The GFZ IGRF candidate models and an assessment of secular variation predictions

We outline the creation of the GFZ candidate models for the most recent International Geomagnetic Reference Field (IGRF-14), which is the result of an initiative by a working group of the International Association of Geomagnetism and Aeronomy (IAGA) and is based on candidate models from multiple groups worldwide. For IGRF-14, we largely maintained our Mag.num modelling procedure from the previous IGRF-13, but used a selection of models from an ensemble comprised of three variants: a first model covering a longer period (2000-2024) with data from the CHAMP and Swarm satellites and other sources, a second model variant covering only the Swarm era (2014-2024) using Swarm and observatory data, and a third variant using only in-line and cross-track differences from Swarm data. While changes to data selection and the modelling algorithm are minor compared to our previous IGRF generation candidates, we focus here on describing how our final candidates were derived from this set of parent models. In the second part of this article we look back onto candidates for the last IGRF-13 and their secular variation predictions. In light of the data that has become available over time we use current continuous models and the recent, official IGRF-14 as the ground truth to assess the performance of the different secular variation prediction methods.