Magnetic-storm geoelectric hazard maps and the induction of voltages on power-grids

A summary is presented of recent U.S. Geological Survey (USGS) Geomagnetism Program research undertaken in support of priorities established by National Space Weather Action Plan of the National Science and Technology Council’s Space Weather Operations, Response, and Mitigation (SWORM) Working Group. Analysis is made of geoelectric fields that are induced in the Earth’s electrically conducting interior during intense magnetic storms and their representation as maps and as voltages induced on electric-power grid networks. Estimates of geoelectric fields are obtained by convolution of geomagnetic time series (such as those provided by USGS observatories) with Earth-surface impedance tensors (such as those obtained by the EarthScope project of the National Science Foundation). Statistical analysis of long geoelectric amplitude time series gives estimates of extreme-values, such as those realized during rare but intense magnetic storms. Time-dependent maps of geoelectric vectors are constructed for individual magnetic storms, and voltages on power-grid lines are estimated by integrating the geoelectric vectors along the length of the transmission lines. Results inform studies of resilience of power-grid networks to geomagnetic disturbance as mandated by the Federal Energy Regulatory Commission (FERC), which is now being undertaken by utility companies within the North American Electric Reliability Corporation (NERC). Results also highlight the practical importance of both long-term geomagnetic monitoring and continental-scale magnetotelluric surveys.