Time-series of the magnetospheric Gauss coefficient |$q_{10}^\mathrm{mag}(t)$| around the 2017 September geomagnetic storm (upper panel) and during magnetic quiet time, in January / February 2018 (lower panel). The four curves in each plot show our model estimates, the estimates with no ionosphere parametrization, the estimates from the CI model and estimates from the CHAOS-7 external field model.