Magnetograms from selected stations of the IMAGE magnetometer network. Each coloured curve represents one station, with KEV being the northernmost station and KAR being the southernmost. The shaded areas refer to the three observed spikes over Fennoscandia. The vertical dashed and solid orange numbered lines mark the times before and at the maximum of the electrojet enhancement respectively. They also refer to the total equivalent currents shown in the six right panels in Figure 3.