Variations of the Earth's figure axis from satellite laser ranging and GRACE

Abstract

[1] Satellite laser ranging (SLR) data were used to determine the variations in the Earth's principal figure axis represented by the degree 2 and order 1 geopotential coefficients: C 21 and S 21 . Significant variations at the annual and Chandler wobble frequencies appear in the SLR time series when the rotational deformation or "pole tides" (i.e., the solid Earth and ocean pole tides) were not modeled. The contribution of the ocean pole tide is estimated to be only ∼8% of the total annual variations in the normalized coefficients: C 21 /S 21 based on the analysis of SLR data. The amplitude of the nontidal annual variation of C 21 is only ∼ 30% of S 21 from the SLR time series. The estimates of the annual variation in S 21 from SLR, the Gravity Recovery and Climate Experiment (GRACE) and polar motion excitation function, are in a good agreement. The nature of the linear trend for the Earth's figure axis determined by these techniques during the last several years is in general agreement but does not agree as well with results predicted from current glacial isostatic adjustment (GIA) models. The "fluid Love number" for the Earth is estimated to be ∼0.9 based on the position of the mean figure axis from the GRACE gravity model GGM03S and the mean pole defined by the IERS 2003 conventions. The estimate of C 21 /S 21 from GRACE and SLR provides an improved constraint on the relative rotation of the core. The results presented here indicate a possible tilt of the inner core figure axis of ∼2°and ∼3 arc sec displacement for the figure axis of the entire core.

Realizing a terrestrial reference frame using the Global Positioning System

“…While the oblateness (J 2 ) term and its time derivative are based mainly on multidecadal SLR observations [Tapley et al, 2005;Nerem et al, 1993], GPS data collected in LEO could also be used to provide these estimates [e.g., Lin et al, 2012]. Rates for the degree 2, order 1 terms are set according to the IERS 2003 standards [McCarthy and Petit, 2003] and represent long-term motion of the Earth's principal figure axis [e.g., Cheng et al, 2011]. From the perspective of the TRF, these correspond to pure rotations and should have negligible influence on the realization of geocenter and scale in our network-free approach.…”

Earth’s Rotation: A Challenging Problem in Mathematics and Physics

“…ESCAPA et al (2001) derived a solution to the linearised equations, which gives the frequencies of the four normal modes or free harmonic oscillations of the rotation pole in terms of the ellipticities and an additional small parameter d: (CHENG and TAPLEY 2004;CHENG et al 2011;COX and CHAO 2002), and other time variations of the geopotential as unaccounted effects of tidal models (FERRÁ NDIZ et al 2011), etc. The Hamiltonian method provided a systematic, consistent procedure to approach all of them in the non-steady, non-rigid case.…”

Total Discharge Estimation in the Korean Peninsula Using Multi-Satellite Products

“…Each time-variable gravity field is truncated up to 60 degrees and orders in terms of spherical harmonic coefficients. Gaussian filtering (300 km) and the C 20 coefficient from Satellite Laser Ranging (SLR) are applied to reduce noise [22,23]. The GRACE RL05 gravity anomaly can be recovered based on surface mass changes in terms of equivalent water thickness, and it may be expressed as the terrestrial water storage anomaly (TWSA; Equation (2)).…”