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

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.