Geoelectric hazard assessment: the differences of geoelectric responses during magnetic storms within common physiographic zones

Cuttler, Stephen W.; Love, Jeffrey J.; Swidinsky, Andrei

doi:10.1186/s40623-018-0807-7

Cited by 10 publications

(10 citation statements)

References 29 publications

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“…Those developed for North America (Blum et al, ; Fernberg, ; Ferguson & Odwar, ) have been used to estimate benchmarks for NERC and in numerous related studies (e.g., Marti et al, ; Nikitina et al, ; Ngwira et al, ; Pulkkinen et al, ; Trichtchenko et al, ; Wei et al, ); indeed, 1‐D models are sometimes treated as first‐order representations of the Earth (e.g., Boteler, ; Butala et al, ; Gannon et al, ; Marti et al, ). Despite this, several studies have shown that the use of some 1‐D models (e.g., Fernberg, ) can give estimated geoelectric amplitudes that are erroneous by more than an order of magnitude (in some cases, the error exceeds 2 orders of magnitude; e.g., Bedrosian & Love, ; Cuttler et al, ; Love, Rigler, et al, ; Lucas et al, ). Furthermore, the magnetotelluric community routinely uses measured impedance tensors, such as those summarized in Figure , to construct regional models of subsurface electrical conductivity structure that are far from 1‐D, including for the Pacific Northwest (e.g., Bedrosian & Feucht, ; Meqbel et al, ; Patro & Egbert, ).…”

Section: Magnetotelluric Impedance Tensorsmentioning

confidence: 99%

Geoelectric Hazard Maps for the Pacific Northwest

et al. 2018

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Maps of extreme value, horizontal component geoelectric field amplitude are constructed for the Pacific Northwest United States (and parts of neighboring Canada). Multidecade long geoelectric field time series are calculated by convolving Earth surface impedance tensors from 71 discrete magnetotelluric survey sites across the region with historical 1-min (2-min Nyquist) geomagnetic variation time series obtained from two nearby observatories. After fitting statistical models to 1-min geoelectric amplitudes realized during magnetic storms, extrapolations are made to estimate threshold amplitudes that are only exceeded, on average, once per century. One hundred-year geoelectric exceedance amplitudes range from 0.06 V/km at a survey site in western Washington State to 9.47 V/km at a site in southeast British Columbia; 100-year geoelectric exceedance amplitudes equal 7.10 V/km at a site north of Seattle and 2.28 V/km at a site north of Portland. Systematic and random errors are estimated to be less than 20%, much less than site-to-site differences in geoelectric amplitude that arise from site-to-site differences in surface impedance. Maps of 100-year exceedance amplitudes are compared with the peak geoelectric amplitudes realized during the March 1989 magnetic superstorm; it is noted that some storms of relatively modest intensity can generate localized geoelectric fields of relatively high amplitude. The geography of geoelectric hazard across the Pacific Northwest is closely related to known geologic and tectonic structures.

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Section: Magnetotelluric Impedance Tensorsmentioning

confidence: 99%

Geoelectric Hazard Maps for the Pacific Northwest

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“…The 1‐D conductivity models of Fernberg () and the USArray 3‐D impedance tensors available from the Incorporated Research Institutions for Seismology (IRIS) Searchable Product Depository (http://ds.iris.edu/spud/emtf) provide impedance information for large regions across the contiguous United States. Several recent studies have utilized both the 1‐D and 3‐D impedance tensors in the calculation of the surface electric field for purposes of space weather threat assessment (Bedrosian & Love, ; Bonner & Schultz, ; Butala et al, ; Cuttler et al, ; Gannon et al, ; Love et al, , , ; Lucas et al, ; Weigel, ).…”

Section: Introductionmentioning

confidence: 99%

The Impact of Magnetic Field Temporal Sampling on Modeled Surface Electric Fields

et al. 2018

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Descriptions of the surface magnetic-to-electric field relationship, using magnetotelluric impedance tensors, have seen refinement in recent years. Correspondingly, models of geomagnetically induced currents flowing in power line conductors using input from more fundamental observables (e.g., the surface magnetic field or solar wind drivers) have become more sophisticated. Magnetometer data used for purposes of surface electric field modeling typically have cadences between 1 s and 1 min. Using 1-D and 3-D magnetotelluric impedance tensors, we quantify the effect of magnetometer cadence on modeled peak surface electric fields during the 22 geomagnetic storms. It is shown that 1-min magnetometer data sampling leads to median biases in the peak electric field of 10-20% magnitude attenuation and 2-17 ∘ in direction (depending on the storm) across the United States using the Fernberg 1-D conductivity models and 11-26% (0.9-8 ∘ ) using the 3-D impedance tensors derived from the USArray magnetotelluric survey. The largest 10% of attenuations almost entirely occur near low-resistivity subsurface structures in the western and eastern United States, reaching a 50% median attenuation during the 17 March 2015 event. It is concluded that cadence, local geology, and the spectral content of the geomagnetic field all play a significant role in the bias.Under the standard magnetotelluric assumptions (neglect of displacement and polarization currents, free-space permeability, and quasi-uniformity of the source field; Chave & Weidelt, 2012, and

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“…From this study, we learn that E3 EMP geoelectric fields, generated by a nuclear explosion in the near-Earth space environment above our heads, can be strongly affected by the geography of the Earth's surface impedance, a tensor that is a function of threedimensional geological structures beneath our feet. This qualitative point might have been anticipated from previous analyses in which synthetic magnetic signals [e.g., Bedrosian and Love, 2015;McKay and Whaler , 2006] and measured magnetic-storm variation [e.g., Cuttler et al, 2018;Kelbert et al, 2017;Lucas et al, 2018] are convolved with long-period (< 10 −1 Hz; > 10 s) magnetotelluric impedance tensors. Local surface impedance can have a significant effect on the amplitude, polarization, and variational phase of local induced geoelectric fields.…”

Section: Conclusion and Discussionmentioning

confidence: 72%