The Geomagnetic Storm on 10–12 May 2024 and Its Effect on the Swedish Power Grid

On 10–12 May 2024, at least five interplanetary coronal mass ejections (ICMEs) arrived at Earth and caused the strongest geomagnetic storm in over 20 years. During this geomagnetic storm, a disturbance occurred in a transformer in southern Sweden, causing a drop in power supply in the power line connecting Sweden and Poland. The power grid operator confirm geomagnetically induced currents (GICs) were the cause. The purpose of this study is to investigate the circumstances around and the cause of this disturbance, as well as analyzing if the effect in southern Sweden could have been different had the first ICME arrived earlier or later. Using satellite data, ground magnetometer measurements and a ground conductivity model over Fennoscandia, we perform this analysis from the solar wind down to the induced geoelectric field. Further, we compare this event to two previous disturbances in the same power line caused by GICs. The results of this study show that the disturbance occurred at a time of turbulent solar wind conditions and the merging of two ionospheric current structures. However, the disturbance did not occur at the time of peak induced geoelectric field throughout the storm, at the location of the disturbance. From the timing analysis, we see that most magnetic local time sectors along the same geomagnetic latitude, experienced similar magnitudes of geoelectric field as a result of the storm. The results suggest that there is a high probability the disturbance would have occurred even if the ICME would have arrived at a different time.