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The geomagnetic secular-variation timescale in observations and numerical dynamo models

Abstract : The knowledge of the spatial power spectra of the main geomagnetic field and of its secular variation makes it possible to define typical timescales t n for each spherical harmonic degree n. Investigating both observations and numerical dynamos, we show that a one‐parameter law of the form t n = t SV/n is satisfied for the non‐dipole field, given the statistical way the observed t n are expected to fluctuate. Consequently, we determine the corresponding secular‐ variation timescale t SV from either instantaneous or time‐ averaged spectra, leading to a value of 415 ± 45 55 yr for recent satellite field models. In the broader context of geomagnetic data assimilation, t SV could provide a sensible and convenient means to rescale the time axis of dynamo simulations.
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Florian Lhuillier, Alexandre Fournier, Gauthier Hulot, Julien Aubert. The geomagnetic secular-variation timescale in observations and numerical dynamo models. Geophysical Research Letters, American Geophysical Union, 2011, 38 (9), pp.L09306. ⟨10.1029/2011GL047356⟩. ⟨insu-01410184⟩

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