Fig. 4From: A secular variation candidate model for IGRF-13 based on Swarm data and ensemble inverse geodynamo modellingSecular variation spectra at the Earth’s surface. Each thin red line corresponds to an ensemble member, prior to the ingestion of the initial model for 2019.0. The blue envelope is that defined by the initial model plus or minus one standard deviation. In black, the envelope defined by the mean of the ensemble plus or minus one standard deviationBack to article page