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Earth, Planets and Space
Fig. 2 | Earth, Planets and Space

Fig. 2

From: The Mag.num core field model as a parent for IGRF-13, and the recent evolution of the South Atlantic Anomaly

Fig. 2

Two examples from low-degree coefficients (\(g_1^0\) and \(g_2^0\)) showing the secular variation from IGRF-12 (values for 1997.5 to 2012.5 calculated as linear SV from the adjacent main field coefficients), the Mag.num parent model and the more variable CHAOS-6 model. The red circle indicates our chosen value as predicted secular variation for the coefficients for 2020 to 2025, taken to be the SV of the parent model at epoch 2019.0

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