Geomagnetically induced currents (GICs) have been the bane of technology-dependent societies. In telegraph lines, submarine cables, railroads and electrical power grids, nature has found a way to insert its highly variable self, via GICs, into the workings of modern systems often with little advance warning.

The highest concern for GICs is presently associated with regional high-voltage power grids, some of which cross national borders.

One hundred years ago T. R. Taltavall, editor of the technical periodical Telegraph Telephone Age, declared, “Earth currents are arch enemies of the telegraph and submarine cables”. He made this declaration about the GIC effects of a geomagnetic storm that had interfered with telegraph services across much of the world on 17 June 1915. Editor Taltavall was convinced this was a serious problem that needed both engineering and scientific solutions and was willing to so proclaim. The “archenemy” of long Earth cabled systems is still with us and is further able to invade our interconnected, long-distance power grids. Engineering and scientific solutions are still needed.

Eruptions from the Sun’s atmosphere produce outward propagating, transient bubbles of magnetized gas, called coronal mass ejections (CMEs). At, and near, the maximum of the sunspot cycle the frequency of these ejecta increases. Fast-moving CMEs passing Earth can impulsively deform Earth’s protective magnetic field, causing enhanced electromagnetic fields that span high and low latitudes. The electric part of the field is known as the geoelectric field. Geoelectric field variations couple into closed-loop transmission systems and grounded cables and conductors, causing (1) fluctuating GICs in communication and power transmission lines, (2) voltage swings, transformer heating, and reactive power loss in high-voltage power transmission systems, and (3) damage in power transformers and possible enhanced corrosion in pipelines. The highest concern for GICs is presently associated with regional high-voltage power grids, some of which cross national borders. Just last week the administration issued a national strategy and action plan to prepare and respond to space weather events.

Unlike hurricanes and ice storms, which (1) get plenty meteorological press, (2) are usually regional in effect, and (3) are forecastable 2–3 days in advance, GIC events may span continents and can develop in a matter of minutes after their progenitor disturbances are detected 15–60 minutes upstream from Earth in the solar wind. Although visual indications of CMEs are available hours to days in advance of geodisturbances, only a fraction of the eruptions pose a GIC threat, but which fraction is an active area of research. To add further complication, these infrequent, but potentially high impact, events are discussed in the parlance of electromagnetic and engineering terms that cause the proverbial public eye to glaze over.

Although the problems of space weather and complex power system responses are intellectually challenging decision makers need to be informed even if they do not come from a scientific background. Bright students, who are the future scientists and engineers of society, should also be aware of the grand challenges at this interface of science and engineering.

To help address these concerns, the Space Weather editors and a group of guest commentators reviewed the holdings of AGU journals and identified the highlights, gaps, and policy implications of GICs from their perspectives. Trevor Gaunt provides an overview of the collection and Antti Pulkkinen addresses the state of GIC modeling and forecasting. Finally, Seth Jonas and Eoin McCarron provide a policy perspective. This collection of 100+ articles is a “living collection”. Relevant cutting edge papers will be included as they are published.

—Delores J. Knipp, Editor in Chief, Space Weather and Space Weather Quarterly; email:


Knipp, D. J. (2015), GICs: The bane of technology-dependent societies, Eos, 96, Published on 16 November 2015.

Text © 2015. The authors. CC BY-NC-ND 3.0
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