Fig. 4From: A regional geomagnetic field model over Southern Africa derived with harmonic splines from Swarm satellite and ground-based data recorded between 2014 and 2019The secular variation trend in X, Y and Z field components between 2015.0 and 2019.0 from the four INTERMAGNET observatories, HER, HBK, TSU and KMH (black dots), with the two models, CHAOS-6- × 9 (blue) and SACFM-3 (red). Gray lines represent piecewise linear fits to highlight abrupt changes of trendBack to article page