Geomagnetic field residuals from CHAMP satellite: essential for revealing unmodelled sources

Recently, due to more than a decade of magnetic measurements obtained from LEO (low Earth orbit) satellites, more robust global geomagnetic field models have been produced. Generally, these models are based on data selected on specific criteria, as night-side and quiet-time measurements to get the best possible description of the internal contributions and to minimise the ionospheric and magnetospheric effects. Despite recent efforts, the external fields contributions remain poorly modelled and clearly understood. Here, we propose to estimate the unmodelled signals mainly linked to the external magnetic fields. We compute residuals from the available daytime and night-time original CHAMP (CHAllenging Minisatellite Payload) satellite data and GRIMM-3 model. The post-processing of residuals and the residuals distribution for all geomagnetic field components offer us the possibility to investigate some of their specific features, important to be considered when internal field models are computed.