Dynamics of the earth's fluid and solid cores

这项研究的目的是提高我们对地球流体核心的动力学及其与内核和地幔的相互作用的了解。尽管描述这些系统的物理学很复杂，但通过关注动力学的特定方面可以取得进展。这项研究的一般方法是通过调查地球磁场、自转和重力场的预测变化是否与这些量的实际观测相一致来测试简单的动力学模型。被研究的地核的具体动力学方面包括扭转振荡，在磁数据中检测到的具有圆柱形几何形状的核心流动，以及地球的自转变化。问题在于，这些振荡是自由模式，就像由弹簧悬挂的质量，还是由基本动力学造成的强迫运动。我将通过数值模拟来研究这种流动的性质。另一个项目是调查所谓的“地磁突变”的原因，“地磁突变”是指大约一年的时间尺度上发生的磁力变化。我建议研究流动与地核表面附近磁场之间的作用，并测试哪种情况与观测结果最相符。使用相同的框架，我还将研究所谓的“考古磁性突变”的原因，这种突变是在几千年的更长时间尺度上观察到的。在同一时间尺度内，将对考古磁性观测进行调查，以确定在过去几个世纪中观测到的CMB赤道附近磁场特征的运动是否在过去更长时间内是地球发电机的特征。最后，有两个项目涉及内核在地球自转动力学中的作用。首先，观测到的地球自转速度以6年为周期的变化被解释为内核和地幔之间的轴向振荡。将对重力场和磁场数据进行调查，以寻找这种振荡的进一步证据。在第二个项目中，我将研究内核附近的流动和磁场的动力学，通过它们在内核上施加扭矩的能力，导致其图形倾斜，并导致地球自转方向的变化。

The goal of this research is to improve our knowledge of the dynamics in the Earth's fluid core and its interaction with the inner core and mantle. Though the physics describing these systems is complex, progress can be made by focusing on specific aspects of the dynamics. The general approach in this research is to test simple models of the dynamics by investigating whether the predicted variations in the Earth's magnetic field, rotation and gravity field are compatible with actual observations of these quantities. Specific dynamical aspects of the Earth's core that are studied include torsional oscillations, a core flow with a cylindrical geometry detected in the magnetic data and the Earth's rotation variations. Questions remain as to whether these oscillations are free modes, like a mass suspended by a spring, or forced motions by the underlying dynamics. I will study the nature of this flow by numerical modelling. Another project is to investigate the cause of the so-called "geomagnetic jerks", which are magnetic variations occurring on a timescale of approximately 1 year. I propose to study the action between flows and magnetic field near the surface of the core and to test which scenario is most compatible with observations. Using the same framework, I will also study the cause of the so-called "archaeomagnetic jerks", which are observed over a much longer timescale of millennia. Over the same timescale, archaeomagnetic observations will be surveyed to determine whether the motions of magnetic field features near the equator of the CMB observed over the past few centuries have been a feature of the geodynamo for much longer in the past. Finally, two projects involve the role of the inner core in the rotational dynamics of the Earth. First, observed variations in the Earth's rotation rate with a period of 6 years are interpreted to represent axial oscillations between the inner core and mantle. Gravity field and magnetic field data will be surveyed to find further evidences of this oscillation. In the second project, I will study the dynamics of the flow and magnetic field near the inner core, through their ability to imprint a torque on the latter which leads to a tilt of its figure and causes a change in the direction of Earth's rotation.