Fig. 4From: The 2014 geomagnetic jerk as observed by southern African magnetic observatoriesSecular variation of the Z component between 2006 and 2015. The black dots show monthly mean secular variation estimates derived as running annual differences. The CHAOS-6 (green line) and the POMME 10 model (black dashes) predictions are included, while piecewise linear fits to the data provide estimates of secular acceleration as given in the legendsBack to article page