Comparison of the modelled geoelectric fields of the Carrington and Halloween storms

An extreme geomagnetic storm comparable to the Carrington event in 1859 could have a significant impact on modern infrastructure, such as power grids. A previously published simulation by Blake et al. (2021, Space Weather, https://doi.org/10.1029/2020SW002585) reconstructed the magnetic field observations at Colaba, India, during the Carrington storm and provided estimates of the magnetic field variations around the world. We use these results as an input to a first-principle modelling method to estimate the geoelectric field in Fennoscandia based on a 3-dimensional ground conductivity model. We compare the results with the Oct 2003 Halloween storm, which is one of the strongest events in the past 100 years, and of which spatially dense magnetometer recordings are available in Northern Europe. Comparison of the maximum modelled geoelectric field values in Fennoscandia indicates that a Carrington-class storm could generate electric fields 1.4–20.4 times larger than the Halloween storm did, with the Carrington to Halloween ratio having a mean of 6.7 and standard deviation of 2.7