On the spatial complexity of geoelectric fields induced during magnetic storms in realistic lithospheric conductivity

In support of a US Geological Survey priority to pursue natural hazard science and a National Science and Technology Council project for Space Weather Operations, Response, and Mitigation, we report on an analysis of the feasibility of mapping surficial geoelectric fields that are induced in the Earth's electrically conducting interior during magnetic storms and which represent a hazard for the operation of electric-power grids. The most difficult challenge for geoelectric mapping is related to the three-dimensional structural complexity of the solid Earth – interior electrical conductivity spans many orders of magnitude and it is distributed across a wide range of spatial scales. To investigate the effect of realistic conductivity structure on storm-time geoelectric induction, we perform a synthetic analysis using impedance tensors obtained from an NSF EarthScope magnetotelluric survey at sites distributed with nominal 70-km spacing across the midwestern United States. With these tensors, we perform a synthetic analysis -- calculating geoelectric variation induced by a geomagnetic field that is spatially uniform, varying sinusoidally in the north-south direction and in time with a period that is characteristic of magnetic storm variation. The geoelectric vectors show substantial geographically distributed differences in polarization (with differences between some preferred inductional directions approaching 90 degrees) and magnitude (at least 2 orders of magnitude). This work highlights the need for a complete magnetotelluric survey of the United States, modeling of lithospheric and deep Earth conductivity, continuous geoelectric monitoring at selected sites across the United States, regional assessment of geoelectric hazards, and the development of algorithms for time-domain estimation of geoelectric induction.