Investigation of the Causes of Geomagnetic Dipole Moment Change

地磁偶极矩变化原因探讨

• 批准号: 0604974
• 负责人: Peter Olson
• 金额: --
• 依托单位: Johns Hopkins University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-07-01 至 2010-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0604974&HistoricalAwards=false
• 关键词: Investigation; Causes; Geomagnetic; Dipole; Moment

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.

本研究将数值发电机模型和发电机理论与现今地磁场和古地磁场的测量相结合，以研究地球核心地磁偶极子变化的起源。在短（10-1000年），中（1- 10万年），长（1- 10亿年）的时间尺度上的偶极矩变化的单独研究正在进行。在与研究生的合作中，PI正在描绘和解释所观察到的核-幔边界上的短期地磁场变化，这些变化是导致当今地磁偶极矩快速下降，偶极子倾角甚至更快下降的原因，以及这些持续的磁场变化与流体外核中的大气环流之间的关系。特别注意的增长和运动的区域的核幔边界上的反向磁场，包括一些反向场区域，现在开发的北大西洋和北美东海岸，这是发挥重要作用，在减少现今的偶极矩和偶极子倾斜。这些磁结构提供了关于当今发电机波动原因的实时证据，以及关于地磁极性逆转如何启动的当代证据。PI正在使用数字发电机模型来调查1- 10万年，中间时间尺度的偶极矩振荡的原因，这些振荡在古地磁记录中无处不在。这项研究测试这些古地磁偶极振荡的起源，包括波，流摆动和岁差理论的竞争理论。正在利用高分辨率数字发电机模型研究地磁场在很长时间尺度（1- 10亿年）上的变化与地核能量平衡之间的联系，以推导出时间平均偶极矩与发电机能源之间的比例关系。这些比例关系，然后外推到地球内部深处的极端条件下连接地磁偶极矩在地质时间尺度的缓慢变化的基本物理和化学过程，控制核心的演变，包括固体内核的形成和增长，内部加热的放射性同位素的衰变，并从核心的地幔柱的热量。