Analysis of the geoelectric field in Sweden over solar cycles 23 and 24: spatial and temporal variability during strong GICs events

Extreme space weather events can produce geomagnetically induced currents (GICs) that flow along long conductor systems such as power grids and pipelines. GICs can interrupt the operation of these systems by damaging transformers and increasing the rate of pipeline corrosion. GICs depend on the enhancement of the geoelectric field, where the magnitude, geographic location, and occurrence depend on the solar wind-magnetospheric-ionospheric coupling processes and the ground conductivity. Thus, countries at high latitudes are potentially more vulnerable to GICs due to higher geomagnetic activity.

Magnetic field measurements (e.g. dB/dt) have been used for a long time as a proxy for GICs with some success. However, studying the behaviour of the geoelectric field is required to fully understand the GIC response during extreme space weather events. In this study, the geoelectric field was computed using data from the IMAGE network and a 1D conductivity model (SMAP) across Sweden. A 19-year statistical analysis of the daily maximum magnitude of the geoelectric field (E) has been performed for solar cycles 23 and 24. We examine the temporal and spatial distribution of the geoelectric field in Sweden to determine the importance of including the ground conductivity when assessing the strongest events and their implications to GICs.

 We found that the daily maximum E is more frequently registered in the dusk sector related to the eastward convection electrojet and a second relative maximum is observed in the dawn sector related to westward convection electrojet. The stronger E values are related to well-known extreme space weather events. However, these events produce different responses at different latitudes due to the changes in ground conductivity and ionospheric response. Therefore, the strongest geoelectric fields at different geographical locations are not all driven by the same events.