Estimating the electric field response to the Halloween 2003 and September 2017 magnetic storms across Scotland using observed geomagnetic fields, magnetotelluric impedances and perturbation tensors
Estimating the electric field response to the Halloween 2003 and September 2017 magnetic storms across Scotland using observed geomagnetic fields, magnetotelluric impedances and perturbation tensors
Geomagnetic storms generate heightened magnetovariational activity, which induces electric fields that drive hazardous currents known as geomagnetically induced currents (GICs) through man-made technological conductors including power transmission lines, railway networks and gas pipelines. We multiply magnetotelluric (MT) impedances from 23 sites in Scotland and northern England with measured geomagnetic field spectra from the Halloween 2003 and September 2017 storms to estimate maximum peak-to-peak, electric field magnitudes and directions for these storms, which we present as hazard maps. By sampling these electric fields in the direction of the longest (>50 km), high-voltage (275 and 400 kV) Scottish power transmission lines and integrating along their lengths, we estimate their associated transmission-line voltages. Lateral electrical conductivity variations in the Earth generate horizontal magnetic field gradients. We investigate the effect of these gradients on electric field estimates obtained using remote magnetic fields by applying a correction to the impedance tensor derived from the magnetic perturbation tensor between the local MT site and the remote magnetic field site. For the September 2017 storm, we also compare our estimated electric fields with a unique dataset comprising measured storm-time electric fields from 7 MT sites. We find that peak-to-peak, electric field magnitudes may have reached 13 V/km during the Halloween storm in some areas of the Scottish Highlands, with line-averaged electric fields >5 V/km sustained along a number of long-distance, high-voltage power transmission lines; line-averaged electric fields for the September 2017 storm are 1 V/km or less. Our surface electric fields show significant site-to-site variability that arises due to Earth’s internal 3D electrical conductivity structure, as characterised by the MT impedance tensors.
Eelectric fields, Geomagnetically induced currents, Hazard maps, Magnetic storms, Magnetotellurics
Simpson, Fiona
98408e5e-6c71-42b7-9425-fa31d094b277
Bahr, Karsten
bff64fd0-24a1-4706-8344-c1b17a55c9bc
7 October 2020
Simpson, Fiona
98408e5e-6c71-42b7-9425-fa31d094b277
Bahr, Karsten
bff64fd0-24a1-4706-8344-c1b17a55c9bc
Simpson, Fiona and Bahr, Karsten
(2020)
Estimating the electric field response to the Halloween 2003 and September 2017 magnetic storms across Scotland using observed geomagnetic fields, magnetotelluric impedances and perturbation tensors.
Journal of Space Weather and Space Climate, 10, [2020049].
(doi:10.1051/swsc/2020049).
Abstract
Geomagnetic storms generate heightened magnetovariational activity, which induces electric fields that drive hazardous currents known as geomagnetically induced currents (GICs) through man-made technological conductors including power transmission lines, railway networks and gas pipelines. We multiply magnetotelluric (MT) impedances from 23 sites in Scotland and northern England with measured geomagnetic field spectra from the Halloween 2003 and September 2017 storms to estimate maximum peak-to-peak, electric field magnitudes and directions for these storms, which we present as hazard maps. By sampling these electric fields in the direction of the longest (>50 km), high-voltage (275 and 400 kV) Scottish power transmission lines and integrating along their lengths, we estimate their associated transmission-line voltages. Lateral electrical conductivity variations in the Earth generate horizontal magnetic field gradients. We investigate the effect of these gradients on electric field estimates obtained using remote magnetic fields by applying a correction to the impedance tensor derived from the magnetic perturbation tensor between the local MT site and the remote magnetic field site. For the September 2017 storm, we also compare our estimated electric fields with a unique dataset comprising measured storm-time electric fields from 7 MT sites. We find that peak-to-peak, electric field magnitudes may have reached 13 V/km during the Halloween storm in some areas of the Scottish Highlands, with line-averaged electric fields >5 V/km sustained along a number of long-distance, high-voltage power transmission lines; line-averaged electric fields for the September 2017 storm are 1 V/km or less. Our surface electric fields show significant site-to-site variability that arises due to Earth’s internal 3D electrical conductivity structure, as characterised by the MT impedance tensors.
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Accepted/In Press date: 31 August 2020
e-pub ahead of print date: 7 October 2020
Published date: 7 October 2020
Additional Information:
Funding Information:
Acknowledgements. This work was supported by the Natural Environment Research Council (NERC Grant NE/ P016782/1). We thank Forestry Commission Scotland, National Trust for Scotland and Glen Tanar Estate for allowing us to install MT instrumentation on their land. MT data collected by the authors will be made available through the National Geoscience Data Centre (NGDC), UK by the end of the project (December 2021). The results presented in this paper also rely on geomagnetic data collected at ESK geomagnetic observatory at the end of October 2003. We thank the British Geological Survey (BGS) for supporting its operation and INTERMAGNET for promoting high standards of magnetic observatory practice. Maps were generated using the Generic Mapping Tool, GMT (Wessel et al., 2013). We also thank Benjamin Murphy and an anonymous reviewer for thoughtful reviews that helped us to improve an earlier version of our manuscript. The editor thanks Ari Viljanen and Benjamin Murphy for their assistance in evaluating this paper.
Publisher Copyright:
© F. Simpson & K. Bahr, Published by EDP Sciences 2020.
Keywords:
Eelectric fields, Geomagnetically induced currents, Hazard maps, Magnetic storms, Magnetotellurics
Identifiers
Local EPrints ID: 444550
URI: http://eprints.soton.ac.uk/id/eprint/444550
PURE UUID: b707ca7a-32da-47c6-a8e0-ff8cf6902ded
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Date deposited: 23 Oct 2020 16:33
Last modified: 16 Mar 2024 09:32
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Author:
Karsten Bahr
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