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| Titel |
The geomagnetic secular-variation timescale in observations and numerical dynamo models |
| VerfasserIn |
Florian Lhuillier, Alexandre Fournier, Gauthier Hulot, Julien Aubert |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250045945
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| Zusammenfassung |
| The knowledge of the spatial power spectra Rn of the main geomagnetic field and Qn of its
secular variation makes it possible to define typical timescales Ïn = (Rn-Qn)1-2 for each
spherical harmonic degree n. Investigating both observations and numerical dynamo
models, we test the relevance of a one-parameter law of the form Ïn = ÏSV -n
in contrast to a two-parameter law of the form Ïn = α à nγ. We show that the
one-parameter law is satisfied for the non-dipole field, given the statistical way the
observed Ïn are expected to fluctuate, and moreover well-suited to describe the
intrinsic behaviour of a dynamo. For recent satellite field models, we thus find a value
ÏSV - 470 ±6590Â yr, when considering degrees n = 3 to 10. Given the agreement found
between instantaneous and time-averaged estimates of ÏSV in numerical dynamos, we expect
the above figure to be appropriate to describe the dynamics of the geomagnetic field on
timescales much longer than that of the historical record. The secular-variation timescale
ÏSV has already been used in systematic studies to estimate typical quantities of
the Earth’s dynamo. In the broader context of geomagnetic data assimilation, and
under the assumption that the Earth and a given numerical dynamo share the same
asymptotic behaviour as regards the secular-variation timescales, ÏSV could provide a
sensible and convenient means to rescale the time axis of dynamo simulations. |
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