Identifying GIC-effective geoelectric hazard scenarios in the German power grid

Kurzfassung

In previous work, we applied our modelling framework for geomagnetically induced currents (GICs) in the German high-voltage transmission grid to geomagnetic storms of Solar Cycle 25, including the May 2024 event. This analysis revealed significant GIC amplitudes (>20 A) across several substations. This consequently raises the question of the likelihood of such an impact in the future and the relevant local indicators. An established approach in the space weather community is the derivation of so-called geoelectric hazard maps from a purely geophysical perspective. This typically involves a selection of historical events, usually based on geomagnetic disturbance peaks recorded by geomagnetic observatories, and a statistical evaluation of the corresponding induced geoelectric fields, calculated considering the local conductivity structure. Here we present the first results of this approach and address its adaptation to the technical characteristics of the German transmission grid. Based on assumed GIC thresholds and induced voltages in the transmission lines, respectively, we identify GIC-effective geoelectric field scenarios. To further enhance the practical relevance, we discuss the extent to which these scenarios are recognizable in readily available measurements or derived products, e.g. geomagnetic indices, which could serve as local GIC indicators.