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

数值和实验地球动力学模型提供了对地球液态铁核动力学的补充见解。这个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变获得重要的见解。实验产生了地球物理上真实的液态金属流动湍流，远远超出了直接数值模拟的空间分辨率。流动和磁场之间高度非线性相互作用的实验观测提供了关于核心重要过程复杂性的独特信息。计算的并行发展已经为未解决的（亚网格尺度）湍流产生了越来越复杂的模型。这些模型已经在数值地球动力学计算中得到了实现和验证，并取得了显著的成功。然而，由于缺乏“已知”的解决方案来测试亚电网尺度模型的预测，将这些模型推向类地条件的努力目前受到阻碍。使用从实验中精心选择的诊断，可以对数值模型进行更实际的测试。这些模型反过来又有助于对实验的解释，这为改进用于构建亚电网尺度模型的假设奠定了基础。这种计算和实验之间的协同作用是通过合作研究计划最有效地实现的。本研究使用的实验包括球形库埃特流和旋转热对流。在任何一种情况下，外部施加的磁场与液态金属流相互作用。实验设置是基于先前的经验，其明确目标是产生对湍流存在敏感的独特的大规模流动。这些大尺度特征的实验观测被用来检验数值模式的预测。球形库埃特流允许流和磁场之间强烈的（和现实的）相互作用。在快速旋转和强磁场条件下，通过测量液态金属外的感应磁场模式，对地球发电机问题中四个关键子网格模型中的三个模型进行了测试。有或没有施加磁场的旋转对流实验被用来测试第四个亚电网尺度模型。对流实验的主要观测结果包括总热流、大尺度速度和温度波动的功率谱。本研究项目的预期结果是一个更现实的地球动力学模型，该模型结合了复杂的湍流参数化和实验结果数据库，以激励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.