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the steady part of the secular variation of the earth's magnetic fieldThe secular variation of the Earth's magnetic field results from the effects of magnetic induction in the fluid outer core and from the effects of magnetic diffusion in the core and the mantle. Adequate observations to map the magnetic field at the core-mantle boundary extend back over three centuries, providing a model of the secular variation at the core-mantle boundary. Here we consider how best to analyze this time-dependent part of the field. To calculate steady core flow over long time periods, we introduce an adaptation of our earlier method of calculating the flow in order to achieve greater numerical stability. We perform this procedure for the periods 1840-1990 and 1690-1840 and find that well over 90 percent of the variance of the time-dependent field can be explained by simple steady core flow. The core flows obtained for the two intervals are broadly similar to each other and to flows determined over much shorter recent intervals.
Document ID
19930037356
Document Type
Reprint (Version printed in journal)
Authors
Bloxham, Jeremy
(Harvard Univ. Cambridge, MA, United States)
Date Acquired
August 16, 2013
Publication Date
December 10, 1992
Publication Information
Publication: Journal of Geophysical Research
Volume: 97
Issue: B13
ISSN: 0148-0227
Subject Category
GEOPHYSICS
Funding Number(s)
CONTRACT_GRANT: NSF EAR-90-18620
CONTRACT_GRANT: NSF EAR-88-04618
CONTRACT_GRANT: NAG5-918
CONTRACT_GRANT: NSF EAR-91-58298
CONTRACT_GRANT: NAG5-1369
Distribution Limits
Public
Copyright
Other