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Topographic Core-Mantle Coupling and Fluctuations in the Earth's Rotation

Hide, R. and Clayton, R. W. and Hager, B. H. and Spieth, M. A. and Voorhdes, C. V. (1993) Topographic Core-Mantle Coupling and Fluctuations in the Earth's Rotation. In: Relating Geophysical Structures and Processes: The Jeffreys Volume. Geophysical Monograph Series. No.76. American Geophysical Union , Washington, DC, pp. 107-120. ISBN 9780875904672

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Astronomically-determined irregular fluctuations in the Earth's rotation vector on decadal time scales can be used to estimate the fluctuating torque on the lower surface of the Earth's mantle produced by magnetohydrodynamic flow in the underlying liquid metallic core. A method has been proposed for testing the hypothesis that the torque is due primarily to fluctuating dynamic pressure forces acting on irregular topographic features of the core-mantle boundary and also on the equatorial bulge. The method exploits (a) geostrophically-constrained models of fluid motions in the upper reaches of the core based on geomagnetic secular variation data, and (b) patterns of the topography of the CMB based on the mantle flow models constrained by data from seismic tomography, determinations of long wave-length anomalies of the Earth's gravitational field and other geophysical and geodetic data. According to the present study, the magnitude of the axial component of the torque implied by determinations of irregular changes in the length of the day is compatible with models of the Earth's deep interior characterized by the presence of irregular CMB topography of effective “height” no more than about 0.5 km (about 6% of the equatorial bulge) and strong horizontal variations in the properties of the D″ layer at the base of the mantle. The investigation is now being extended to cover a wider range of epochs and also the case of polar motion on decadal time scales produced by fluctuations in the equatorial components of the torque.

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Additional Information:© 1993 by the International Union of Geodesy and Geophysics and the American Geophysical Union. We thank Don Anderson, Jean Dickey, Olafur Gudmundsson, David Stevenson, and Charles Yoder for helpful comments on various aspects of this work. We also thank Dr. Dickey and other members of the Space Geodesy Science and Applications Group of the Jet Propulsion Laboratory for facilitating this collaborative study. Jeremy Bloxham kindly provided coefficients for his core flow model. Partial support was provided by NASA grants NAG5-819 and NAGS-315 to RWC and BHH.
Group:Seismological Laboratory
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Subject Keywords:Earth sciences—Mathematical models; Geophysics—Mathematical models
Record Number:CaltechAUTHORS:20121016-145941398
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Official Citation:Hide, R., R. W. Clayton, B. H. Hager, M. A. Spieth, and C. V. Voorhdes (1993), Topographic core-mantle coupling and fluctuations in the Earth's rotation, in Relating Geophysical Structures and Processes: The Jeffreys Volume, Geophys. Monogr. Ser., vol. 76, edited by K. Aki and R. Dmowska, pp. 107–120, AGU, Washington, D. C., doi:10.1029/GM076p0107.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:34934
Deposited By: Ruth Sustaita
Deposited On:16 Oct 2012 22:56
Last Modified:11 Jun 2015 14:37

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