Estimating ionospheric currents by inversion from ground-based geomagnetic data and calculating geoelectric fields for studies of geomagnetically induced currents

Villiers, J. S. de; Pirjola, Risto; Cilliers, Pierre J.

doi:10.1186/s40623-016-0530-1

Cited by 6 publications

(9 citation statements)

References 37 publications

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“…There are two equally valid formulations: The integral way is the calculation of the E field from the given current system and the surface impedance via the surface reflection coefficient R ( ν , ω ), without recourse to measured B fields beforehand. The E field Fourier integral [ De Villiers et al ., ] is

E_{y} ((),, x, ω) = i ω \frac{μ_{0} J ((), ω)}{2 π} true {true\int}_{0}^{\infty} ([], R ((),, ν, ω) - 1) ν^{prefix- 1} e^{prefix- ν h} normalcos ((), ν x) d ν .

For

R ((),, ν, ω) = \frac{i ω μ_{0} - ν Z ((), ω)}{i ω μ_{0} + ν Z ((), ω)}

, the field calculations give the same results in the integral method at the position ( x = 0 km) of the current system, as those computed from the direct method. The surface impedance Z ( ω ) is embedded in the reflection coefficient and computed from ground profiles.…”

Section: Methods and Proceduresmentioning

confidence: 99%

“…The integral way is the calculation of the E field from the given current system and the surface impedance via the surface reflection coefficient R(ν, ω), without recourse to measured B fields beforehand. The E field Fourier integral [De Villiers et al, 2016] is…”

Section: E Field Calculationmentioning

confidence: 99%

“…We build on the above theory with a new approach presented by De Villiers and Cilliers [2014] and De Villiers et al [2016]. They introduced geomagnetic inversion to obtain ionospheric current system parameters in the frequency ω and latitude x domain.…”

Section: Introductionmentioning

confidence: 99%

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Influences of various magnetospheric and ionospheric current systems on geomagnetically induced currents around the world

et al. 2017

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Ground‐based observations of geomagnetic field (B field) are usually a superposition of signatures from different source current systems in the magnetosphere and ionosphere. Fluctuating B fields generate geoelectric fields (E fields), which drive geomagnetically induced currents (GIC) in technological conducting media at the Earth's surface. We introduce a new Fourier integral B field model of east/west directed line current systems over a one‐dimensional multilayered Earth in plane geometry. Derived layered‐Earth profiles, given in the literature, are needed to calculate the surface impedance, and therefore reflection coefficient in the integral. The 2003 Halloween storm measurements were Fourier transformed for B field spectrum Levenberg‐Marquardt least squares inversion over latitude. The inversion modeled strengths of the equatorial electrojets, auroral electrojets, and ring currents were compared to the forward problem computed strength. It is found the optimized and direct results match each other closely and supplement previous established studies about these source currents. Using this model, a data set of current system magnitudes may be used to develop empirical models linking solar wind activity to magnetospheric current systems. In addition, the ground E fields are also calculated directly, which serves as a proxy for computing GIC in conductor‐based networks.

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E_{y} ((),, x, ω) = i ω \frac{μ_{0} J ((), ω)}{2 π} true {true\int}_{0}^{\infty} ([], R ((),, ν, ω) - 1) ν^{prefix- 1} e^{prefix- ν h} normalcos ((), ν x) d ν .

For

R ((),, ν, ω) = \frac{i ω μ_{0} - ν Z ((), ω)}{i ω μ_{0} + ν Z ((), ω)}

Section: Methods and Proceduresmentioning

confidence: 99%

Section: E Field Calculationmentioning

confidence: 99%

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Influences of various magnetospheric and ionospheric current systems on geomagnetically induced currents around the world

et al. 2017

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“…This comprehensive approach, however, makes a rather simplified assumption on the electrical conductivity structure of the Ethiopian lithosphere. A single 1D conductivity model is used for Ethiopia based on De Villiers et al (2016), which is, in turn, loosely adopted from the local profile at Addis Ababa out of the Alekseev et al (2015) compilation at depths above 100 km and a global profile Civet et al (2015) constrained by satellite data below 100 km. Notwithstanding the consideration that a 1D profile may not be an appropriate electrical conductivity model for all of Ethiopia, another concern might stem from the fact that the electrical resistivity of the upper crust (0.1-8 km depths) is set to 2e5 Ohm•m, a number substantially higher than is reasonable for the East African Rift.…”

Section: Chinamentioning

confidence: 99%

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

Kelbert

2019

Surv Geophys

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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.

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“…In each panel, the green stars identify the geographic location of the geomagnetic observatories used for this analysis. Despite previous investigations, in which sophisticated methods have been deployed to evaluate the geoelectric field (and hence GIC) over large regions (e.g., De Villiers J. S. et al, ; Püte et al, , and references therein), in the following we show maps evaluated through a simple spherical harmonics interpolation of E GIC as estimated by MA.I.GIC model from geomagnetic observations at each of the 74 ground stations. It is worth highlight that the blue region identified inside the Pacific (a and b) and Atlantic (c) Oceans, corresponding to low geoelectric field values, is an artifact generated by the absence of ground geomagnetic observatories used in this analysis.…”

Section: Magnetospheric and Ionospheric Contribution To Gicmentioning

confidence: 99%

Geoelectric Field Evaluation During the September 2017 Geomagnetic Storm: MA.I.GIC. Model

et al. 2019

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Estimating ionospheric currents by inversion from ground-based geomagnetic data and calculating geoelectric fields for studies of geomagnetically induced currents

Cited by 6 publications

References 37 publications

Influences of various magnetospheric and ionospheric current systems on geomagnetically induced currents around the world

Influences of various magnetospheric and ionospheric current systems on geomagnetically induced currents around the world

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

Geoelectric Field Evaluation During the September 2017 Geomagnetic Storm: MA.I.GIC. Model

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