Precession-nutation and the Earth's dynamical flattening
Résumé
From the observed precession of the equator, the luni-solar precession can be deduced by accounting for the direct and indirect planetary effects, for the J_2-tilt effect, for the geodesic precession, for the second order terms called nutation-on-nutation. The luni-solar precession, in turn, is related to the Moon and Sun ephemerides, and this relations depends on the global Earth dynamical flattening H. This is the way one can get a numerical value for H from the observed precession. On the other hand, the dynamical flattening is related to the Earth's main moments of inertia. There is a 1 percent difference between the value of H computed for an Earth model (as PREM) with hydrostatic equilibrium and the observed value. We show here that this difference is solved by adding in the computation of H the mass anomalies inside the mantle as given by seismic tomography and those associated with the flow-induced boundary displacements.