Probing the Earth's subdecadal core-mantle dynamics based on satellite geomagnetic field models

基于卫星地磁场模型探测地球亚年代际核幔动力学

• 批准号: 225387973
• 负责人: Dr. Seiki Asari
• 金额: --
• 依托单位: Institut für Mathematik
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2012
• 资助国家: 德国
• 起止时间: 2011-12-31 至 2014-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/225387973?language=en
• 关键词: Probing; Earth; subdecadal; core; mantle

The CHAMP mission provided a great amount of geomagnetic data all over the globe from 2000 to 2010. Its dense data coverage has allowed us to build GRIMM | GFZ Reference Internal Magnetic Model | which has the highest ever resolution for the core field in both space and time. We have already modeled the fluid flow in the Earth's outer core by applying the diffusionless magnetic induction equation to the latest version of GRIMM, to find that the flow evolves on subdecadal timescales, with a remarkable correlation to the observed fluctuation of Earth rotation. These flow models corroborated the presence of six-year torsional oscillations in the outer core fluid. Torsional oscillation (TO) is a type of hydromagnetic wave, theoretically considered to form the most important element of decadal or subdecadal core dynamics. It consists of relative azimuthal rotations of rigid fluid annuli coaxial with the mantle's rotation and dynamically coupled with the mantle and inner core. In preceding works, the TOs have been studied by numerical simulations, either with full numerical dynamos, or solving eigenvalue problems ideally representing the TO system. While these studies drew insights about dynamical aspects of the modeled TOs, they did not directly take into account the observations of geomagnetic field and Earth rotation. Particularly, there have been no observation-based studies for the TO using satellite magnetic data or models. In the proposed project, we aim at revealing the subdecadal dynamics and energetics of the Earth's core-mantle system on the basis of satellite magnetic observations. To that end, we will carry out four work packages (1) to (4), for all of which we use GRIMM. (1) We perform time-series analyses of core field and flow models, to carefully extract the signals from TOs at different latitudes. (2) We refine the conventional flow modeling scheme by parameterizing the magnetic diffusion at the core surface. Here, the diffusion term is reinstated in the magnetic induction equation, which is dynamically constrained by relating it to the Lorentz term in the Navier-stokes equation. (3) We develop a method to compute the electromagnetic core-mantle coupling torque on the core fluid annuli, whereby the energy dissipation due to the Joule heating is evaluated for each annulus. This analysis would provide insights on whether the Earth's TOs are free or forced oscillations. (4) Bringing together physical implications and computational tools obtained by (1) to (3), we finally construct a dynamical model for the Earth's TOs and core-mantle coupling such that they are consistent with GRIMM and Earth rotation observation. This modeling is unique in that the force balances concerning the TOs are investigated in time domain, as well as that the modeling also aims at improving the observation-based core flow model by considering the core dynamics.

从2000年到2010年，冠军任务在全球范围内提供了大量的地磁数据。其密集的数据覆盖范围使我们能够构建Grimm | GFZ参考内部磁模型|在时空和时间上，这是有史以来核心场的最高分辨率。我们已经通过将无扩散的无磁感应方程式应用于最新版本的Grimm来建模地球外部芯中的流体流量，以发现该流量在子量的时间尺度上演变，与观察到的地球旋转波动的相关性显着相关。这些流模型证实了外核流体中六年扭转振荡的存在。扭转振荡（TO）是一种水力磁波，从理论上讲，它们构成了年代或子核心核心动力学中最重要的元素。它由刚性流体Annuli同轴的相对方位角旋转与地幔的旋转组成，并与地幔和内核动态耦合。在上述作品中，TOS通过数值模拟（具有完整数值发电机）或解决特征值问题的数值模拟进行了研究。尽管这些研究吸引了有关模型TOS动力学方面的见解，但它们并未直接考虑到地磁场和地球旋转的观察结果。特别是，没有针对使用卫星磁数据或模型的基于观察的研究。在拟议的项目中，我们旨在根据卫星磁性观测来揭示地球核心系统系统的亚次数动力学和能量。为此，我们将对所有使用Grimm进行四个工作包（1）至（4）。 （1）我们对核心场和流模型进行时间序列分析，以仔细地从不同纬度的TO中提取信号。 （2）我们通过在芯表面参数化磁扩散来完善常规流动建模方案。在这里，扩散项在磁感应方程中恢复了，该方程将通过将其与Navier-Stokes方程中的Lorentz项相关联。 （3）我们开发了一种计算核心流体环上电磁核棒耦合扭矩的方法，从而评估每个环的焦耳加热引起的能量耗散。该分析将提供有关地球TO是自由还是强制振荡的见解。 （4）将（1）至（3）获得的物理含义和计算工具汇总在一起，我们最终为地球的TOS和核心掩体耦合构建了动力学模型，使它们与Grimm和Earth Rotation观察一致。这种建模是独一无二的，因为在时域中研究了有关TOS的力平衡，并且该建模还旨在通过考虑核心动力学来改善基于观测的核心流模型。