A Statistical Study of Possible Drivers for Substorm dB/dt Spikiness

Variations in the ionospheric currents can cause rapid disturbances in the magnetic field at the ground level, so called dB/dt spikes, and Geomagnetically Induced Currents (GICs) that can harm human infrastructure. When investigating dB/dt spike occurrence and GIC risks, the focus has typically been on geomagnetic storms. However, recently it has been argued that it is the substorm phenomena which contains the crucial physics for spikes and GICs, and which instead should be in focus. Here we present results from a statistical investigation on the occurrence of spikes in substorms (“substorm spikiness”) as observed in the geomagnetic activity indices SME, SMU, and SML provided by the SuperMAG collaboration. We study the substorm spikiness for different years in the solar cycle and for different levels of geomagnetic disturbance according to the SMR ring current index, and we search for possible solar wind drivers. We investigate both the magnitude and the variability of various potential drivers and conclude that some of the more important drivers are the solar wind speed magnitude and its variability.