Upper. The variation of the auroral electrojet intensity index, SML, with the upstream solar wind Poynting flux transfer to the magnetosphere, ε, (black diamonds). The lower boundary is highlighted through a simple linear relationship (SML(ε) = −0.12 × Epsilon; red asterisks). Lower. Plot showing the time variation of SML (black line) and the solar wind forcing component, i.e., the SML(ε), (red line) during the 7–8 September 2017 geomagnetic storm period, with intervals 1 and 2 indicated.