Speaker
Description
We examine the geoelectric field and geomagnetically induced currents (GICs) during the May 2024 superstorm using a novel method. The divergence-free part of the geoelectric field (EDF), associated with rapid magnetic field variations, is estimated from ground-based magnetic field observations using spherical elementary current systems. The curl-free part of the geoelectric field (ECF), associated with charge accumulation, is estimated from EDF using coefficients that linearly relate ECF to EDF in the time domain. We apply the method to both regional 10-s IMAGE magnetometer observations and global 1-min SuperMAG observations. We compare the resulting GICs in the Finnish benchmark power grid and conclude that, in the absence of ground conductivity information and higher cadence data, EDF estimated from 1-min magnetic field observations alone can provide a reasonable proxy for GIC activity in a power grid. However, some substations are strongly affected by local ground conductivity gradient structures and the GICs at such substations may be poorly described by EDF. Comparison of the various contributions in driving GICs reveals combinations of the local ground conductivity distribution and the power grid structure that can result in particularly intense GICs at certain substations for certain external drivers.
