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Quasi-geostrophic flows responsible for the secular variation of the Earth's magnetic field

Abstract : We present core flows constructed from high resolution secular variation (SV) models for the epochs 2001, 2002.5 and 2004, assuming that these flows are quasi-geostrophic in the core interior and that they do not cross the axial cylindrical surface tangent to the inner core. A large jet encircling the inner core and carrying a significant part of the core angular momentum and axial vortices of ∼700 km diameter mainly clustering around the cylinder tangent to the solid inner core, are inferred from geomagnetic SV. New regularizations are suggested from dynamic considerations. It is found that medium and small-scale velocity fields contribute significantly to the large-scale SV. Accordingly, final models of core flows are calculated after an iterative process, whereby the magnetic field variation produced by small-scale stochastic magnetic fields and medium to small-scale computed velocity fields are incorporated into the inversion itself as modelling errors. This study represents a significant step in an effort to join geomagnetic observations and the fluid core dynamics on short timescales.
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M. A. Pais, Dominique Jault. Quasi-geostrophic flows responsible for the secular variation of the Earth's magnetic field. Geophysical Journal International, Oxford University Press (OUP), 2008, 173 (2), pp.421 à 443. ⟨10.1111/j.1365-246X.2008.03741.x⟩. ⟨insu-00335299⟩



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