Geomagnetically Induced Currents

Thumbnails of regional conductivity graphs. (Fernberg et al. 2013, in prep.)

Geomagnetically-induced currents (GICs) flowing along electric power-transmission systems and other electrically-conducting infrastructure are produced by a naturally induced geo-electric field during geomagnetic disturbances. An extreme example of this type of occurrence was the great magnetic storm of March 1989, which was one of the largest geomagnetic disturbances of the twentieth century. Rapid geomagnetic field variation during this storm led to the induction of electric currents in the Earth's crust. These currents caused wide-spread blackouts across the Canadian Hydro-Quebec power grid, resulting in the loss of electric power to more than 6 million people (Allen, 1989; Czeck, 1992; Boteler, 1998; Kappenman, 1996, 2003; Thomson, 2010). If a similar storm-induced blackout had occurred in the Northeastern United States, the economic impact could have exceeded $10 billion (NRC, 2008; Baker et al., 2009; NRC report, 2009) not counting the negative impact on emergency services and the reduction in public safety associated with the loss of electric power in large cities.

GIC levels are primarily driven by impulsive geomagnetic disturbances created by the interaction between the Earth's magnetosphere and sharp velocity, density, and magnetic field enhancements in the solar wind. These disturbances result in ground-level time varying magnetic fields, which, when they reach high levels, produce GICs. On average, 200 days of strong to severe geomagnetic storms that could produce GICs on the surface of the Earth can be expected during a typical 11-year solar cycle (DoE-NERC, 2010). However, knowing exact levels of induced currents in power grid infrastructure during a geomagnetic event requires knowledge of deep earth conductivities and transmission line design parameters (NERC, 2012).

The USGS Geomagnetism Program, in collaboration with the USGS Crustal Geophysics Program, National Resources Canada, the NOAA Space Weather Prediction Center and NASA-Goddard GIC are building monitoring tools including a US-wide conductivity model , local magnetic field model and regional electric field estimates.

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