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On the ellipticity of the core-mantle boundary from Earth nutations and gravity

Published online by Cambridge University Press:  03 August 2017

C. F. Yoder  and
E. R. Ivins
C. F. Yoder
Affiliation:
Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, California 91109
E. R. Ivins
Affiliation:
Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, California 91109

Abstract

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A change in the core free nutation period from its hydrostatic value of 466d to about 433d has been inferred from analysis of both earth's annual nutation amplitude from Polaris VLBI data (Herring et al., 1986) and surface gravity in the diurnal tidal band (Zürn et al., 1986; Neuberg et al., 1986). Gwinn et al. (1986) interpret this shift as due to an excess nonhydrostatic ellipticity ed, equivalent to a change in the equatorial minus polar radius of 0.5 km. In this paper, the effect of a layer at the core-mantle boundary (CMB) on σf (and hence ed) is examined. Although the potential effect of this layer on σf is found to be large, constraints imposed from gravimetry limit changes in ed to 10%. In addition, the annual nutation has a significant out-of-phase component. Mantle solid friction accounts for a large fraction of the out-of-phase nutation.

Type
V. Precession & Nutation
Information
Symposium - International Astronomical Union , Volume 128: Earth's Rotation and Reference Frames for Geodesy and Geodynamics , 1988 , pp. 317 - 322
Copyright
Copyright © Reidel 1988 

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