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Candidate models for the 13th generation International Geomagnetic Reference Field are being evaluated.

Gillet Finlay

 The International Association of Geomagnetism and Aeronomy (IAGA) Division V Working Group V-MOD published the 13th revision of the International Geomagnetic Reference Field (IGRF) in December 2019. This revision includes two new spherical harmonic main field models for the epochs 2015.0 (DGRF-2015) and 2020.0 (IGRF-2020), as well as a model of predicted secular variation for the period 2020.0 to 2025.0. (SV-2020-2025). Candidates submitted by fifteen international teams were used to create the models. The differences between the majority of candidates can be explained primarily by individual modelling methodologies and data selection strategies. None of the candidates were so dissimilar that they should have been excluded from the final IGRF-13 As a result, the IAGA V-MOD task force chose two approaches: the median of the Gauss coefficients of the candidates for the DGRF-2015 and IGRF-2020 models, and the robust Huber-weighted model for the predictive SV-2020-2025 model. In this paper, we describe the evaluation of the candidate models and the methodology followed to derive the final IGRF-13 products.