Long-period variations in gravity field caused by mantle anelasticity

A numerical perturbation approach is used to assess the effect of mantle anelasticity on the Earth's zonal response coefficient kappa, the zonal geopotential coefficient J(2), and the orbital node of geodetic satellites. The theoretical predictions are used to compare solutions of elastic ocean tide models and tides observed by geodetic satellites for M(f), M(m), S-sa, and S-a. The discrepancies between the satellite observed tides and the solution from Schwiderski and recent altimetric ocean tide models can be partly explained by the predicted effect of mantle anelasticity at M(f) and M(m) frequencies. Approximately 80% of the observed semiannual variation in delta J(2) by geodetic satellites can be attributed to the tidal deformation from anelasticity and from the classical equilibrium ocean. The predicted kappa for the 18.6-year tide was computed for an Earth with an anelastic mantle and a nonequilibrium ocean. The range of the lower and upper bounds of kappa for the 18.6-year tide is from 0.345 to 0.377 in amplitude, and from -6 degrees to 3 degrees in phase, with preferred amplitude of 0.365 and phase of -0 degrees 8.