Advances in Paleomagnetic Field Modeling: How does Earth&#39;s dipole grow and decay?

GSTDTAP

项目编号	1623786
	Advances in Paleomagnetic Field Modeling: How does Earth's dipole grow and decay?
	Catherine Constable
主持机构	University of California-San Diego Scripps Inst of Oceanography
项目开始年	2016
	2016-07-01
项目结束日期	2019-06-30
资助机构	US-NSF
项目类别	Continuing grant
项目经费	114397(USD)
国家	美国
语种	英语
英文摘要	Part 1: Studies of the past magnetic field are important to a broad range of the geosciences. The dipole moment is our primary shield against energetic particles in the solar wind, controlling the production of cosmogenic isotopes in the upper atmosphere. Estimates of past dipole moment are used to infer cosmogenic isotope production and hence contribute to proxies for solar flux in paleoclimate studies. They also help inform us about expected hazard levels associated with space weather. The geomagnetic field exhibits large changes on a range of temporal and spatial scales, but the focus here is on the past 100 ka. Time varying representations of the field derived from paleo and archeomagnetic data reveal an overall geographic asymmetry in field structure for the past 10 ky with stronger average fields in the northern hemisphere and more active secular variation in the southern hemisphere. There is a long-term increase in the dipole from about 6000 BC until 300 AD, and one interval exhibiting particularly strong growth corresponds to the rapid appearance of regional spikes in field strength in the Levantine region. Since 300 AD the axial dipole strength has generally declined from its peak of around 120 ZAm2 to the present day value near 80 ZAm2. The regional extent and impact of the Levantine field spikes has yet to be fully elucidated, and it remains an open question whether similar features occur at other places and times. This proposal has two major goals. The first is to explore the relationship between spike-like behavior, dipole growth, and other field properties. The second is to understand changes that lead to intervals of decreasing dipole moment as is happening today and occurred in more dramatic form during the Laschamp excursion centered about 41 ka. Results will contribute to numerous areas where general or specific knowledge is needed about the geomagnetic field and its variability on centennial to million year time scales. Systematic electronic archiving of tools and products in the EarthRef Digital Archive community database will make them useful to other US and international researchers in geo- and paleo-magnetism, and for research and educational purposes at multiple levels. This project will enhance future STEM activities and research through mentoring and training of both graduate and undergraduate students. Part 2: Careful analysis of data uncertainties and improvements in inversion strategies have resulted in greatly improved time varying global spherical harmonic paleomagnetic field models over the time spans from 0-10 ka and 0-100 ka, These models are limited in local temporal and spatial complexity, and do not capture the full complexity of features such as the Levantine spike. However, robust features in the results indicate they can be used as the basis for hypothesis testing about the dynamic structural evolution of the magnetic field. Assuming flux spikes originate as small scale but large amplitude changes at the core-mantle boundary allows quantification of the spatial extent over which changes should be visible at Earth's surface. Paleofield models for 0-10 ka and 0-100 ka will be used to explore two periods of change in geomagnetic dipole moment: (i) the dipole moment decay and subsequent recovery in a period of 20 ky surrounding the Laschamp excursion, and (ii) growth in dipole moment from about 6000 BC to 300 AD and transition to the decay seen in the present field.
来源学科分类	Geosciences - Earth Sciences
文献类型	项目
条目标识符	http://119.78.100.173/C666/handle/2XK7JSWQ/69741
专题	环境与发展全球科技态势
推荐引用方式 GB/T 7714	Catherine Constable.Advances in Paleomagnetic Field Modeling: How does Earth's dipole grow and decay?.2016.