ated with power transmission can flow on the grid. These geomagnetically induced currents (GICs) have the potential to overload transformers, causing, at a minimum, reductions in efficiency. Large-amplitude GICs can age, or even destroy, a transformer.

Owing to the critical place electric power has in the maintenance of society, a number of recent studies4,5,6 have emphasized the need for further research with the objective to understand, and then prevent and mitigate, deleterious GIC-based hazards. Ground-based assets such as long-distance pipelines are also susceptible, responding to the strong currents induced by geomagnetic storms. Some of the many manifestations of disturbances from the Sun that now have the potential to disrupt society are illustrated in Figure 3.4.

Severe Solar Storms

Powerful solar flares (e.g., see Figure 3.5) and their accompanying ejections of mass and energetic particles occur episodically. In an extreme event in 1859, a large solar eruption triggered a geomagnetic storm that sparked fires in telegraph offices across the United States and triggered aurorae as far south as Central America. Such a powerful event directly striking Earth today could severely affect the power grid, destroying transformers and causing widespread outages.

Although during the space age a direct hit of this magnitude has not yet occurred, severe solar storms have nevertheless damaged spacecraft and power grids, producing, for example, widespread power outages in Quebec in 1989 and in South Africa in 2003. Very energetic solar particles (SEPs) that are accelerated in solar flares and Earth-ward-propagating interplanetary shocks penetrate along open magnetic field lines into Earth’s polar ionosphere, where they degrade high-frequency communications over the poles. This interference forces the airline industry to reroute transpolar flights, at a significant cost in time and fuel. European flight crews on shorter high-latitude routes are categorized as “radiation workers” and are monitored by film badges because of their increased exposure to SEPs. Lacking the knowledge for predictive mitigation of severe solar storm impacts, operators currently simply assume (and hope) that the rarity of extreme events and the vastness of space will protect against the most deleterious consequences.

Although particularly intense events occur about once per solar cycle and strong to extreme particle storms can occur about 15 times per cycle, somewhat less intense geomagnetic storms occur even more often. Even during these weaker geomagnetic storms, large changes in ionospheric currents threaten transformers in long-distance east-west power lines in North America and northern Europe.

THE CHALLENGE OF PREDICTING SPACE WEATHER EVENTS

Science cannot now reliably predict, with sufficient warning, the disturbances from space that might threaten society at any particular time. The physical processes that control space weather differ in complex ways from those that control the weather of the neutral atmosphere of Earth. Within the entire system numerous phenomena have to be addressed on a wide range of physical scales—for example, the gas density can vary from 1019 in Earth’s atmosphere to just a few particles per cubic centimeter in the solar wind, and the relevant scale lengths can vary from centimeters to astronomical units (AUs). The many different and complex interactions include electromagnetic forces that accelerate and control the flow of

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4 J. Kappenmann, Metatech Corporation, Low-Frequency Protection Concepts for the Electric Power Grid: Geomagnetically Induced Current (GIC) and E3 HEMP Mitigation, prepared for Oak Ridge National Laboratory, Oak Ridge, Tenn., January 2010.

5 MITRE Corporation, Impacts of Severe Space Weather on the Electric Grid, JASON report, McLean, Va., November 2011.

6 North American Electric Reliability Corporation, 2012 Special Reliability Assessment Interim Report: Effects of Geomagnetic Disturbances on the Bulk Power System, February 2012, available at http://www.nerc.com/files/2012GMD.pdf.



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