Modeling Geoelectric Fields in Ireland and the UK for Space Weather Applications

Abstract

Geoelectric fields at the Earth's surface caused by geomagnetic storms have the potential to disrupt and damage ground‐based infrastructure such as electrical power distribution networks, pipelines, and railways. Here we model geoelectric fields in Ireland and the UK during both quiet and active time intervals of geomagnetic conditions using measurements from magnetic observatories and electromagnetic tensor relationships. The analysis focused on (1) defining periods of the magnetic field variations that are largely affected by the geomagnetic storms, between 30 and 30,000 s; (2) constraining the electromagnetic tensor relationships that defines the Earth's response to magnetic field variations; (3) implementing and validating two approaches for modeling geoelectric fields based on measurements from magnetic observatories and local and interstation electromagnetic transfer functions; and (4) estimating uncertainties when modeling geoelectric fields. The use of interstation tensor relationships allowed us to differentiate between regional and local geomagnetic sources. We found coherence values of 0.5–0.95, signal‐to‐noise ratio of 1–15 dB, normalized root‐mean‐square values of 0.8–3.4, and root‐mean‐square values of 0.7–84 mV/km. Within these ranges of values, sites in close proximity (<100 km) to a magnetic observatory and not affected by local storms will provide the most accurate results, while sites located at further distances and affected by spatially localized features of the storm will be less accurate. These methods enable us to more accurately model geomagnetically induced currents, and their associated uncertainties, in the British and Irish power networks.

Exploring the Influence of Lateral Conductivity Contrasts on the Storm Time Behavior of the Ground Electric Field in the Eastern United States

“…Calculations are performed using the APPL 3‐D conductivity model. 3‐D MT intersite impedances (Campanya et al, ; Hermance & Thayer, ; Kruglyakov & Kuvshinov, ) that relate the surface horizontal electric field at each grid point with the surface horizontal magnetic field at a fixed base site are then calculated for each FFT frequency . In this model study coincides with location of FRD observatory. Time‐varying horizontal magnetic field at the location of the FRD which was calculated earlier via 3‐D EM forward modeling using the MHD source and the APPL model is Fourier transformed to obtain .…”

The Role of Global/Regional Earth Conductivity Models in Natural Geomagnetic Hazard Mitigation

“…The second step toward obtaining GIC estimates in a power grid requires geophysical knowledge and involves estimation of geoelectric fields at the Earth's surface. Specifically, the Earth impedances may be obtained through construction of a 1D (e.g., Ádám et al 2012;Fernberg 2012) or 3D (e.g., Kelbert et al 2019) Earth conductivity model, or, alternatively, empirical 3D Earth impedances and interstation transfer functions may be used (e.g., Bonner and Schultz 2017;Campanyà et al 2019). These different options for choosing the Earth impedances are further discussed in Sect.…”

“…Ground-level geoelectric fields could be used as the input to power grid flow models, both operationally, for situational awareness in the control room, as well as for historical scenario analysis that allows a power grid to investigate potential points of failure in their grid in advance of a space weather event. The use of 3D MT transfer functions as part of the workflow has been shown to provide an improvement in ground-level geoelectric fields relative to the use of 1D conductivity models (e.g., Weigel 2017; Bonner and Schultz 2017; Kelbert et al 2017;Campanyà et al 2019). We suggest that interpolation based on a numerical solution of Maxwell's equations using a 3D conductivity model such as that of the contiguous USA (CONUS; Kelbert et al 2019) could provide a further improvement against the utilization of empirical MT transfer functions interpolated to the locations of interest.…”

“…These developments have enabled derivation of fully 3D electrical conductivity models that are now becoming available for geomagnetic hazard applications. In fact, while the plane-wave Starting with the empirical geomagnetic and magnetotelluric data (green), one could either use interpolation methods to estimate real-time gridded geoelectric fields ("data-space workflow," shown in blue; e.g., Bonner and Schultz 2017;Campanyà et al 2019), or a conductivity model could be used for a physics-based variant of the interpolation ("model-space workflow," shown in red, e.g., Marshall et al 2019). Method 1: interpolation using multi-station transfer functions; not based on physics.…”

“…Earth's electrical conductivity was beyond the scope of this study. Most recently, a novel geoelectric field modeling approach based on local and interstation transfer functions was developed and validated in Ireland and the UK by Campanyà et al (2019).…”