Regional geomagnetic disturbances in Fennoscandia: statistical observations, modelling, and driving mechanisms

Geomagnetically Induced Currents (GICs) are a space weather hazard that can negatively impact large ground-based infrastructures such as power lines, pipelines, and railways. They are driven by the dynamic spatiotemporal behaviour of currents flowing in the ionosphere, which drive rapid geomagnetic disturbances on the ground. Since the earth is intrinsically conductive, telluric currents are induced, setting up a geoelectric field that can drive currents in man-made systems. Recent studies have highlighted the highly-localised nature of these disturbances and that the source mechanisms are unclear; as a result, their prediction poses a significant challenge. In this work we report on the localised nature of these disturbances over Fennoscandia, the role of global MHD model resolution in capturing these events, possible source mechanisms, and how these are key to accurate GIC modelling. We show that dB/dt can vary by several times over just hundreds of kilometres and that this variation can result in up to 60% difference in GICs across a 200 km transmission line. Using different resolutions of the Space Weather Modelling Framework (SWMF), our results indicate that when modelling GICs, the higher resolution performs better when considering the ability to exceed pre-defined thresholds. Using decades of IMAGE magnetometer measurements, we relate highly localised disturbances to possible source processes such as substorms. The implications from our work are that: 1) in such cases, the localised nature of geomagnetic disturbances should be considered in the GIC modelling process, 2) telluric contributions to dB/dt can be significant, 3) higher resolution runs than those typically used in operational settings are better suited to modelling GICs, 4) substorms continue to hinder GIC modelling at high latitudes both from a global MHD modelling standpoint and the ability to account for their localised nature measured on the ground. Advancement in the above areas will be key to achieving more localised predictions and improved geoelectric field forecasts.