Geolectric field measurement, modelling and validation during geomagnetic storms in the UK

Significant geoelectric fields are produced by the interaction of rapidly varying magnetic with conductive Earth, particularly during intense geomagnetic activity. Though usually harmless, large or sustained can damage grounded infrastructure such as high-voltage transformers and pipelines via geomagnetically induced currents (GICs). A key aspect understanding effects space weather on is through spatial temporal variation field. Globally, there few long-term monitoring sites field, so in 2012 measurements horizontal surface field were started at Lerwick, Eskdalemuir Hartland observatories UK. Between 2020, maximum value observed was around 1 V/km 0.5 0.1 March 2015 storm. These observations also allow comparisons models to be made. We use compute magnetotelluric impedance transfer functions each observatory for periods from 20 30,000 s. then used predict selected storm times that match recorded very well (correlation 0.9). values a thin-sheet model Britain, accounting diverse geological bathymetric island setting. find captures peak phase band-passed reasonably well, linear correlation 0.4 general. From these two modelling approaches, we generate historic storms (March 1989 October 2003) estimates past up 1.75 Eskdalemuir. However, evidence high voltage transformer GIC suggests likely represent an underestimate true value.