Climatological models of non-polar geomagnetic daily variations using the DIFI methodology with Swarm and CHAMP satellite data

Climatological models of non-polar geomagnetic daily variations are valuable tools for applications ranging from studying ionospheric current systems to correcting magnetic field survey data. Several such models have been developed as part of the Dedicated Ionospheric Field Inversion (DIFI) project during the Swarm satellite mission. Here, we present the latest version of the DIFI model, DIFI-8, derived from ten years of magnetic field measurements by the Swarm Alpha and Bravo satellites (2014–2023), supplemented with data from ground-based observatories. We also introduce an updated version of the extended DIFI model, xDIFI-2, constructed using data from Swarm, CHAMP, and ground-based observatories, and covering the period from 2001 to 2023. As with previous versions, these models provide estimates of both the primary and induced magnetic fields generated by mid-latitude solar quiet (Sq) currents and the Equatorial Electrojet (EEJ) within ±55 degrees quasi-dipole (QD) latitudes, at both ground and Low-Earth Orbit (LEO) satellite altitudes. In addition, DIFI-8 incorporates corrections for toroidal magnetic fields based on a recently published climatological model. Both models have been extensively validated using independent ground-based observatory data. The equivalent current systems and total current intensities derived from DIFI-8 and xDIFI-2 are consistent over the two-decade period, suggesting that these models may be reliably applied even outside their formal domain of validity, with minimal additional error.