
The geoelectric field is a measure of the induction hazard to man-made conductors, such as electrical power lines, that results from geomagnetic activity, and can be used to estimate the amount of current induced by integrating along the conducting pathway. The US-Canada-1D geoelectric field model uses 1D conductivity models over the lower 48 United States and over Canada up to 60 degrees latitude, with output spatial resolution of 1/2 degree in latitude and longitude. The official NWS product notification is available here and contains information on how to provide feedback during the 30 day comment period from April 4 - May 4.
The near real-time US-Canada-1D E-field mapping project is a joint effort between NOAA/SWPC and NRCan/CHIS Space Weather, in collaboration with the USGS geomagnetism group and the NASA/CCMC.
Background
Potentially hazardous geoelectric fields can be induced during geomagnetic storms. These geomagnetic storms are a form of space weather driven by enhanced currents in Earth's magnetosphere and ionosphere and are observed at ground level as a time-varying magnetic field. As is well known from Faraday's law, a time-varying magnetic field induces currents along natural and artificial conducting pathways. This geoelectric field product combines information about the time-varying magnetic field together with Earth-conductivity information to estimate regional geoelectric fields. The amount of current induced in an artificial conductor may be calculated by integrating the geoelectric field along the conducting pathway. When currents are induced in artificial conductors, unexpected and sometimes problematic effects can occur in the operation of the affected equipment. Please see the article about the effect this has on electrical power systems at https://www.swpc.noaa.gov/impacts/electric-power-transmission. Please see also the article Modeling geomagnetically induced currents, by Boteler and Pirjola in Space Weather (31 January 2017), for an up-to-date description of this phenomena.
Versions and Caveats:
This version of the US-Canada electric field maps uses 1D physiographic conductivity models with the U.S. portion developed by the Electric Power Research Institute (EPRI – 2020) and the Canadian portion described by Trichtchenko et al. (2019). Users please note that there is also a 3D empirical version of the Geoelectric Field Maps (for the continental US only) running at SWPC (deployed to operations in FY2020); The 3D empirical model uses Magnetotelluric Transfer Functions (EMTF's) (see Kelbert et al., 2011 for details), which provide an Earth Conductivity description that incorporates the full 3D effects of Earth conductivity structures. The coverage area of the 3D empirical model is limited to locations where MT surveys have been published. In general we recommend that users located in the 3D empirical model coverage area use that model instead of the 1D model. The US-Canada-1D map, however, covers a larger area, using available information, and is being released experimentally to facilitate scientific research, validation, and familiarization for the operators.
Acknowledgements:
Key data provider agencies are gratefully acknowledged for their contributions:
- The U.S. magnetic observatories are operated and maintained by the U.S. Geological Survey
- The Canadian magnetic observatories are operated and maintained by Natural Resources Canada
- Updated 1D models for the U.S. were provided courtesy of the Electric Power Research Institute (EPRI Product ID 3002019425, June 08, 2020, Use of Magnetotelluric Measurement Data to Validate/Improve Existing Earth Conductivity Models)
The maps use a geomagnetic-field time series interpolation algorithm (Spherical Elementary Current Systems) developed and made available courtesy of the Finnish Meteorological Institute (Amm & Viljanen, 1999; Pulkkinen et al., 2003)
References:
Amm, O. & A. Viljanen (1999). Ionospheric disturbance magnetic field continuation from the ground to the ionosphere using spherical elementary current systems, Earth Planets Space, 51, 431-440.
Bedrosian, P.A., A Kelbert, B.L. Burton, J.R. Morris, and C. Blum (2015). Long Period Magnetotelluric Transfer Functions from the Florida Peninsula. doi:10.17611/DP/EMTF/USGS/GEOMAG/FL15
Bedrosian, P. A., & Love, J. J. (2015). Mapping geoelectric fields during magnetic storms: Synthetic analysis of empirical United States impedances. Geophysical Research Letters, 42(23).
Bonner, L. R., & Schultz, A. (2017). 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. Space Weather, 15(1), 204-227.
Boteler, D. & R. Pirjola (2017), Modeling geomagnetically induced currents, Space Weather, DOI10.1002/2016SW001499 (31 January 2017).
Boteler, D.H. and Pirjola, R.J. (2022), Electric Field Calculations for Real-Time Space Weather Alerting Systems, Geophys. J. Int., https://doi.org/10.1093/gji/ggac104
Kelbert, A., G.D. Egbert and A. Schultz (2011), IRIS DMC Data Services Products: EMTF, The Magnetotelluric Transfer Functions, https://doi.org/10.17611/DP/EMTF.1
Kelbert, A., Balch, C. C., Pulkkinen, A., Egbert, G. D., Love, J. J., Rigler, E. J., & Fujii, I. (2017). Methodology for time‐domain estimation of storm‐time geoelectric fields using the 3D magnetotelluric response tensors. Space Weather.
Meqbel, N. M., Egbert, G. D., Wannamaker, P. E., Kelbert, A., & Schultz, A. (2014). Deep electrical resistivity structure of the northwestern US derived from 3-D inversion of USArray magnetotelluric data. Earth and Planetary Science Letters, 402, 290-304.
Murphy, B. S., & Egbert, G. D. (2017). Electrical conductivity structure of southeastern North America: Implications for lithospheric architecture and Appalachian topographic rejuvenation. Earth and Planetary Science Letters, 462, 66-75.
Pulkkinen, A., O. Amm, A. Viljanen, et al. (2003). Separation of the geomagnetic variation field on the ground into external and internal parts using the spherical elementary current system method, Earth Planets Space, 55, 117-129.
Sun, J., Kelbert, A., & Egbert, G. D. (2015). Ionospheric current source modeling and global geomagnetic induction using ground geomagnetic observatory data. Journal of Geophysical Research: Solid Earth, 120(10), 6771-6796.
Trichtchenko, L., Fernberg, P.A., Boteler, D. (2019). One-dimensional Layered Earth Models of Canada for GIC Applications, Geological Survey of Canada Open Files 8594 & 8595.
Weigel, R. S. (2017). A comparison of methods for estimating the geoelectric field. Space Weather, 15(2), 430-440.
Yang, B., Egbert, G. D., Kelbert, A., & Meqbel, N. M. (2015). Three-dimensional electrical resistivity of the north-central USA from EarthScope long period magnetotelluric data. Earth and Planetary Science Letters, 422, 87-93.
The US-Canada Geoelectric Field Maps using 1D models is planned to replace the original US-only1D model sometime in 2022 or 2023.
Recent quantitative results for the US-Canada-1D model can be found in geojson format here:
https://services.swpc.noaa.gov/experimental/json/lists/rgeojson/US-Canada-1D/
Recent quantitative results for the empirical EMTF model in geojson format can be found here:
https://services.swpc.noaa.gov/json/lists/rgeojson/InterMagEarthScope/
Archive maps and data for the Geoelectric Field Maps are available by request.