Fast torsional waves and strong magnetic field within the Earth’s core

Nicolas Gillet (), Dominique Jault, Elisabeth Canet and Alexandre Fournier
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Nicolas Gillet: Laboratoire de Géophysique Interne et Tectonophysique, CNRS, Université Joseph Fourier, BP 53, 38041 Grenoble cedex 9, France
Dominique Jault: Laboratoire de Géophysique Interne et Tectonophysique, CNRS, Université Joseph Fourier, BP 53, 38041 Grenoble cedex 9, France
Elisabeth Canet: Laboratoire de Géophysique Interne et Tectonophysique, CNRS, Université Joseph Fourier, BP 53, 38041 Grenoble cedex 9, France
Alexandre Fournier: Equipe de Géomagnétisme, Institut de Physique du Globe de Paris, Université Paris-Diderot, CNRS, 4 place Jussieu, F-75252 Paris cedex 5, France

Nature, 2010, vol. 465, issue 7294, 74-77

Abstract: Earth's core strength There is no direct way of measuring the magnetic field within the Earth's fluid outer core, which generates the magnetic field that we can measure. Indirect methods of calculating the interior field strength have yielded contradictory results. Observations of Earth's length of day at a period of 60 years have been used to provide an estimate of only ∼0.2 millitesla for the internal field, whereas numerical geodynamo models predict an inner field an order of magnitude larger. Nicolas Gillet and colleagues now use models of fluid flow in the core to resolve this discrepancy. They focus on an unexplained peak in quasi-geostrophic oscillations seen at around 6 years, a product of fast torsional waves generated by intercommunication of angular momentum between the core and the overlying solid mantle. From this they estimate an outer-core magnetic field strength of ∼4 millitesla, consistent with that predicted by geodynamo simulations.

Date: 2010
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DOI: 10.1038/nature09010

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