Graphical rendition of the grid-disturbance rates under different levels of geomagnetic activity, as listed in Table 1. The three columns show the results for geomagnetic activity in the 10th, 5th, and 2nd upper percentiles of geomagnetic activity as measured by |dB/dt(30 m)|, respectively. The excess in event frequency on geomagnetically active days compared to nearby inactive days is shown by dark diagonal shading.