GCRAS candidate field models for IGRF-14

We present candidate models for the 14th generation of the International Geomagnetic Reference Field (IGRF-14), specifically the Definitive Geomagnetic Reference Field (DGRF) for epoch 2020.0 and the IGRF for epoch 2025.0. These models were developed using high-quality magnetic measurements from the European Space Agency's Swarm satellite mission, including data from three low-Earth orbiting satellites equipped with Absolute Scalar Magnetometers and Vector Field Magnetometers. These models are part of the CAMPUS project, which is devoted to the construction of a series of Earth’s magnetic field models. Our methodology employs rigorous data selection criteria to minimize contamination from external sources and with strict scalar-vector consistency constraints. The internal magnetic field is parameterized using spherical harmonic functions up to degree 13, with coefficients determined through a two-stage inversion process involving linear inversion of vector measurements followed by nonlinear refinement including absolute scalar intensity data. For the DGRF 2020 model, we utilized data collected between January 2019 and December 2020, while the IGRF 2025 model incorporates measurements from January 2023 to September 2024. Comparison between the models indicates changes in field structure over the five-year interval, particularly in the South Atlantic Anomaly region. These candidate models effectively capture the main features of Earth's core-generated magnetic field and are consistent with long-term trends observed in previous IGRF generations, contributing to the collective scientific effort to maintain accurate descriptions of Earth's magnetic field.