Geomagnetically induced currents during magnetic storms

The electric field which is induced by geomagnetic storms drives currents in technological systems, such as electric power transmission grids, oil and gas pipelines, telecommunication cables, and railway equipment. These geomagnetically induced currents (GIC) cause problems to the systems. In power grids, transformers may be saturated due to GIC resulting in harmful effects and possibly even to a collapse of the whole system, as occurred in Quebec in March 1989. Transformers may also suffer from permanent damage. In buried pipelines, GIC can enhance corrosion and interfere with corrosion control surveys. Telecommunication systems as well as railway equipment may also malfunction due to GIC. The electric and magnetic fields observed at the Earth's surface primarily depend on magnetospheric-ionospheric currents and secondarily on currents induced in the Earth. The physical background and modeling of GIC are discussed in this paper. Special attention is paid to basic principles necessarily understood to get an insight into GIC phenomena. Recent developments in the use of the Complex Image Method (CIM) permit fast and accurate computations of the electric field suitable for time-critical applications like GIC forecasting.