Geophysical analysis of zonal tidal signals in length of day

Abstract

S U M M A R YThe Earth's zonal response coefficient K is estimated from the tidal signals in the observed length-of-day (LOD) data. Its magnitude and phase are functionals of the Earth's internal structure and dynamics. In this paper, an analysis of 13 years of precise LOD data (1980)(1981)(1982)(1983)(1984)(1985)(1986)(1987)(1988)(1989)(1990)(1991)(1992) reveals strong signals for nine zonal tidal groups ranging from 5 to 35 days in period. Numerical estimates of K for 27 major tides are thus obtained, 11 among which are considered sufficiently high in signal-to-noise ratio to provide meaningful geophysical constraints on the Earth's rotational dynamics. The results favour a K magnitude close to, but somewhat smaller than, 0.315, which is the theoretical value for an elastic mantle completely decoupled from the fluid core plus equilibrium oceans. A small amount of dispersion is also detectable, where shorter periods tend to have lower K magnitude and larger phase lag. Our K magnitude estimates are consistent with two recently published non-equilibrium ocean-tide models and an anelastic response in the mantle, although an equilibrium response in the ocean and a purely elastic response in the mantle is not disallowed. Phase lags of a few degrees are required by both ocean-tide models, and by our data.

Fortnightly Earth rotation, ocean tides and mantle anelasticity

“…Guinot 1970;Yoder et al 1981;Hefty & Capitaine 1990;Robertson et al 1994;Chao et al 1995). Tidal variations in LOD are one of the few mechanisms for probing the solid Earth at frequencies outside the seismic band, but the ocean-tide and elastic body-tide effects on LOD dominate the anelastic effect.…”

Long‐period tidal factors at Antarctica Syowa Station determined from 10 years of superconducting gravimeter data

“… Merriam [1981] investigated the dispersion in the Earth from gravity observations, but met with only limited success at the time; mainly because, only spring gravimeters were employed, the Earth and ocean tide models were primitive, and only diurnal and semidiurnal tides were analyzed. Since the analysis of long‐period tides is a powerful tool for investigating the dissipation in the Earth, previous studies have estimated the Love numbers (h, k), the Earth's zonal response coefficient (κ) and second‐degree zonal geopotential coefficient for lower frequencies from 14 days to 18.6 years [e.g., Smith and Dahlen , 1981; Lambeck and Nakiboglu , 1983; Chao et al , 1995; Zhu et al , 1996; Wu et al , 2001]. …”

Detection of the special gravity signals in sub-tidal band by using wavelet technique

“…(4) By using multi-taper power spectrum for corresponding estimations, the existence of the gravity signals in sub-tidal bands is further determined conveniently [31,32] . This technique uses multiple windows prior to the Fourier transformation to reduce significantly the spectral leakage in order to provide more reliable spectral estimations for determining special gravity oscillation signals.…”

“…The main purpose of this study is to use the WTFS and other techniques to analyse the SG observations with length of 5 years (from January 1, 1998 to December 31,2002), to detect gravity signals in sub-tidal bands associated with possible translational oscillations of the ESIC and to study the properties of these oscillation signals. It is a valuable attempt for developing further theoretical study, for giving valuable attempts in practical detection and also for providing valuable reference in study of Earth's deep interior and its physical properties.…”