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Characterization and implications of intradecadal variations in length of day

Abstract

Variations in Earth's rotation (defined in terms of length of day) arise from external tidal torques, or from an exchange of angular momentum between the solid Earth and its fluid components1. On short timescales (annual or shorter) the non-tidal component is dominated by the atmosphere, with small contributions from the ocean and hydrological system. On decadal timescales, the dominant contribution is from angular momentum exchange between the solid mantle and fluid outer core. Intradecadal periods have been less clear and have been characterized by signals with a wide range of periods and varying amplitudes, including a peak at about 6 years (refs 2, 3, 4). Here, by working in the time domain rather than the frequency domain, we show a clear partition of the non-atmospheric component into only three components: a decadally varying trend, a 5.9-year period oscillation, and jumps at times contemporaneous with geomagnetic jerks. The nature of the jumps in length of day leads to a fundamental change in what class of phenomena may give rise to the jerks, and provides a strong constraint on electrical conductivity of the lower mantle, which can in turn constrain its structure and composition.

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Figure 1: Fit to ΔLOD data (black line) of 5.9-year oscillation and decadal trend (grey line).
Figure 2: Decadally detrended LOD data (with 6-month running average), plotted with 5.9-year oscillation fit (dashed line).
Figure 3: Focus on 1965–1985 to show correlation between the 5.9-year LOD oscillation and a histogram of wavelet-determined geomagnetic jerk occurrence times10.
Figure 4: Focus on 2002–2006 to compare LOD series with well-constrained geomagnetic jerk times (long vertical dashes; short dashes mark 3 months each side of these times).

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Acknowledgements

O.d.V. was supported by Centre National d’Études Spatiales (CNES) through the TOSCA (Terre, Océan, Surfaces Continentales, Atmosphère) programme, and by the French Institut Universitaire de France. The oceanographic model used is a contribution of the Consortium for Estimating the Circulation and Climate of the Ocean (ECCO) funded by the National Oceanographic Partnership Program.

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R.H. performed the primary analysis and led the writing of the manuscript. O.d.V. provided the original data with corrections for atmosphere and ocean, and contributed to writing the manuscript.

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Correspondence to R. Holme.

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Holme, R., de Viron, O. Characterization and implications of intradecadal variations in length of day. Nature 499, 202–204 (2013). https://doi.org/10.1038/nature12282

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