Investigation of the Causes of Geomagnetic Dipole Moment Change

这项研究将数值发电机模型和发电机理论与现代地磁和古代地磁场的测量相结合，以探索地核地磁偶极变化的起源。正在对短期(10-1000年)、中期(1-10万年)和长期(1-10亿年)时间尺度上的偶极矩变化分别进行研究。PI正在与研究生合作，描绘和解释观测到的核-地幔边界上的短期地磁场变化，这些变化是导致现今地磁偶极矩迅速减小、偶极子倾角更快减小的原因，以及这些持续的磁场变化与流体外核总体环流的关系。特别关注核幔边界上具有反向磁场的区域的生长和运动，包括目前在北大西洋和北美东海岸下方发展的一些反向磁场区域，它们在减少今天的偶极矩和偶极倾斜方面发挥了重要作用。这些磁结构为当今发电机波动的原因提供了实时证据，也为地磁极性反转是如何启动的提供了当代证据。PI正在使用数值发电机模型来研究在古地磁记录中普遍存在的1-10万年的中等时间尺度偶极矩振荡的原因。这项研究检验了这些古地磁偶极子振荡起源的相互竞争的理论，包括波动、流动抖动和进动理论。正在利用高分辨率的发电机数值模型研究极长时间尺度(1-10亿年)上的地磁场变化与地核能量平衡之间的联系，以推导时间平均偶极矩与发电机能源之间的标度关系。然后将这些标度关系外推到地球深部的极端条件，将地磁偶极矩在地质时间尺度上的缓慢变化与控制核心演化的基本物理和化学过程联系起来，这些过程包括固体核心的形成和增长、成因放射性同位素衰变产生的内部加热以及地幔羽流从核心带走热量。

This research combines numerical dynamo models and dynamo theory with measurements of the present-day geomagnetic and the ancient paleomagnetic fields to investigate the origins of geomagnetic dipole change in Earth's core. Separate studies of dipole moment variations over short (10-1000 year), intermediate (1-100 thousand year), and long (1-1000 million year) time-scales are being conducted. In collaboration with graduate students, the PI is delineating and interpreting the observed short-term geomagnetic field changes on the core-mantle boundary that are responsible for the present-day rapid decrease of the geomagnetic dipole moment, the even more rapid decrease of the dipole tilt angle, and the relationship between these on-going magnetic field changes and the general circulation in the fluid outer core. Special attention is given to the growth and movement of regions on the core-mantle boundary with reversed magnetic field, including some reversed field regions now developing beneath the North Atlantic and the east coast of North America, which are playing major roles in reducing the present-day dipole moment and the dipole tilt. These magnetic structures provide real-time evidence on the causes of present-day dynamo fluctuations, as well as contemporary evidence on how geomagnetic polarity reversals are initiated. The PI is using numerical dynamo models to investigate the causes of the 1-100 thousand year, intermediate time-scale dipole moment oscillations that are ubiquitous in the paleomagnetic record. This research tests the competing theories for the origin of these paleomagnetic dipole oscillations, including wave, flow vacillation, and precession theories. The connection between geomagnetic field changes on very long time-scales (1-1000 million years) and the energy balance of the Earth's core is being investigated using high-resolution numerical dynamo models to derive scaling relationships between the time-average dipole moment and dynamo energy sources. These scaling relationships are then extrapolated to the extreme conditions of Earth's deep interior to connect the slow change of the geomagnetic dipole moment over geological time-scales to fundamental physical and chemical processes that control the evolution of the core, including the formation and growth of the solid inner core, internal heating by decay of radiogenic isotopes, and the removal of heat from the core by mantle plumes.