TERRAPUB Earth, Planets and Space

Earth Planets Space, Vol. 62 (No. 10), pp. 753-763, 2010

IGRF candidate models at times of rapid changes in core field acceleration

Erwan Thébault1, Arnaud Chulliat1, Stefan Maus2, Gauthier Hulot1, Benoit Langlais3, Aude Chambodut4, and Michel Menvielle5

1Équipe de géomagnétisme, Institut de Physique du Globe de Paris, UMR 7154, CNRS-INSU, Univ. Paris Diderot, Paris, France
2National Geophysical Data Center, NOAA E/GC1, 325 Broadway, Boulder, CO 80305, USA
3Laboratoire de Planétologie et Géodynamique de Nantes, UMR 6112, CNRS, Univ. de Nantes, Nantes, France
4Institut de Physique du Globe de Strasbourg, UMR 7516, Université de Strasbourg, Strasbourg, France
5Laboratoire Atmosphéres, Milieux, Observations Spatiales (UMR 8190-CNRS), Paris, France

(Received December 25, 2009; Revised May 10, 2010; Accepted May 17, 2010; Online published December 31, 2010)

Abstract: We submit three candidate models following the call for IGRF-11. We apply a simple modeling approach in spherical harmonics based on a quadratic Taylor expansion for the internal field time variations. We use the Dst magnetic index as a proxy for the external field variations. In order to compensate for the limitations incurred by such a conventional approach, we focus on the optimal selection of satellite data in space and time. We also show that some a priori knowledge about the core field state helps us to avoid the pitfall encountered in the case of rapid changes of core field accelerations. Indeed, various acceleration events of relevance for the IGRF 11th occurred between 2003 and 2010, one of them being a geomagnetic jerk. They could entail disagreements between IGRF candidate models for the secular variation (SV) if data prior to 2008 are used. Our SV and main field (MF) candidate models have a root mean square uncertainty less than 6 nT/yr and 8 nT, respectively, with respect to the modeled magnetic field contributions. These values correspond to the intrinsic error associated with truncating SV and MF models to spherical harmonic degree 8 and 13, respectively, as requested for IGRF models.
Key words: Magnetic field, main field, secular variation, modeling, IGRF, temporal extrapolation, core field acceleration.

Corresponding author E-mail: ethebault@ipgp.fr

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