善构建次网格规模模型所用的假设奠定了基础。这种计算和实验之间的协同是最有效地通过合作研究计划实现的。本研究中使用的实验包括球面Couette流动和旋转热对流。在任何一种情况下，外部施加的磁场都会与液态金属流动相互作用。这些实验装置基于先前的经验，明确的目标是产生对湍流的存在敏感的独特的大尺度流动。对这些大尺度特征的实验观测被用来检验数值模式的预测。球面Couette流允许流动和磁场之间的强烈(和现实的)相互作用。在地球发电机问题中的四个关键亚网格尺度模型中，有三个模型正在快速旋转和强磁场条件下通过测量液态金属外部的感应磁场模式进行测试。旋转对流实验，在有和没有外加磁场的情况下，正在被用来测试第四个亚网格尺度的模型。对流实验中的主要观测包括总热流、大尺度速度和温度波动的功率谱。这一研究项目的预期结果是一个更现实的地球发电机模型，它包含了复杂的湍流参数和一个实验结果数据库，以刺激其他研究小组使用不同的建模策略进行类似的比较。

Numerical and experimental geodynamo models offer complementary insights into the dynamics of the Earth's liquid iron core. The goal of this research project is to leverage the strengths of both approaches to gain significant insights into the origin and evolution of the Earth's magnetic field. The experiments produce geophysically realistic turbulence in liquid metal flows that are well beyond the spatial resolution of direct numerical simulations. Experimental observations of highly nonlinear interactions between the flow and the magnetic field provide unique information about the complexity of important processes in the core. Parallel advances in computation have produced increasingly sophisticated models for unresolved (subgrid-scale) turbulence. These models have been implemented and tested in numerical geodynamo calculations with remarkable success. However, the effort to push these models to Earth-like conditions is presently hampered by the lack of "known" solutions to test the predictions of the subgrid-scale models. Use of carefully chosen diagnostics from the experiments enables more realistic tests of the numerical models. The models, in turn, aid the interpretation of the experiments, which establishes a foundation for refining the assumptions used in the construction of the subgrid-scale models. This synergy between computations and experiments is most effectively realized through a collaborative research program.The experiments used in this study include spherical Couette flow and rotating thermal convection. In either case, an externally imposed magnetic field interacts with the liquid metal flow. The experimental setups are based on prior experience with the explicit goal of producing distinctive large-scale flows that are sensitive to the presence of turbulence. Experimental observations of these large-scale features are used to test the predictions of the numerical models. Spherical Couette flow permits strong (and realistic) interactions between the flow and the magnetic field. Three of the four key subgrid-scale models in the geodynamo problem are being tested under the conditions of rapid rotation and strong magnetic fields by measuring the pattern of induced magnetic field outside the liquid metal. Rotating convection experiments, with and without an imposed magnetic field, are being used to test the fourth subgrid-scale model. The primary observations in the convection experiments include the total heat flow, the large-scale velocity and the power spectra of temperature fluctuations. The expected outcome of this research project is a more realistic geodynamo model that incorporates sophisticated parameterizations for turbulence and a database of experimental results to stimulate other research groups to engage in similar comparisons using different modeling strategies.