Pure and Applied Geophysics

, Volume 175, Issue 5, pp 1599–1609 | Cite as

An Improbable Observation of the Diurnal Core Resonance

  • Duncan Carr AgnewEmail author


The resonance associated with the ellipticity of the core-mantle boundary is usually measured with observations of either the Earth’s nutations, or of tidal gravity, strain, or tilt. But, improbably, it can also be seen in a dataset collected and processed with older and simpler technologies: the harmonic constants for the ocean tides. One effect of the resonance is to decrease the ratio of the amplitude of the \(\mathrm{ P_1}\) constituent to the amplitude of the \(\mathrm{ K_1}\) constituent to 0.96 of the ratio in the equilibrium tidal potential. The compilation of ocean-tide harmonic constants prepared by the International Hydrographic Bureau between 1930 and 1980 shows considerable scatter in this ratio; however, if problematic stations and regions are removed, this dataset clearly shows a decreased ratio. While these data apply only a weak constraint to the frequency of the resonance, they also show that the effect could have been observed long before it actually was.


Nearly diurnal free wobble ocean tides 



I thank Bernie Zetler for making NOAA’s copy of the IHO Data Bank tape available to me in 1981, and Walter Zürn and Richard Ray for comments on an early draft of this paper. Spherical-harmonic expansions of modern tide models are from Richard Ray at, and his recent paper on tidal inference stimulated me to write this one.


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Copyright information

© Springer International Publishing 2017

Authors and Affiliations

  1. 1.Institute of Geophysics and Planetary Physics, Scripps Institution of OceanographyUniversity of California San DiegoLa JollaUSA

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