DOWN TO EARTH WITH AN ELECTRIC HAZARD FROM SPACE

Electric fields induced in the Earth during magnetic storms can drive uncontrolled currents in communication and electric-power systems and interfere with their operation. In the United States, significant system interference was experienced during great storms in March 1940, August 1972, and March 1989, and during several earlier storms. A communication or power system's vulnerability to geoelectric hazards depends on its topology, interconnection, and grounding. The geoelectric hazard depends on the time-dependent geography of storm-time geomagnetic disturbance and the frequency-dependent geography of surface impedance, which, itself, is a function of the Earth's subsurface electrical conductivity structure. We develop maps of the hazards and impacts of the March 1989 storm, which caused a blackout in Québec, Canada, and brought significant interference to power systems in the Mid-Atlantic and Northeast United States. Results are based on modeling geomagnetic monitoring data, geoelectromagnetic survey data, and a compilation of published reports of power-system interference. In the United States, during the storm, electric-power system interference was concentrated where the lithosphere is relatively electrically resistive, and when and where the geoelectric field was of high amplitude. This was particularly true in the Mid-Atlantic and Northeast, near many of America's largest cities, and in the upper Midwest. Retrospective analyses, such as ours for the March 1989 storm, show where utility companies might concentrate their efforts to mitigate the impacts of future, even more intense, magnetic superstorms.