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TitleEvaluating the impact of earth transfer function on the geoelectric field for GIC modelling
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AuthorTinel, M; Boteler, D; Trichtchenko, L
SourceGeological Survey of Canada, Open File 8074, 2016, 76 pages, https://doi.org/10.4095/298818
Year2016
PublisherNatural Resources Canada
Documentopen file
Lang.English
Mediaon-line; digital
File formatpdf
Subjectsgeophysics; geoelectric variations; geomagnetism; geomagnetic fields; geomagnetic variations; electric power; remote sensing
Illustrationsplots; graphs; tables; histograms
ProgramNorthern Canada Geohazards Project, Public Safety Geoscience
Released2016 06 30
Abstract(Summary)
Geomagnetic disturbances that occur as a result of solar activity create electric fields that affect power systems on the surface of the Earth. The effect on the power system depends on the size of the surface electric field, which depends on the conductivity structure of the Earth in the area of the power system. To assess the geomagnetic hazard to power systems Earth conductivity models have been produced for different geological regions across Canada. This study examines how uncertainties in the Earth model affect the calculated electric fields. All of the Earth conductivity models tested in this report are related to a one-dimensional Earth model composed of several layers of different characteristics. The conductivity models tested are variations where each layer property is always within a range of possible values. The purpose of this was to determine the effect of conductive and resistive Earth layer combinations on the surface impedance, which is used to calculate the surface electric field. In general, a more resistive Earth creates a higher surface Earth response. It was found in a basic test Earth model that, within two uniform Earth models with different conductivities which produce a specific Earth transfer function response; there are some conductivity combinations that can produce even greater Earth transfer function amplitudes. This idea was applied to an artificial geomagnetic field, in order to determine a theoretical electric field. It was found that it is possible to find an Earth structure model to maximize the Earth transfer function amplitude at different frequencies, and consequently the electric field amplitudes in the frequency and time domain. The same procedure of changing the conductivities of individual layers was applied to the Quebec Earth model. Using geomagnetic field measured during different days at the Ottawa Magnetic Observatory, it was again possible to determine the earth model that gave the highest electric field amplitude in the time domain. It was discovered that the particular maximum Earth model is specific to the frequency content of the geomagnetic field, which is different for each geomagnetic storm. In some cases the difference between the maximized electric field amplitude and highest amplitude of the electric field due to the highest resistivity model would be significant. This would mean that the combinations within an Earth model with some uncertainties cannot be neglected, even if determining the absolute highest electric field for a particular geomagnetic storm is not straight forward. However, more analysis of the electric field amplitudes shows that in the general case, the highest electric field values can be estimated by the Earth model with the highest resistivities.
Summary(Plain Language Summary, not published)
Space weather refers to the dynamic conditions on the Sun and in the space environment, in particular, in the near-Earth environment, that can affect critical infrastructure. NRCan operates the Canadian Space Weather Forecast Centre and conducts research into space weather effects on power systems, pipelines, radio communications and GNSS positioning to help Canadian industry understand and mitigate the effects of space weather. The effect on the power system depends on the size of the surface electric field, which depends on the earth conductivity structure. To assess the geomagnetic hazard to power systems, Earth conductivity models have been produced for different geological regions across Canada. This study examines how uncertainties in the Earth model affect the calculated electric fields.
GEOSCAN ID298818