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DOI	10.1073/pnas.1717454115
	Geomagnetic polar minima do not arise from steady meridional circulation
	Cao H.; Yadav R.K.; Aurnou J.M.
发表日期	2018
ISSN	0027-8424
起始页码	11186
结束页码	11191
卷号	115 期号:44
英文摘要	Observations of the Earth's magnetic field have revealed locally pronounced field minima near each pole at the core-mantle boundary (CMB). The existence of the polar magnetic minima has long been attributed to the supposed large-scale overturning circulation of molten metal in the outer core: Fluid upwells within the inner core tangent cylinder toward the poles and then diverges toward lower latitudes when it reaches the CMB, where Coriolis effects sweep the fluid into anticyclonic vortical flows. The diverging near-surface meridional circulation is believed to advectively draw magnetic flux away from the poles, resulting in the low intensity or even reversed polar magnetic fields. However, the interconnections between polar magnetic minima and meridional circulations have not to date been ascertained quantitatively. Here, we quantify the magnetic effects of steady, axisymmetric meridional circulation via numerically solving the axisymmetric magnetohydrodynamic equations for Earth's outer core under the magnetostrophic approximation. Extrapolated to core conditions, our results show that the change in polar magnetic field resulting from steady, large-scale meridional circulations in Earth's outer core is less than 3% of the background field, significantly smaller than the100% polar magnetic minima observed at the CMB. This suggests that the geomagnetic polar minima cannot be produced solely by axisymmetric, steady meridional circulations and must dependuponadditional tangent cylinder dynamics, likely including nonaxisymmetric, time-varying processes. © 2018 National Academy of Sciences. All rights reserved.
英文关键词	Flow magnetic field interactions; Geodynamo; Gyroscopic pumping; Polar magnetic minima; Polar vortex
语种	英语
scopus关键词	article; magnetic field; quantitative analysis
来源期刊	Proceedings of the National Academy of Sciences of the United States of America
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/160449
作者单位	Cao, H., Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, United States, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, United States; Yadav, R.K., Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, United States; Aurnou, J.M., Department of Earth Planetary and Space Sciences, University of California, Los Angeles, CA 90095, United States
推荐引用方式 GB/T 7714	Cao H.,Yadav R.K.,Aurnou J.M.. Geomagnetic polar minima do not arise from steady meridional circulation[J],2018,115(44).
APA	Cao H.,Yadav R.K.,&Aurnou J.M..(2018).Geomagnetic polar minima do not arise from steady meridional circulation.Proceedings of the National Academy of Sciences of the United States of America,115(44).
MLA	Cao H.,et al."Geomagnetic polar minima do not arise from steady meridional circulation".Proceedings of the National Academy of Sciences of the United States of America 115.44(2018).