Trying to figure out relationship between LOD and non-equilibrium ocean tides
Chih-Wei Chou
Abstract:
The Earthˇ¦s zonal response coefficient Łeis estimated from the tidal signals in the observed length-of-day (LOD) data. Its magnitude and phase are functionals of the Earthˇ¦s internal structure and dynamics. We analyze 13 years of precise LOD data (1980-1992) reveals strong signals for nine zonal tidal groups ranging from 5 to 35 days in period. Numerical estimates ofŁefor 27 major tides are thus obtained, 11 among which are considered sufficiently high in SNR to provide meaningful geophysical constraints on the Earthˇ¦s rotational dynamics. The results favor aŁemagnitude 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 lowerŁemagnitude and larger phase lag. OurŁemagnitude 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.
Reference:
Chao, B.F., Merriam, J.B. & Tamura, Y., 1995. Geophysical analysis of zonal tidal signals in length of day, Geophys. J. Int., 122, 765^775.
Wahr, J.M. & Bergen, Z., 1986. The effects of mantle anelasticity on nutations, Earth tides, and tidal variations of rotation rate, Geophys. J. R. astr. Soc., 87, 633^668.
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