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The strength of gravitational core‐mantle coupling
Author(s) -
Davies Christopher J.,
Stegman Dave R.,
Dumberry Mathieu
Publication year - 2014
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2014gl059836
Subject(s) - mantle (geology) , geoid , inner core , geology , core–mantle boundary , mantle convection , geophysics , hotspot (geology) , outer core , physics , geodesy , earth's rotation , angular momentum , seismic tomography , seismology , lithosphere , classical mechanics , tectonics , measured depth
Gravitational coupling between Earth's core and mantle has been proposed as an explanation for a 6 year variation in the length‐of‐day (ΔLOD) signal and plays a key role in the possible superrotation of the inner core. Explaining the observations requires that the strength of the coupling, Γ, falls within fairly restrictive bounds; however, the value of Γ is highly uncertain because it depends on the distribution of mass anomalies in the mantle. We estimate Γ from a broad range of viscous mantle flow models with density anomalies inferred from seismic tomography. Requiring models to give a correlation larger than 70% to the surface geoid and match the dynamic core‐mantle boundary ellipticity inferred from Earth's nutations, we find that 3 × 10 19 <Γ<2 × 10 20 N m, too small to explain the 6 year ΔLOD signal. This new constraint on Γ has important implications for core‐mantle angular momentum transfer and on the preferred mode of inner core convection.