DOI: 10.1073/pnas.1717454115
论文题名: Geomagnetic polar minima do not arise from steady meridional circulation
作者: Cao H. ; Yadav R.K. ; Aurnou J.M.
刊名: Proceedings of the National Academy of Sciences of the United States of America
ISSN: 0027-8424
出版年: 2018
卷: 115, 期: 44 起始页码: 11186
结束页码: 11191
语种: 英语
英文关键词: Flow magnetic field interactions
; Geodynamo
; Gyroscopic pumping
; Polar magnetic minima
; Polar vortex
Scopus关键词: article
; magnetic field
; quantitative analysis
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. Citation statistics:
资源类型: 期刊论文
标识符: http://119.78.100.158/handle/2HF3EXSE/163644
Appears in Collections: 气候变化与战略
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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
Recommended Citation:
Cao H.,Yadav R.K.,Aurnou J.M.. Geomagnetic polar minima do not arise from steady meridional circulation[J]. Proceedings of the National Academy of Sciences of the United States of America,2018-01-01,115(44)