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 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.

Interhemispheric Asymmetries in the Ground Magnetic Response to Interplanetary Shocks: The Role of Shock Impact Angle

“…Finally, we note from Figure that at many latitudes, particularly in the Southern Hemisphere, the frontal shock (bottom panel) generates comparable or more intense than the inclined shock (upper panel); this is consistent with the results of Oliveira et al (). However, this pattern does not hold at all latitudes; in particular, the inclined shock generates magnetic perturbations with significantly larger intensities than the frontal shock at many latitudes in the Northern Hemisphere.…”

“…We used a recently published database of shock impact angles from Oliveira et al (), along with a recently deployed chain of magnetically conjugate ground magnetometers to test hypotheses motivated by the simulations of Oliveira and Raeder (), namely the hemisphere that the IP shock strikes first has (i) the first ground magnetic response and (ii) the most intense response. We find that the hemisphere the shock strikes first generally has the first response in and the most intense, though other factors such as the local time dependence of the M‐I current systems excited by the shock and the ionosphere conductivity play important roles.…”

Satellite Orbital Drag During Magnetic Storms

“…The first dashed vertical line indicates the time of CME/shock impact (leading edge), whereas the second one represents the time in which IMF B z abruptly turns southward (magnetic material). The first event is associated with the sudden impulse whose well‐known signature is a sharp increase in ground magnetic measurements (Oliveira et al., ; Rudd et al., ), while the second event usually coincides with the storm main phase onset, when Dst/SYM‐H measurements become highly depressed due to ring current energization (Gonzalez & Tsurutani, ; Gonzalez et al., ). Although compressions resulting from dynamic pressure enhancements can increase high‐latitude neutral density measurements (Ozturk et al., ; Shi et al., ), storm time heating is responsible for larger and global effects on the thermospheric neutral mass density (e.g., Krauss et al., ; Oliveira et al., ).…”

Effects of Nearly Frontal and Highly Inclined Interplanetary Shocks on High‐Latitude Field‐Aligned Currents (FACs)

“…Here θxn ranges from 0° to 180° where θxn = 180° is associated with a purely frontal shock, while the smaller θxn , the more inclined the shock. The shock list provided by Oliveira et al () is used in this study to identify NFS and HIS events. The list provides the shock arrival time as the positive jump in sudden impulse onset, shock impact angle, shock speed, and the maximum worldwide horizontal component of the ground magnetometer dB/dt measurements.…”

“…We provide a statistical analysis of the response of high‐latitude FACs to the impact of nearly frontal shocks (NFSs) and highly inclined shocks (HISs). We select 49 NFS events and 49 HIS events between October 2009 and September 2017 from the shock list provided by Oliveira et al () where the zero‐epoch time is the shock/compression onset time. Derived FAC distributions and total currents during the hour before and after the zero‐epoch time are determined and used in superposed epoch analysis.…”