The Role of Global/Regional Earth Conductivity Models in Natural Geomagnetic Hazard Mitigation

Abstract

Geomagnetic disturbances cause perturbations in the Earth's magnetic field which, by the principle of electromagnetic induction, in turn cause electric currents to flow in the Earth. These geomagnetically induced currents (GICs) also enter man-made technological conductors that are grounded; notably, telegraph systems, submarine cables and pipelines, and, perhaps most significantly, electric power grids, where transformer groundings at power grid substations serve as entry points for GICs. The strength of the GICs that flow through a transformer depends on multiple factors, including the spatiotemporal signature of the geomagnetic disturbance, the geometry and specifications of the power grid, and the electrical conductivity structure of the Earth's subsurface. Strong GICs are hazardous to power grids and other infrastructure; for example, they can severely damage transformers and thereby cause extensive blackouts. Extreme space weather is therefore hazardous to man-made technologies. The phenomena of extreme geomagnetic disturbances, including storms and substorms, and their effects on human activity are commonly referred to as geomagnetic hazards. Here, we provide a review of relevant GIC studies from around the world and describe their common and unique features, while focusing especially on the effects that the Earth's electrical conductivity has on the GICs flowing in the electric power grids.

A Review of Geomagnetically Induced Current Effects on Electrical Power System: Principles and Theory

“…Based on the National Oceanic and Atmospheric Administration (NOAA) space weather scale, geomagnetic storms are classified into five levels. The space weather prediction centre (SWPC) forecasters predict levels of geomagnetics in a 3-day forecast based on discussion and analysis of CMEs [4,81,127,129]. In addition, machine learning techniques are another promising opportunity for predicting coronal mass ejections on the Sun and related GMDs [134].…”

“…There are different types of magnetometers, and variometers [152] are used in these sites, such as the search-coil magnetometer, an illustration of the search-coil design, flux-gate magnetometer, optically pumped magnetometer, nuclearprecision magnetometer, and hall-effect magnetometer. The recorded data from these sites are used to contribute to the magnetic field of the Earth globally and to determine ionospheric equivalent currents using the SECS method [4,153,154]. The magnetic field is measured from observatories in three dimensions, as illustrated in Fig.…”

“…Activities on the Sun, such as solar flares, coronal mass ejections (CMEs) and prominences, cause strong space weather and solar storms or geomagnetic disturbances (GMD) [1][2][3][4]. When these storms, or CMEs, strike the Earth, the magnetic field of the Earth, which provides natural protection against the fast-moving plasma, is compressed.…”

Induced telluric currents play a major role in the interpretation of geomagnetic variations

“…First of all, observations of the time derivative should be considered highly local, and any results derived from them should not be generalized to other locations without caution. It is well known that the electric field at the Earth's surface is highly local and 3-D conductivity structures strongly affect its variability (Kelbert, 2020). When comparing simultaneous measured time derivative values at different locations, it should be kept in mind that they do not necessarily provide a comparable measure of the dynamics of the driving ionospheric currents because they are affected by the internal anomalous fields.…”

Guest Editorial: Special Issue on “The 24th Electromagnetic Induction Workshop, Helsingør, Denmark”

“…The strength of the GICs that flow through a transformer depends on many factors, including the spatio-temporal signature of the geomagnetic storm, the geometry and specifications of the power grid, and the 3D distribution of electrical conductivity in the Earth's subsurface. Kelbert (2020) provides a comprehensive review of GIC studies from around the world, with a focus on the effects that the Earth's electrical conductivity, specially its 3D structures, has on the induced currents in the electric power grids.…”