18.6-yr tidal variations in J2 observed from 48-yr satellite laser ranging (SLR)

SUMMARY Analysis of the 48-yr of satellite laser ranging data of multiple satellites shows that long-term variations in the Earth's dynamical oblateness represented by the second-degree zonal harmonic J2 is best characterized by the superposition of a quadratic trend, 10.5- and 18.6-yr variations. These variations result from climate-related mass changes, tides and core flow-induced variations at the core–mantle boundary. We determined that the global ocean's response to the lunar attraction at the 18.6-yr period is near equilibrium, with an amplitude of 0.4735 ± 0.008 cm and an error of ∼11 per cent relative to the modelled amplitude (0.4224 cm), and ∼2 ± 3 deg of phase lag. The 18.6-yr Love Number was found to be 0.013 75 − i0.005 53 with an error of 2 per cent for both the real and imaginary parts and a phase correction π for the imaginary part of the International Earth Rotation and Reference Systems Service (IERS) 2010 anelasticity model. The nominal frequency-independent anelasticity Love number, k₂, was determined to be 0.3022 ± 0.0001 for the 18.6-yr period, based on a reference frequency of 200 s and α = 0.1514 for mantle anelasticity for mantle anelasticity. This study also reveals a significant gravitational signal (3.06 × 10−11) in J2 obstructs the Earth's mantle anelastic response to the 18.6-yr tidal forces, reflecting in phase shift of π the imaginary part of the IERS 2010 Love number. This signal can be characterized by a positive Love number of 0.011 06 in the modelling of the variation in J2 coupling with the 18.6-yr tide. This signal is possibly produced by the core dynamics, which creates a gravitational signal in J2 with an amplitude of 3.36 × 10−11 at the decadal time scale and could account for ∼70 per cent of the observed 10.5-yr variation