Developing a new ground electric field model for the UK based on long-period magnetotelluric data for the SWIMMR N4 (SAGE) framework

Huebert, J.; Eaton, E.; Beggan, C.D.. 2024 Developing a new ground electric field model for the UK based on long-period magnetotelluric data for the SWIMMR N4 (SAGE) framework. Edinburgh, UK, British Geological Survey, 42pp. (OR/24/022) (Unpublished)

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Abstract/Summary

The large variations in ground electric field across the country during a geomagnetic storm drive so-called geomagnetically induced current (GICs), a major geohazard to ground-based technological infrastructure such as electrical transformers at high voltage substations, gas pipelines and railway signalling. This report describes the collection of data and modelling work required to create a new ground electric field model for the UK developed by the SWIMMR N4 (SAGE) project. The model is based on new long-period magnetotelluric (MT) data collected across Britain during the SAGE project along with legacy MT data from previous surveys. MT data sense the electrical conductivity of the rocks in the subsurface down to large depths and allow images of the subsurface structure to be inverted for using sophisticated computational methods. In this report, we describe the methodology, the fieldwork campaign to collect the MT data at 44 sites in Britain during a two-year field campaign from April 2021 to August 2023 and initial results of geoelectric field modelling. At each site, timeseries of electric and magnetic field variations were recorded continuously and simultaneously for several weeks. The raw data were then processed into MT impedance tensors at each site. The MT impedance data are then used to model geoelectric fields during geomagnetic storm times, showing large variations across the country due to the varying geology. A brief overview of the legacy MT data available from previous space weather-related projects and two historic MT campaigns are described. We examine the modelled geoelectric field during the September 2017 and March 1989 geomagnetic storms using magnetic field measurements and the MT impedance tensor estimates. For example, in central Yorkshire the electric field estimates are about one-tenth of the magnitude observed in Lincolnshire around 100 km distant to the south, illustrating the spatial variability of the geoelectric field due to the underlying geology. An outline for the implementation of ground electric field modelling for the now- and forecast framework in the SWIMMR N4 (SAGE) cloud-based modelling service is then presented. Our approach uses the MT impedances and magnetic field data measured at geomagnetic observatories across the UK. Some measures to account for the limitations of frequency-domain modelling are applied. In the future, the geoelectric field modelling can be based on a full 3D inversion model of UK subsurface electrical conductivity using the MT data collected. We also briefly outline how the new model in combination with the decades-long magnetic field observations in the UK will be used to assess space weather hazards in the context of extreme value analysis and hazard maps.

Item Type:	Publication - Report
Funders/Sponsors:	British Geological Survey, NERC, STFC
Additional Information. Not used in RCUK Gateway to Research.:	This item has been internally reviewed, but not externally peer-reviewed.
Date made live:	04 Sep 2024 11:10 +0 (UTC)
URI:	https://nora.nerc.ac.uk/id/eprint/537960

Item Type:

Publication - Report

Funders/Sponsors:

British Geological Survey, NERC, STFC

Additional Information. Not used in RCUK Gateway to Research.:

This item has been internally reviewed, but not externally peer-reviewed.

Date made live:

04 Sep 2024 11:10 +0 (UTC)

URI:

https://nora.nerc.ac.uk/id/eprint/537960