摘要：The occurrence of geomagnetically induced currents (GICs) poses serious threats to modern technological infrastructure. Large GICs result from sharp variations of the geomagnetic field (dB/dt) caused by changes of large-scale magnetospheric and ionospheric currents. Intense dB/dt perturbations are known to occur often in high-latitude regions as a result of storm time substorms. Magnetospheric compressions usually caused by interplanetary shocks increase the magnetopause current leading to dB/dt perturbations more evident in midlatitude to low-latitude regions, while they increase the equatorial electrojet current leading to dB/dt perturbations in dayside equatorial regions. We investigate the effects of shock impact angles and speeds on the subsequent dB/dt perturbations with a database of 547 shocks observed at the L1 point. By adopting the threshold of dB/dt = 100 nT/min, identified as a risk factor to power systems, we find that dB/dt generally surpasses this threshold when following impacts of high-speed and nearly frontal shocks in dayside high-latitude locations. The same trend occurs at lower latitudes and for all nightside events but with fewer high-risk events. Particularly, we found nine events in equatorial locations with dB/dt > 100 nT/min. All events were caused by high-speed and nearly frontal shock impacts and were observed by stations located around noon local time. These high-risk perturbations were caused by sudden strong and symmetric magnetospheric compressions, more effectively intensifying the equatorial electrojet current, leading to sharp dB/dt perturbations. We suggest that these results may provide insights for GIC forecasting aiming at preventing degradation of power systems due to GICs.
