Geomagnetically induced currents caused by interplanetary shocks with different impact angles and speeds

Abstract

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 mid‐ to low‐latitude regions, while they increase the equatorial electrojet (EEJ) 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 9 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 EEJ 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.

Plain Language Summary: The occurrence of geomagnetically induced currents (GICs) poses serious threats to modern technological infrastructure. GIC effects are usually known to be elevated during geomagnetic storms in regions of high latitudes. However, there has recently been some attention to GIC effects in equatorial regions given a high number of power grids arising in those regions. Such stations may be located right beneath a strong electric current flowing in the dayside ionosphere, named the equatorial electrojet current. In this paper, we study the effects of shock waves driven by solar disturbances on the Earth's magnetic field and the subsequent generation of GICs on the ground. We associate, for the first time, shock impact angles and speeds with the subsequent GIC generation. We find that stations located beneath the equatorial electrojet current are subject to high‐risk GIC intensifications if high‐speed and nearly frontal shocks strike the Earth when the station is located around noon local time. We then suggest that power plant operators use real‐time existing shock forecasting services to take actions in a time window of 30‐60 minutes when a shock with high speed and small impact angle is detected around 1 million kilometers from Earth toward the Sun.