Geoelectric field modelling for canadian space weather services

Trichtchenko, Larisa; Fernberg, P.; Danskin, D. W.

doi:10.4095/299116

Cited by 3 publications

(3 citation statements)

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“…We have previously used similar empirically based methods in analyzing geoelectric hazards for other parts of the continental United States (e.g., Love et al, , ; Lucas et al, ). Our methods stand in distinct contrast to analyses of geoelectric hazards (e.g., Gannon et al, ; Marti et al, ; NERC, ; Ngwira et al, ; Pulkkinen et al, ; Nikitina et al, ; Trichtchenko et al, ; Wei et al, ) relying on idealized models for broad regions of the Earth with structure that is simply depth dependent, one‐dimensional (e.g., Blum et al, ; Ferguson & Odwar, ; Fernberg, ). For such models, surface impedance has the symmetric form

Z_{1D} ((), f, x, y false| σ false(boldr false)) = ([], \begin{matrix} array 0 & array Z \\ array - Z & array 0 \end{matrix}) ((), f, x, y false| σ false(boldr false)),

for which ρ xy = ρ yx , and ρ xx = ρ yy = 0.…”

Section: Induction In the Conducting Earthmentioning

confidence: 99%

Extreme‐Value Geoelectric Amplitude and Polarization Across the Northeast United States

et al. 2019

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Maps are presented of extreme-value geoelectric field amplitude and horizontal polarization for the Northeast United States. These maps are derived from geoelectric time series calculated for sites across the Northeast by frequency-domain multiplication (time-domain convolution) of 172 magnetotelluric impedance tensors, acquired during a survey, with decades-long, 1-min resolution time series of geomagnetic variation, acquired at three magnetic observatories. The maps show that, during intense magnetic storms, high geoelectric amplitude hazards are realized across electrically resistive, igneous and metamorphic rock of the Appalachian Mountains and the New England Highlands, while low geoelectric hazards are realized across electrically conductive, sedimentary rock of the Appalachian Plateau and the Mid-Atlantic Coastal Plain. From statistical extrapolation, once-per-century (100-year) geoelectric amplitudes are highest at a site in Virginia at 25.44 V/km (followed by a site in Maine at 21.75 V/km and a site in Connecticut at 19.39 V/km); 100-year geoelectric amplitude exceeds 10 V/km at 12 sites across the northeast; geoelectric amplitude is lowest at a site in Virginia at 0.05 V/km. Average errors for these values are estimated to be about 38%, or much less than the more than 2 orders of magnitude range seen in geoelectric amplitudes from one survey site to another across the northeast. It is noteworthy that geoelectric fields tend to be most (least) polarized at locations with high (low) geoelectric hazard. Furthermore, geoelectric fields over the Appalachians tend to be polarized southeast-to-northwest, or generally in a direction orthogonal to the southwest-to-northeast geological strike. Results reported here inform utility companies in projects for evaluating and managing the response of power grid systems to the deleterious effects of geomagnetic disturbance.

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Z_{1D} ((), f, x, y false| σ false(boldr false)) = ([], \begin{matrix} array 0 & array Z \\ array - Z & array 0 \end{matrix}) ((), f, x, y false| σ false(boldr false)),

for which ρ xy = ρ yx , and ρ xx = ρ yy = 0.…”

Section: Induction In the Conducting Earthmentioning

confidence: 99%

Extreme‐Value Geoelectric Amplitude and Polarization Across the Northeast United States

et al. 2019

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“…In light of Figure , we do not use 1‐D surface impedance tensors derived from simple depth‐dependent models of Earth conductivity. 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, ).…”

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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“…We assume a layered Earth conductivity structure defined by the so‐called Quebec profile published by Boteler et al (). Admittedly, Quebec is far away from Hermanus, but models are similar below about depth 100 km corresponding to fluctuations with periods of 1 min and longer (Trichtchenko et al, ).…”

Section: Data Sets Utilizedmentioning

confidence: 99%

Extreme Value Analysis of Induced Geoelectric Field in South Africa

Lotz

Danskin

2017

Space Weather

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Extreme geomagnetic disturbances occur rarely but can have great impact on technological systems such as power supply networks. Long‐term planning for extreme events requires the estimation of event impact for occurrence periods greater than the length of observed data. With this in mind an analysis of extreme geomagnetic events observed in South Africa (middle geomagnetic latitude) is performed over four solar cycles (1974–2015). An algorithm to identify active periods with minimum SYM‐H ≤−100 nT is demonstrated. The sum of induced electric field over the course of each event is used to characterize the severity of each active period. It is found that the severity index (accumulated electric field magnitude ΣE) shares a highly linear relationship with accumulated SYM‐H over each event. The index ΣE is lognormal distributed, with tail deviating greater than lognormal, confirming heavy‐tailed occurrence. A general Pareto distribution is fitted to the tail of the distribution and extrapolated to calculate the return levels of extreme events. Return levels of once in 100 and once in 200 year events are estimated to be 9.4 × 104 mV/km min and 1.09 × 105 mV/km min, respectively. The top three events, in ascending order of severity, are the March 1989 storm, the events of late October 2003, and the April 1994 event—a long interval of coronal‐hole driven disturbances, bookended by two intense geomagnetic storms.

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Geoelectric field modelling for canadian space weather services

Cited by 3 publications

References 0 publications

Extreme‐Value Geoelectric Amplitude and Polarization Across the Northeast United States

Extreme‐Value Geoelectric Amplitude and Polarization Across the Northeast United States

Geoelectric Hazard Maps for the Pacific Northwest

Extreme Value Analysis of Induced Geoelectric Field in South Africa

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