page_title: Geomagnetically induced current
section_title: Risk to infrastructure
hierarchical_section_title: Geomagnetically induced current / Risk to infrastructure
caption_attribution_description: English: The basic principle for the generation of GIC: variations of the ionospheric currents (I(t)) generate an electric field (E(t)) driving GIC. Shown are also real GIC recordings from the Finnish natural gas pipeline. Svenska: Inducerade strömmar, med data från en gasledning i Finland. Illustration av hur elektriska strömmar i jonosfären orsakar strömmar i elnätet och i pipelines genom elektromagnetisk induktion. Infällt visas också verkligen uppmätt ström i en finsk gaspipeline. English: Schematic illustration of generation of GIC.
context_page_description: Geomagnetically induced currents, affecting the normal operation of long electrical conductor systems, are a manifestation at ground level of space weather. During space weather events, electric currents in the magnetosphere and ionosphere experience large variations, which manifest also in the Earth's magnetic field. These variations induce currents in conductors operated on the surface of Earth. Electric transmission grids and buried pipelines are common examples of such conductor systems. GIC can cause problems, such as increased corrosion of pipeline steel and damaged high-voltage power transformers. GIC are one possible consequence of geomagnetic storms, which may also affect geophysical exploration surveys and oil and gas drilling operations.
context_section_description: A time-varying magnetic field external to the Earth induces telluric currents—electric currents in the conducting ground. These currents create a secondary (internal) magnetic field. As a consequence of Faraday's law of induction, an electric field at the surface of the Earth is induced associated with time variations of the magnetic field. The surface electric field causes electrical currents, known as geomagnetically induced currents (GIC), to flow in any conducting structure, for example, a power or pipeline grid grounded in the Earth. This electric field, measured in V/km, acts as a voltage source across networks.
  Examples of conducting networks are electrical power transmission grids, oil and gas pipelines, non-fiber optic undersea communication cables, non-fiber optic telephone and telegraph networks and railways. GIC are often described as being quasi direct current (DC), although the variation frequency of GIC is governed by the time variation of the electric field. For GIC to be a hazard to technology, the current has to be of a magnitude and occurrence frequency that makes the equipment susceptible to either immediate or cumulative damage. The size of the GIC in any network is governed by the electrical properties and the topology of the network. The largest magnetospheric-ionospheric current variations, resulting in the largest external magnetic field variations, occur during geomagnetic storms and it is then that the largest GIC occur. Significant variation periods are typically from seconds to about an hour, so the induction process involves the upper mantle and lithosphere. Since the largest magnetic field variations are observed at higher magnetic latitudes, GIC have been regularly measured in Canadian, Finnish and Scandinavian power grids and pipelines since the 1970s. GIC of tens to hundreds of amperes have been recorded. GIC have also been recorded  at mid-latitudes during major storms. There may even be a risk to low latitude areas, especially during a storm commencing suddenly because of the high, short-period rate of change of the field that occurs on the day side of the Earth.
  GIC were first observed on the emerging electric telegraph network in 1847–8 during Solar cycle 9. Technological change and the growth of conducting networks have made the significance of GIC greater in modern society. The technical considerations for undersea cables, telephone and telegraph networks and railways are similar. Fewer problems have been reported in the open literature, about these systems. This suggests that the hazard is less today, or that there are reliable methods of equipment protection.
caption: The basic principle for the generation of GIC: variations of the ionospheric currents (I(t)) generate an electric field (E(t)) driving GIC. Shown are also real GIC recordings from the Finnish natural gas pipeline.
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