Simultaneous Inversion For Mantle Conductivity And Source Field: Towards A 3-D Global Reference Model

将开展一项研究计划，以重建地幔电导率的三维可变性。首先，一组最近发布的全球分布的‘响应函数’将被转换成一个全球范围的地幔模型，其细节将比以前可能的更详细。此后，将分析地磁观测站的时间序列数据，目的是设计新的方法，以提取地幔传导性的更高分辨率的视图，特别是在地球外部磁场由昼夜(和谐波)Sq(太阳安静)磁层和电离层电流系统主导的频率上。这有望为未来的上地幔调查提供一个提高空间分辨率的框架，并改善我们对与板块构造关系最密切的区域地球动力学的看法。地幔的电导率取决于温度、组成(如铁含量)、状态(如部分熔体分数)和挥发物的存在。地幔的传导性主要是随着深度的增加而径向增加，但越来越多的证据表明，上地幔和中地幔存在显著的横向非均质性。提出了一项研究计划，该计划将在成像这些三维变化以及解释和理解全球尺度横向电导率变化的地球动力学意义方面取得重大进展。地球电离层和磁层中的外部电流系统(“源电流”)由太阳风活动的变化产生，进而在地球内部引起电流流动。这是一种信号源，可以以电磁‘响应函数’的形式提取，而电磁‘响应函数’又包含有关地球内部导电分布的信息。地磁观测数据的经验正交函数分析简化了解释源电流形态的任务，并提高了所产生的响应函数的质量，这些响应函数被反演以获得更高分辨率的地幔电性模型。对地球内部三维结构和物理状态的新限制，对于致力于了解地球动力学和演化的广大研究人员来说非常重要。联合配准的电学和地震模型可以用来分离三维断层图像中的温度和成分效应，并建立与地球深部物质相关的状态方程。全球3-d电导率参考模型可用于提供边界条件以及大尺度环境，用于对来自区域电磁研究的数据进行建模和反演，例如由美国国家科学基金会大陆动力学计划、边际计划和地球镜(http://www.earthscope.org/links_pubs/index.html).支持的研究全球三维参考模型可供学术、政府和行业团体使用，以解决在诱发的内部磁性变化是噪声源的情况下，例如在利用卫星数据研究地壳磁化或长基线航磁数据时，对数据的污染和有偏见的解释问题。从地球固定参照系来看，磁层和电离层源场的改进特征将非常有助于研究人员使用卫星数据，例如，为主场或地壳场的建模以及电离层和磁层物理研究提供改进的外场校正。改进源场的特征对于卫星感应研究的进展是至关重要的。

A research program will be carried out to reconstruct the three dimensional variability of the electrical conductivity of the mantle. First, a set of recently published globally-distributed 'response functions' will be transformed into a global-scale mantle model with greater detail than previously possible. Following this, geomagnetic observatory time series data will be analyzed with the goal of devising new methods to extract an even higher resolution view of mantle conductivity, particularly at frequencies where the Earth's external magnetic field is dominated by the diurnal (and harmonic) Sq (solar-quiet) magnetospheric and ionospheric electrical current systems. This promises to provide a framework to improve the spatial resolving power for future upper mantle investigations, and to improve our view of the geodynamics of the region most closely associated with plate tectonics.Scientific and technical merit. The electrical conductivity of the mantle depends on temperature, composition (e.g. Fe content), state (e.g. partial melt fraction), and the presence of volatiles. Mantle conductivity primarily increases radially with depth, but a growing body of evidence indicates there is significant lateral heterogeneity in the upper and mid-mantle. A research program is proposed that will lead to significant improvements in imaging these 3-d variations, and in interpreting and understanding the geodynamic significance of global scale lateral conductivity variations. External electrical current systems in the Earth's ionosphere and magnetosphere ("source currents"), generated by variations in solar wind activity, in turn induce electrical current to flow in the Earth's interior. This is a source of signal that may be extracted in the form of electromagnetic 'response functions', which in turn contain information about the distribution of electrical conduction within the Earth's interior. Empirical orthogonal function analysis of geomagnetic observatory data simplifies the task of interpreting the configuration of the source currents, and improves the quality of the resulting response functions, which are inverted to obtain a higher resolution model of the mantle's electrical properties.Broader impacts. New constraints on the 3-d structure and physical state of the Earth's deep interior are of great importance to the broad community of researchers working to understand the dynamics and evolution of the Earth. Co-registered electrical and seismic models can be used to separate temperature and compositional effects in 3-d tomographic images, and to develop equations of state relevant to deep Earth materials. A global 3-d conductivity reference model can be used to provide boundary conditions, as well as large scale context, for modeling and inversion of data from regional electromagnetic studies, such as those supported by the NSF Continental Dynamics Program, the Margins Program, and Earthscope (http://www.earthscope.org/links_pubs/index.html). A global 3-d reference model can be used by academic, government and industry groups to address the problem of contamination and biased interpretation of data in situations where the induced internal magnetic variations are a source of noise, e.g., in studies of crustal magnetization with satellite data, or long-baseline aeromagnetic data. The improved characterization of magnetospheric and ionospheric source fields, as viewed from an Earth fixed reference frame will be very useful to researchers working with satellite data, e.g., to provide improved external field corrections for modeling of the main or crustal fields, and for studies of ionospheric and magnetospheric physics. Improved characterization of source fields is essential to progress in satellite-based induction studies.