TERRAPUB Earth, Planets and Space

Earth Planets Space, Vol. 62 (No. 10), pp. 787-804, 2010

Evaluation of candidate geomagnetic field models for IGRF-11

C. C. Finlay1, S. Maus2, C. D. Beggan3, M. Hamoudi4, F. J. Lowes5, N. Olsen6, and E. Thébault7

1Earth and Planetary Magnetism Group, Institut ür Geophysik, Sonneggstrasse 5, ETH Zürich, CH-8092, Switzerland
2NOAA/NGDC and CIRES, University of Colorado, U.S.A.
3British Geological Survey, Murchison House, West Mains Road, Edinburgh, EH9 3LA, U.K.
4Helmholtz Centre Potsdam, GFZ German Research centre for Geosciences, Telegrafenberg, 14473, Germany
5School of Chemistry, University of Newcastle, Newcastle Upon Tyne, NE1 7RU, U.K.
6DTU Space, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
7Équipe de Géomagnétisme, Institut de Physique du Globe de Paris, UMR 7154, CNRSINSU, Univ. Paris Diderot, Paris, France

(Received April 20, 2010; Revised September 24, 2010; Accepted November 18, 2010; Online published December 31, 2010)

Abstract: The eleventh generation of the International Geomagnetic Reference Field (IGRF) was agreed in December 2009 by a task force appointed by the International Association of Geomagnetism and Aeronomy (IAGA) Division V Working Group V-MOD. New spherical harmonic main field models for epochs 2005.0 (DGRF-2005) and 2010.0 (IGRF-2010), and predictive linear secular variation for the interval 2010.0-2015.0 (SV-2010-2015) were derived from weighted averages of candidate models submitted by teams led by DTU Space, Denmark (team A); NOAA/NGDC, U.S.A. (team B); BGS, U.K. (team C); IZMIRAN, Russia (team D); EOST, France (team E); IPGP, France (team F); GFZ, Germany (team G) and NASA-GSFC, U.S.A. (team H). Here, we report the evaluations of candidate models carried out by the IGRF-11 task force during October/November 2009 and describe the weightings used to derive the new IGRF-11 model. The evaluations include calculations of root mean square vector field differences between the candidates, comparisons of the power spectra, and degree correlations between the candidates and a mean model. Coefficient by coefficient analysis including determination of weighting factors used in a robust estimation of mean coefficients is also reported. Maps of differences in the vertical field intensity at Earth's surface between the candidates and weighted mean models are presented. Candidates with anomalous aspects are identified and efforts made to pinpoint both troublesome coefficients and geographical regions where large variations between candidates originate. A retrospective analysis of IGRF-10 main field candidates for epoch 2005.0 and predictive secular variation candidates for 2005.0-2010.0 using the new IGRF-11 models as a reference is also reported. The high quality and consistency of main field models derived using vector satellite data is demonstrated; based on internal consistency DGRF-2005 has a formal root mean square vector field error over Earth's surface of 1.0 nT. Difficulties nevertheless remain in accurately forecasting field evolution only five years into the future.
Key words: Geomagnetism, field modelling, reference field, secular variation.

Corresponding author E-mail: cfinlay@erdw.ethz.ch

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