A diurnal resonance in the ocean tide and in the Earth's load response due to the resonant free ‘core nutation’

TLDR

The Earth's rotating, elliptical fluid core causes the luni‑solar forced nutations and body tide to resonate near (1 + 1/460) cycle sidereal day⁻¹. The authors demonstrate that ocean tides and the Earth's response to them must also resonate at (1 + 1/460) cycle day⁻¹. They examine how these resonant oceanic effects influence the Earth's nutational motion and the body tide. The resonant oceanic effects can alter forced nutations by up to 0.002 arcsec over an 18.6‑yr period and perturb the observed body‑tide resonance, with tidal‑gravity differences between K1 and O1 potentially increased by 30 % or more.

Abstract

The luni-solar forced nutations and body tide are believed to be resonant at frequencies near (1 + 1/460) cycle sidereal day−1 as seen from the rotating Earth. This resonance is due to the Earth's rotating, elliptical fluid core. We show here that tides in the open ocean and the Earth's response to those tides must also be resonant at (1 + 1/460) cycle day−1. We examine these resonant oceanic effects on the Earth's nutational motion and on the body tide. Effects on the forced nutations might be as large as 0.002 arcsec at 18.6 yr. The effects on the observed resonance in the body tide are more important. For tidal gravity, for example, the difference between K1 and 01 which is usually used to determine the resonance, can be perturbed by 30 per cent or more due to the oceanic resonance effects.