Joint Analysis With Swarm and Ground Stations: Ionospheric Current System and Geomagnetically Induced Currents

Sudden changes in the ground magnetic field, driven by geomagnetic activity, can ultimately generate geomagnetically induced currents (GICs), which can have a significant impact on artificial technology systems. High rates of change in the horizontal geomagnetic field (dH/dt) can be used as a substitute for the strength of GICs. It has been suggested that GIC signals in the nightside local time sectors can indirectly be driven by field-aligned currents (FACs) flowing into the ionosphere, which themselves can be generated during arrival of bursty bulk flows (BBFs) into the nightside transition region (through an improved substorm current wedge, SCW). We extend the analysis of the 7 January 2015 substorm by utilizing multi-point observation techniques from ground stations and satellites. We combine the data from the magnetosphere and ionosphere with the behavior of the dH/dt component obtained from ground stations. Our results confirm that Region 1 (R1) type FACs driven by the BBF arrivals form a loop with the westward auroral electrojet currents (AEJs), an important driving factor for ground GICs. We also briefly show the role of corresponding ultra-low frequency (ULF) waves during the event. This further explains how BBFs affect ground GICs, which will help to understand the coupling between ionospheric current systems and ground currents.