Three-Dimensional Rotational Dynamics and Coupling of the Core-Mantle System

核幔系统三维旋转动力学与耦合

基本信息

批准号：
NE/G002223/1
负责人：
Jonathan Mound
金额：
$ 30.82万
依托单位：
University of Leeds
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2010
资助国家：
英国
起止时间：
2010 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FG002223%2F1
关键词：
Three Dimensional Rotational Dynamics Coupling

项目摘要

Investigation of the properties and dynamics of the deep interior of the Earth necessarily relies on indirect observations. Seismological studies provide information on the physical properties of the deep Earth and its boundaries and in some cases repeat observations can reveal the dynamics of the deep Earth; for example, the observed 'super-rotation' of the solid inner core. Study of geomagnetic secular variation provides insight on the nature of fluid flow at the surface of the fluid core, and indirect information on the physical properties of the deep Earth. The planet's rotational dynamics provide an additional source of information on the Earth's deep interior and developing a more complete understanding of planetary rotational dynamics is the goal of this project. Variation in the Earth's rotation involves changes in both the rate of rotation (observed as a change in the length of day and correlated with so-called torsional oscillation flow in the fluid core) and the orientation of the rotation axis with respect to the celestial reference frame (periodic fluctuations arising from gravitational interaction with the sun, moon and planets are referred to as nutations). Both length-of-day variations and nutations involve angular momentum exchange between the mantle, outer core and inner core. The strength of the coupling between these regions depends on physical properties of the Earth such as the strength and geometry of the magnetic field within the core, the electrical conductivity of the core and lower mantle, and the viscosities of the outer and inner cores. Although both length-of-day variations and nutations involve similar dynamic effects and provide complementary evidence on the nature of the deep Earth, previous work has tended to analyse these phenomena separately. The first goal of this project is to refine and harmonise the theoretical descriptions of core-mantle coupling in models of nutation and of length-of-day variation. In so doing, we will take advantage of theoretical advances that have occurred to improve one of the types of model, but that have not yet been applied to the other. For example, the theory of viscous coupling in nutation models is more fully developed than that in models of length-of-day. On the other hand, recent work has led to improved descriptions of the geometry of the magnetic field in length-of-day models, and an appreciation for the importance of a commonly neglected effect that adds to ohmic dissipation at the core-mantle boundary. Using the updated models we will reanalyse the existing rotation data sets to obtain improved estimates of the physical properties of the deep Earth. In the final stage of this project we will develop a single model that can self-consistently describe both nutations and torsional oscillations. This would allow for joint inversion of the independent data sets, providing further improvements in the constraints on the physical properties of the deep Earth. The joint model will be used to investigate the dynamics of cross-coupling within the system, including the possibility that torsional oscillations excite an observed decadal-period variation in the orientation of the rotation axis known as the Markowitz Wobble, and a proposed correlation between the timing of phase jumps in the Chandler Wobble (which has a period of 433 days) and so-called geomagnetic jerks (which have also been linked to torsional oscillations). The new information that we gain concerning the physical properties and short time scale dynamics of the Earth's core-mantle system will be useful for testing numerical models of the geodynamo process that is responsible for generation of the Earth's magnetic field.

对地球深处的性质和动力学的研究必然依赖于间接观测。地震学研究提供了有关地球深部及其边界的物理特性的信息，在某些情况下，重复观测可以揭示地球深部的动态；例如，观察到的固体内核的“超级旋转”。地磁长期变化的研究提供了对流体核心表面流体流动性质的深入了解，以及有关地球深处物理特性的间接信息。行星的旋转动力学提供了有关地球内部深处的额外信息来源，并且对行星旋转动力学有更全面的了解是该项目的目标。地球自转的变化涉及自转速率的变化（观察为一天长度的变化，并与流体核心中所谓的扭转振荡流相关）和旋转轴相对于天体参考的方向的变化框架（由于与太阳、月亮和行星的引力相互作用而产生的周期性波动称为章动）。日长变化和章动都涉及地幔、外核和内核之间的角动量交换。这些区域之间的耦合强度取决于地球的物理特性，例如地核内磁场的强度和几何形状、地核和下地幔的电导率以及外核和内核的粘度。尽管日长变化和章动都涉及类似的动态效应，并为地球深处的性质提供了补充证据，但以前的工作倾向于单独分析这些现象。该项目的首要目标是完善和协调章动和日长变化模型中核心-地幔耦合的理论描述。在此过程中，我们将利用已经发生的理论进展来改进其中一种模型，但尚未应用于另一种模型。例如，章动模型中的粘性耦合理论比日长模型中的粘性耦合理论更加成熟。另一方面，最近的工作改进了日长模型中磁场几何形状的描述，并认识到通常被忽视的增加核幔边界欧姆耗散效应的重要性。使用更新的模型，我们将重新分析现有的旋转数据集，以获得对地球深处物理特性的改进估计。在该项目的最后阶段，我们将开发一个可以自洽地描述章动和扭转振荡的单一模型。这将允许对独立数据集进行联合反演，从而进一步改善对地球深处物理特性的限制。该联合模型将用于研究系统内交叉耦合的动力学，包括扭转振荡激发观察到的旋转轴方向十年周期变化（称为马科维茨摆动）的可能性，以及拟议的之间的相关性。钱德勒摆动（周期为 433 天）和所谓的地磁急动（也与扭转振荡有关）中相位跳跃的定时。我们获得的有关地球核心-地幔系统的物理特性和短时尺度动力学的新信息将有助于测试负责产生地球磁场的地球发电机过程的数值模型。