Rapid prediction of electric fields associated with geomagnetically induced currents in the presence of three‐dimensional ground structure: Projection of remote magnetic observatory data through magnetotelluric impedance tensors

Abstract

Ground level electric fields arising from geomagnetic disturbances (GMDs) are used by the electric power industry to calculate geomagnetically induced currents (GICs) in the power grid. Current industry practice is limited to electric fields associated with 1‐D ground electrical conductivity structure, yet at any given depth in the crust and mantle lateral (3‐D) variations in conductivity can span at least 3 orders of magnitude, resulting in large deviations in electric fields relative to 1‐D models. Solving Maxwell's equations for electric fields associated with GMDs above a 3‐D Earth is computationally burdensome and currently impractical for industrial applications. A computationally light algorithm is proposed as an alternative. Real‐time data from magnetic observatories are projected through multivariate transfer functions to locations of previously occupied magnetotelluric (MT) stations. MT time series and impedance tensors, such as those publically available from the NSF EarthScope Program, are used to scale the projected magnetic observatory data into local electric field predictions that can then be interpolated onto points along power grid transmission lines to actively improve resilience through GIC modeling. Preliminary electric field predictions are tested against previously recorded time series, idealized transfer function cases, and existing industry methods to assess the validity of the algorithm for potential adoption by the power industry. Some limitations such as long‐period diurnal drift are addressed, and solutions are suggested to further improve the method before direct comparisons with actual GIC measurements are made.

Telluric Field Variations as Drivers of Variations in Cathodic Protection Potential on a Natural Gas Pipeline in New Zealand

“…In recent years the risk posed to electrical power networks by space weather has been extensively studied in many parts of the world (e.g., Beggan et al, ; Blake et al, ; Bonner & Schultz, ; Divett et al, ; Gaunt & Coetzee, ; Ingham et al, ; Liu et al, ; Marshall et al, ; Torta et al, , , ; Trivedi et al, ). As recently reiterated by Boteler and Pirjola (), such risk arises from geomagnetically induced currents (GICs) driven by the electromotive force induced in long transmission lines.…”

Modeling Geoelectric Fields in Ireland and the UK for Space Weather Applications

“…The modeling of geoelectric fields, as a result of Earth's response to magnetic field variations, was performed in several studies assuming a homogeneous or a 1-D Earth for simplification. However, the complexity of the subsurface geology has motivated recent works to consider a more realistic 3-D Earth when estimating the geoelectric fields (Bonner & Schultz, 2017;Ivannikova et al, 2018;Kelbert et al, 2017;Weigel, 2017), which provides more accurate results when modeling the GICs (Torta et al, 2017).…”

Modeling Geomagnetically Induced Currents in Australian Power Networks Using Different Conductivity Models

“…When the impedance tensors for sites 79 and 80 are converted to apparent resistivity and plotted in log‐log scale (Figures a and b, respectively), it clearly shows that the measured apparent resistivity curve for site 79 is shifted by a constant reference to the modeled 3DM apparent resistivity. This is a typical static shift distortion effect in the amplitude of the measured impedance tensor for site 79, manifesting itself in the apparent resistivity, which can vary from site to site due to near surface resistivity inhomogeneities (Bonner & Schultz, ). This mismatch in amplitude is primarily contributed to static shift distortion in the measured impedance tensor.…”