Estimating geoelectric fields for geoelectric hazard assessment: an examination of data and models within complex physiographic zones

Abstract

During magnetic storms, time-varying geomagnetic fields induce geoelectric fields at the surface that produce geomagnetically induced currents (GICs) within power transmission systems. These GICs can permanently damage these systems, thus motivating research to understand how geoelectric fields behave during storm events. Geomagnetic field data obtained through the INTERMAGNET program are convolved with EarthScope USArray magnetotelluric impedances and impedances collected by Helmholtz Centre for Ocean Research Kiel (GEOMAR), FU Berlin, and GFZ Potsdam to estimate geoelectric variations during a magnetic storm. I consider a magnetic storm ranking G4 occurring between 22 June 2016 to 26 June 2016 recorded at the Brandon, Manitoba (BRD), Fredericksburg, Virginia (FRD), and San Juan (SJG) magnetic observatories. From this, I produce estimated geoelectric fields throughout the duration of a magnetic storm and examine these geoelectric fields across short geographic distances and within the same physiographic zone. This study shows that the geoelectric response of two sites within 200 km of one another can differ by up to two orders of magnitude (4484 mV/km at one site and 41 mV/km at another site 125 km away). I also examine how these geoelectric fields vary across a coastline in order to examine the geomagnetic coast effect's influence on geoelectric hazard assessment. From this, I demonstrate that the application of uniform 1 dimensional conductivity models of the subsurface to wide geographic regions is insuffcient to predict the geoelectric hazard at a given site. This necessitates that an evaluation of the 3-dimensional conductivity distribution at a given location is necessary to produce a reliable estimation of how the geoelectric field evolves over the course of a magnetic storm.