Mean effect of geomagnetic storms on LDM-TEC for a period of 20 days around the onset. Top left: mean differences (Δ) between the modelled and observed LDM-TEC in TECu. Top right: scattering of the differences. Bottom left: mean relative differences (scaled by the observed) in percentage. Bottom right: scattering of the relative differences. The red line is day of the detected onset of the storms.