In:
Journal of Geophysical Research: Solid Earth, American Geophysical Union (AGU), Vol. 102, No. B12 ( 1997-12-10), p. 27659-27687
Abstract:
There are differences between the observed values of nutation and the computed ones based on the International Astronomical Union (IAU) 1980 adopted nutation series. These differences can be expressed in the frequency domain where they may reach several milliarc seconds, a level that is too large for practical use. This paper aims to resolve part of these differences by computing a new theoretical model accounting for additional geophysical effects. A new transfer function is computed, based on an Earth initially in a nonhydrostatic equilibrium corresponding to the steady state associated with the present mantle convection. The mantle mass anomalies are deduced from seismic tomography data, and the flow‐induced boundary deformations are computed from internal loading for an Earth made up of a viscous inner core, a liquid outer core, a viscous mantle, and a solid lithosphere. In this way, a new core‐mantle boundary (CMB) flattening is obtained, which gives the observed free core nutation (FCN) period. Furthermore, the global Earth dynamical flattening induced by the mass anomalies in the mantle associated with tomography and by the mass anomalies due to the computed boundary deformations, is in agreement with the J 2 form factor (or the observed precession constant). In addition to this nonhydrostatic initial state, the rheology of the mantle is considered as inelastic. The transfer function for nutation is then obtained by numerical integration of motion equations from the Earth's center up to the surface to provide a model which is completely self‐consistent. In order to validate our model, the transfer function is convolved with new rigid Earth nutations, ocean corrections are applied and the final results are then compared with the observed nutations or with the International Earth Rotation Service (IERS) nutation series. The residuals between our model and the observation are about 3 times smaller than those between the IAU 1980 adopted model and the observation. However, our model still presents residuals above the observational error; this is particularly true for the out‐of‐phase part of the residuals, while the in‐phase part gives very small residuals (improvement of about 1 order of magnitude). A further step in this study is a refinement of the modeling of geophysical fluids (core, ocean, and atmosphere).
Type of Medium:
Online Resource
ISSN:
0148-0227
Language:
English
Publisher:
American Geophysical Union (AGU)
Publication Date:
1997
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