The March 1940 Superstorm: Geoelectromagnetic Hazards and Impacts on American Communication and Power Systems

An analysis is made of geophysical records the 24 March 1940, magnetic storm and related reports interference on long-line communication power systems across contiguous United States and, to a lesser extent, Canada. Most system occurred during local daytime, after second two sudden commencements early part storm's main phase. The high degree experienced this inferred have been due unusually large-amplitude rapid geomagnetic field variation, possibly driven by interacting interplanetary coronal-mass ejections. Geomagnetic in turn, induced geoelectric fields electrically conducting solid Earth, establishing large potential differences (voltages) between grounding points at depots transformer substations connected long transmission lines. It shown that 1940 storm-time communication- power-system was primarily over regions electromagnetic surface impedance, mainly upper Midwest eastern States. Potential measured several grounded lines exceeded 1-min resolution voltages would 1989 storm. In some places, American electric-power-industry benchmarks. concluded effective inducing fields. Although modern are now much less dependent lines, electric-power-transmission more such they, thus, might experience with future occurrence as 1940.