Influence of ground conductivity models on GIC hazard estimation in Germany

Kurzfassung

The hazard posed by Geomagnetically Induced Currents (GICs) to the regular operation of grounded infrastructure originates from the induced geoelectric field (GEF) under geomagnetically disturbed conditions. In order to specify the GIC hazard in Germany we model the GEF from the horizontal geomagnetic disturbance field in combination with surface impedance tensors under the plane wave assumption. The former is obtained byfitting Spherical Elementary Current Systems basis functions to magnetic field measurements from INTERMAGNET observatories while the latter are extracted from a predefined conductivity model. Here, we focus on a comparison of GEF results obtained using two different conductivity models covering Germany. Those are "EURHOM", a 1D model well-known in the European GIC community, and our new dedicated 3D model "EUSigma". The new model is not only better resolved but also includes realistic conductivity variations due to the ocean/sea and marine sediments, which are known to affect impedance tensors at GIC-relevant frequencies near coastlines. We calculate GICs exemplarily at selected substations and geomagnetic disturbance events and discuss options to judge the plausibility of the results. All in all our study helps to identify the level of complexity needed in the GEF modeling in order to derive meaningful GIC hazard maps for Germany down the line.