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Limits on lateral density and velocity variations in the Earth's outer core

Stevenson, D. J. (1987) Limits on lateral density and velocity variations in the Earth's outer core. Geophysical Journal International, 88 (1). pp. 311-319. ISSN 0956-540X. https://resolver.caltech.edu/CaltechAUTHORS:20131120-103707567

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Abstract

An approximate analysis is given for the likely fractional lateral density variations (δρ/ρ) in the outer core, caused by large scale-length fluid dynamical processes. It is first shown that fractional density and fractional seismic velocity variations are probably comparable, so that fluid dynamic arguments have relevance to seismic data. In regions of nearly neutral stability in the outer core, an analysis of convective vigour indicates an upper bound of δρ/ρ≲10^(−8). If the outer core possesses one or more layers of strong static stability then stationary contributions to δρ can be larger, if they are associated with axisymmetric (m = 0) harmonics, because of stabilizing zonal winds. Baroclinic instabilities nevertheless limit δρ/ρ≲ 10^(−6) but may not exist if the static stability is sufficiently large. Shear instabilities always limit δρ/ρ≲ 10^(−4). Magnetic field effects suggest comparable or more stringent upper bounds. It is concluded that scientists undertaking analysis of the Earth's geoid or seismic travel times or normal modes can safely assume that there are negligible lateral variations in the outer core.


Item Type:Article
Related URLs:
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http://dx.doi.org/10.1111/j.1365-246X.1987.tb01383.xDOIArticle
ORCID:
AuthorORCID
Stevenson, D. J.0000-0001-9432-7159
Additional Information:© 1987 Royal Astronomical Society. Accepted 1986 July 28. Received 1986 June 20; in original form 1986 January 9. Article first published online: 2 Apr 2007. This research was supported by the NSF. I thank M. Richards for useful discussions and for providing part of the motivation for this note, D. L. Anderson for his spirited criticism, and the referees for their pursuit of clarity and exactitude. Contribution number 4290 from the Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California 91125.
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Subject Keywords: core; density; fluid velocity; lateral inhomogeneity
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Caltech Division of Geological and Planetary Sciences4290
Issue or Number:1
Record Number:CaltechAUTHORS:20131120-103707567
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20131120-103707567
Official Citation:Stevenson, D. J. (1987), Limits on lateral density and velocity variations in the Earth's outer core. Geophysical Journal of the Royal Astronomical Society, 88: 311–319. doi: 10.1111/j.1365-246X.1987.tb01383.x
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:42593
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:20 Nov 2013 20:48
Last Modified:03 Oct 2019 06:00

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