Inverting Observations of Hydromagnetic Vibrations of the Earth's Core for the Structure and Dynamics of the Core and Boundary Region

人们普遍认为，地球磁场的起源是液态铁核中对流的结果，但对其中的过程却几乎没有达成共识。数值地球动力学模型已经非常成功地再现了地球表面磁场的特征。然而，不同模型的内部工作原理可能有很大的不同。由于缺乏关于地核动态状态的信息，区分这些可能性的努力受到阻碍。研究者建议利用地核中的水磁波（扭转振荡）来恢复地核和边界区域的动力学信息。这些振动对地核表面的流体流动、白天长度的变化和重力场的变化都有可观察到的影响。历史和基于卫星的观测将使用一个新的理论框架进行分析，该框架依赖于常用于正态地震学的方法。基础的数学模型描述了水磁波，以及伴随的地幔和内核的运动。该模型将用于联合反演地核表面的流动观测、日长变化和重力变化，以获得激发波的磁场内部结构和对流过程（类似于地震学中的地球结构和震源机制的参数）。我们对地核结构和动力学的理解的进步将为地球发电机的运行和能量消耗提供新的见解。这些问题对于理解我们自己星球的热化学演化至关重要，也许也是为什么金星和火星的演化如此不同的原因。

EAR-0309531Bruce BuffettThe origin of Earth's magnetic field is broadly understood to be a consequence of convection in the liquid iron core, yet there is little consensus on the processes involved. Numerical geodynamo models have been remarkably successful in reproducing features of Earth's field at the surface. However, the internal workings of different models can be vastly different. Efforts to distinguish between these possibilities are hampered by a lack of information about the dynamical state of Earth's core. The investigator proposes to use hydromagnetic waves (torsional oscillations) in the core to recover information about the dynamics of the core and boundary regions. The vibrations have observable consequences for fluid flow at the surface of the core, variations in the length of day and changes in the gravity field. Historical and satellite-based observations will be analyzed using a new theoretical framework that relies on methods commonly employed in normal-mode seismlogy. The underlying mathematical model describes the hydromagnetic waves, as well as the accompanying motion of the mantle and inner core. This model will be used to jointly invert observations of flow at the core surface, variations in length of day, and changes in gravity for the internal structure of the magnetic field and convective processes that excite the waves (parameters analogous to earth structure and source mechanism in seismology). Progress in our understanding of the structure and dynamics of Earth's core will provide new insights into the operation and power consumption of the geodynamo. These issues are crucial for understanding the thermal and chemical evolution of our own planet, and perhaps why Venus and Mars evolved so differently.