geomagnetically induced currents (GIC)


When the sun erupts with what's called a coronal mass ejection or CME, a cloud of solar material achieves escape velocity and hurtles toward Earth.  Once it makes contact with the magnetic envelope that surrounds our planet, it can cause Earth's magnetic environment to continually change in shape and strength over the course of a day or two, a situation known as a geomagnetic storm.

Changing magnetic fields cause electricity to flow and vice versa, so these quick changes of the magnetic fields inherently create electrical currents down on the ground.  These currents, known as geomagnetically induced currents (GICs) flow underground as much as 60 miles in anything that can conduct electricity, such as power grids, oil pipes, telephone lines, or railway tracks.

In power grids, these currents can damage transformers and cause blackouts.  In oil pipelines and railway tracks, GICs can increase corrosion of the steel or cause erroneous signal changes, respectively. In communication lines, the GICs will disrupt the information traveling through the wires.

To give operators of power systems advance warning, Solar Shield has developed a two-level forecasting system. 

Level 1 GIC forecasts: The first level of forecasting offers a one- to two-day lead time based on observations of events on the sun and computer models of the magnetic system between the sun and Earth.  These forecasts are partly probabilistic. 

Level 2 GIC forecasts: The second level of forecasting is fully deterministic.  These forecasts use in situ measurements of the speed and direction of solar material as it moves toward Earth to drive computer models.  This second level of forecasting can offer 15- to 60-minutes of lead time.

Caption: A schematic illustration of how geomagnetically induced currents  or GICs are generated. Variations in the magnetic fields and electric currents near Earth (illustrated as a loop at the top of the figure) induce an electric field at the surface of Earth. This electric field can drive GICs in power grids and oil pipelines. 

Caption: The process used to generate Level 1 GIC forecasts. Observations of solar coronal mass ejections (CMEs) are used to drive a computer model of the magnetic system between the sun and Earth. The model forecasts the interplanetary conditions at Earth’s orbit as a result of the CME. An algorithm is then applied to the forecasted interplanetary conditions in order to forecast GICs at individual nodes of the power grid. The final output of the system is a text file of GIC forecasts, which is uploaded to the Electric Power Research Institute for their GIC display tool used by the power transmission industry.

Caption: The process used to generate Level 2 GIC forecasts. NASA's Advanced Composition Explorer (ACE) spacecraft observes the movement of solar material as it nears Earth.  These observations are used to drive computer models of the near-Earth magnetic system, which in turn can help compute GIC activity at individual points along the power transmission system. The final output of the system is again a text file of GIC forecasts, which is uploaded to the Electric Power Research Institute. 

For more details on the experimental forecasting system and the techniques used in Solar Shield, see the PUBLICATIONS/REPORTS section or contact the project point of contact.

GICs have been known to cause numerous problems in high-voltage transmission grids, and a recent report by the US National Research Council found that the threat posed by a GIC could potentially be catastrophic.  The best-known examples of problems are the blackout of the Quebec province in Canada in March 1989 and the city of Malmö in Sweden in October 2003.  There was also substantial damage experienced by number of South-African power transformers in October and November 2003.