Nowcasting and Validating Earth's Electric Field Response to Extreme Space Weather Events Using Magnetotelluric Data: Application to the September 2017 Geomagnetic Storm and Comparison to Observed and Modeled Fields in Scotland

In the United Kingdom, geomagnetically induced currents (GICs) are calculated from thin-sheet electrical conductivity models. absence of models, time derivatives magnetic fields sometimes used as proxies for GIC-related electric fields. An alternative approach, favored in States, is to calculate storm time-independent impedance tensors computed an array magnetotelluric (MT) sites and recorded at geomagnetic observatories or assumed line current A paucity direct measurements has restricted validation these different techniques nowcasting GICs. Here, we present unique field data seven MT Scotland that before, during, after September 2017 storm. By Fourier transforming spectra using back domain, able make comparisons with measured series. This enables us test validity approaches Our preferred technique involves frequency domain multiplication a regional site local tensor been corrected horizontal gradients between perturbation derived depth sounding (GDS). Scatter plots scaling factors nowcasted demonstrate importance coupling polarization source Earth's direction-dependent deep structure.