Superposed epoch statistics of US power-grid disturbances for days of geomagnetic activity as measured by the maximum dB/dt in 30-min intervals, averaged for the US BOU and FRD stations (〈|dB/dt(30 m)|〉) for the top 2, 5, and 10% of dates between 1992 and 2010, respectively. In each panel, the horizontal gray line and the dashed lines adjacent to it show the disturbance rates under quiescent space-weather conditions (i.e., the values of g_i, see Sect. 3 and Table 1) and the associated standard deviations, respectively.