Geomagnetically Induced Currents Caused by Interplanetary Shocks with Different Impact Angles and Speeds

The occurrence of geomagnetically induced currents (GICs) poses serious threats to modern technological infrastructure. Large GICs result from sharp variations of the geomagnetic field (dBdt) caused by changes of large-scale magnetospheric and ionospheric currents. Intense dBdt 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 dBdt perturbations more evident in midlatitude to low-latitude regions, while they increase the equatorial electrojet current leading to dBdt perturbations in dayside equatorial regions. We investigate the effects of shock impact angles and speeds on the subsequent dBdt perturbations with a database of 547 shocks observed at the L1 point. By adopting the threshold of dBdt = 100 nT/min, identified as a risk factor to power systems, we find that dBdt 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 dBdt > 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 dBdt perturbations. We suggest that these results may provide insights for GIC forecasting aiming at preventing degradation of power systems due to GICs