Effect of the fluid core on changes in the length of day due to long period tides

Abstract

Summary. The long period luni‐solar tidal potential is known to cause periodic changes in the Earth's rotation rate. We find that the effect of a dissipationless fluid outer core is to reduce the amplitudes of these tidal perturbations by ∼ 11 per cent. When the fluid core effect is added to Agnew & Farrell's estimate of the effect of an equilibrium ocean, the result is in accord with observation. The effects of dissipative processes within the fluid core are also examined. We find out‐of‐phase perturbations which could be as large as ∼ 10ms at 18.6 yr. We conclude, however, that the poorly understood decade fluctuations in the Earth's rotation rate will prohibit observation of this effect. Copyright © 1981, Wiley Blackwell. All rights reserved