Geoelectric field estimation and power-line integration using a 3D electrical conductivity model of the United States

Estimation of ground-level geoelectric fields has been identified by the electrical power industry as a key capability in assessment and mitigation of the impacts of space weather on electrical power infrastructure. One approach to estimation of ground-level geoelectric fields in the United States is to employ the best available three-dimensional Earth conductivity models (Meqbel et al., 2014; Yang et al., 2015; Murphy & Egbert, 2017 and others). These models are the results of regional magnetotelluric inversions based on NSF's Earthscope USArray impedances (Schultz et al., 2006-2018). The work on the 3D conductivity models is ongoing as new USArray data are obtained, and new methods for improved magnetotelluric inversion are developed. Here, we describe the initial USGS compilation of 3D electrical conductivity models for the United States. We analyze the high-resolution gridded Earth impedances obtained in selected regions of the United States, and discuss the effects of impedance grid resolution on the electric fields integrated along power lines, which serve as a proxy for geomagnetically induced current (GIC) amplitude. Our approach also allows us to analyze the effects of magnetotelluric distortion due to the small-scale near-surface anomalies on the GIC proxy. This analysis feeds into the development of operational Geoelectric Field Maps at NOAA's Space Weather Prediction Center (SWPC), a system for near real-time (no more than a several mins data latency) estimation of spatially variable ground-level geoelectric fields. A preliminary experimental capability is now available to the public at SWPC's website (http://www.swpc.noaa.gov). The deployment of these maps represents a significant advance in the specification of space weather hazards compared to what was previously available, i.e. global geomagnetic indices, providing the electrical power industry with a tool to assess regional space weather hazards in near real-time. An emphasis will also be made to identify key priorities needed for future improvements of this product. We encourage the community to make use of these operational tools to assist us in cross-comparison and validation.