by Charles Rotter at wattsupwiththat.com
An analysis is made of geophysical records of the 24 March 1940, magnetic storm and related reports of interference on long-line communication and power systems across the contiguous United States and, to a lesser extent, Canada. Most long-line system interference occurred during local daytime, after the second of two storm sudden commencements and during the early part of the storm’s main phase. The high degree of system interference experienced during this storm is inferred to have been due to unusually large-amplitude and unusually rapid geomagnetic field variation, possibly driven by interacting interplanetary coronal-mass ejections. Geomagnetic field variation, in turn, induced geoelectric fields in the electrically conducting solid Earth, establishing large potential differences (voltages) between grounding points at communication depots and transformer substations connected by long transmission lines. It is shown that March 1940 storm-time communication- and power-system interference was primarily experienced over regions of high electromagnetic surface impedance, mainly in the upper Midwest and eastern United States. Potential differences measured on several grounded long lines during the storm exceeded 1-min resolution voltages that would have been induced by the March 1989 storm. In some places, voltages exceeded American electric-power-industry benchmarks. It is concluded that the March 1940 magnetic storm was unusually effective at inducing geoelectric fields. Although modern communication systems are now much less dependent on long electrically conducting transmission lines, modern electric-power-transmission systems are more dependent on such lines, and they, thus, might experience interference with the future occurrence of a storm as effective as that of March 1940.
- Extreme geomagnetic field variation realized during the March 1940 storm might have resulted from the interaction of ICMEs
- Long-line interference in the U.S. occurred during local daytime and in the upper Midwest and East, where surface impedance is high
- Voltages measured on grounded long lines during the storm exceeded 1-min voltages that would have been induced by the March 1989 storm
Plain Language Summary
On 24 March 1940, a pair of concentrated, and possibly interacting, bursts of solar wind forced an intense magnetic storm on Earth. Geomagnetic field variation during the storm induced high-amplitude geoelectric fields in the solid Earth’s conducting interior. These geoelectric fields drove uncontrolled currents in grounded long-wire communication- and electricity-power-transmission systems in the United States and Canada, causing significant operational interference in those systems. This interference was primarily experienced in the upper Midwest and the eastern United States, and many incidents of interference were reported in the popular press. Voltages monitored on several lines were greater than studies estimate would have occurred during the great storm of March 1989. In terms of its impact on communication and power systems, the March 1940 magnetic storm was one of the most significant ever experienced by the United States. Modern communication systems are less dependent on long electrically conducting transmission lines. On the other hand, modern electric-power-transmission systems are more dependent on such lines, and they, thus, might experience interference with the future occurrence of a storm like that of March 1940.
The front page of the New York Times (1940a) declared that, on 24 March 1940, something akin to a “sun-spot tornado” had disrupted long-line communication transmission systems. The Washington Post said that an “invisible sun-spot storm” had interfered with radio, telephone, and telegraph communication systems across “half the world,” including trans-Atlantic communication systems (Smith, 1940). The headline of the Boston Daily Globe (1940) used more modern terminology, announcing that the United States had been hit by a “magnetic storm.” As a result of the storm, numerous protective breakers had to be replaced on American communication systems (Germaine, 1940; Ireland, 1940). In other parts of the world, interference was reported on telegraph systems, for example, in Australia (e.g., Morning Herald, 1940), in Great Britain (e.g., Daily Telegraph, 1940), and in India (e.g., Rangaswami & Basu, 1940). Interference was also reported by electricity utility companies, including alternating current waveform “distortion,” “reactive power,” “tripping out” of transformers, and “blown transformer fuses” (Davidson, 1940). John A. Fleming, then Director of the Department of Terrestrial Magnetism, Carnegie Institution of Washington, noted the quality that distinguished the March 1940 storm was the “unusual violence” of its geomagnetic “fluctuation” (Fleming, 1940, his p. 476, 480). These qualities, in his opinion, likely meant that the March 1940 storm was “the greatest magnetic disturbance which has ever been recorded” up to that point in time (Fleming, 1940, his p. 480). Harold W. Newton of Greenwich Observatory offered a slightly more qualified summary, describing the March 1940 storm as “remarkable for its agitation” and “one of the big storms of (the) century” (Newton, 1940, his p. 130).read more