Technical Article

Nowcasting geoelectric fields in Ireland using magnetotelluric transfer functions

¹ Astronomy & Astrophysics Section, DIAS Dunsink Observatory, Dublin Institute for Advanced Studies, Dublin D15 XR2R, Ireland
² School of Physics, Trinity College Dublin, Dublin D02 PN40, Ireland
³ South East Technological University, Carlow R93 V960, Ireland
⁴ Geological Survey Ireland, Dublin A94 N2R6, Ireland
⁵ Department of Geophysics, University of Oslo, Oslo 0316, Norway
⁶ Geophysics Section, Dublin Institute for Advanced Studies, Dublin D02 Y006, Ireland

^* Corresponding author: jmalone@cp.dias.ie

Received: 2 August 2022
Accepted: 7 February 2023

Abstract

Geomagnetically induced currents (GIC) driven by geoelectric fields pose a hazard to ground-based infrastructure, such as power grids and pipelines. Here, a new method is presented for modelling geoelectric fields in near real time, to provide valuable information to help mitigate the impact of GIC. The method uses magnetic field measurements from the Magnetometer Network of Ireland (MagIE; https://www.magie.ie), interpolates the geomagnetic field variations between magnetometers using spherical elementary current systems (SECS), and estimates the local electric field using a high-density (< 40 km) network of magnetotelluric transfer functions (MT-TF) encompassing the island. The model was optimised to work in near real time, with a correction curve applied to the geoelectric field time series. This approach was successfully validated with measured electric fields at four sites for a number of geomagnetic storms, providing accurate electric fields up to a 1-minute delay from real time, with high coherence (0.70 – 0.85) and signal-to-noise ratio (SNR; 3.2 – 6.5) relative to measured electric field validation time series. This was comparable to a standard non-real-time geoelectric field model (coherence = 0.80 − 0.89 and SNR = 4.0 − 7.0). The impact of galvanic distortion on the model was also briefly evaluated, with a galvanic distortion correction leading to a more homogeneous representation of the direction of the electric field, at a regional scale.