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The geomagnetic secular‐variation timescale in observations and numerical dynamo models
Author(s) -
Lhuillier Florian,
Fournier Alexandre,
Hulot Gauthier,
Aubert Julien
Publication year - 2011
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 - 10.1029/2011gl047356
Subject(s) - dynamo , earth's magnetic field , secular variation , geomagnetic secular variation , dynamo theory , physics , dipole , data assimilation , context (archaeology) , geophysics , variation (astronomy) , statistical physics , magnetic field , geodesy , geology , astrophysics , meteorology , geomagnetic storm , quantum mechanics , paleontology
The knowledge of the spatial power spectra of the main geomagnetic field and of its secular variation makes it possible to define typical timescales τ n for each spherical harmonic degree n . Investigating both observations and numerical dynamos, we show that a one‐parameter law of the form τ n = τ SV / n is satisfied for the non‐dipole field, given the statistical way the observed τ n are expected to fluctuate. Consequently, we determine the corresponding secular‐variation timescale τ 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, τ SV could provide a sensible and convenient means to rescale the time axis of dynamo simulations.