Rosenqvist and Hall (2019), https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018SW002084 developed a proof-of-concept modeling capability that incorporates a detailed 3D structure of Earth's electrical conductivity in a geomagnetically induced current estimation procedure (GIC-SMAP). The model was verified based on GIC measurements in northern Sweden. The study showed that southern Sweden is exposed to stronger electric fields due to a combined effect of low crustal conductivity and the influence of the surrounding coast. This study aims at further verifying the model in this region. GIC measurements on a power line at the west coast of southern Sweden are utilized. The location of the transmission line was selected to include coast effects at the ocean-land interface to investigate the importance of using 3D induction modeling methods. The model is used to quantify the hazard of severe GICs in this particular transmission line by using historic recordings of strong geomagnetic disturbances. To quantify a worst-case scenario GICs are calculated from modeled magnetic disturbances by the Space Weather Modeling Framework based on estimates for an idealized extreme interplanetary coronal mass ejection. The observed and estimated GIC based on the 3D GIC-SMAP procedure in the transmission line in southern Sweden are in good agreement. In contrast, 1D methods underestimate GICs by about 50%. The estimated GICs in the studied transmission line exceed 100 A for one of 14 historical geomagnetic storm intervals. The peak GIC during the sudden impulse phase of a “perfect” storm exceeds 300 A but depends on the locality of the station as the interplanetary magnetic cloud hits Earth.

A dangerous consequence of extreme solar flares is a serious and prolonged disruption in the electricity supply. Society is now extremely dependent on electricity, so this raises numerous issues ranging from societal security to large economical losses. To avoid this, it is important to understand how strong the ground-induced currents (GICs) that arise as a consequence of the solar eruption can be, and which areas are vulnerable. GICs depend on how large and quickly the geomagnetic field at ground level changes and also the properties of the ground underneath. This study use a full 3D model to investigate the importance of lateral conductivity gradients at for example, coastal areas, on the severity of GICs in Sweden. The model is validated against a tailored field trial on a transmission line in a coastal area. Historical recordings of major storms is applied to the model in order to investigate how strong GICs can be expected in this particular transmission line. To understand a worst-case scenario, an ideal extreme solar storm and the simulated impacts in Sweden have been investigated.