Estimating ionospheric currents by inversion from ground-based geomagnetic data and calculating geoelectric fields for studies of geomagnetically induced currents

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dc.contributor.authorde Villiers, J S
dc.contributor.authorPirjola, R J
dc.contributor.authorCilliers, P J
dc.date.accessioned2021-10-08T07:04:01Z
dc.date.available2021-10-08T07:04:01Z
dc.date.issued2016
dc.description.abstractThis research focuses on the inversion of geomagnetic variation field measurements to obtain the source currents in the ionosphere and magnetosphere, and to determine the geoelectric fields at the Earth’s surface. During geomagnetic storms, the geoelectric fields create geomagnetically induced currents (GIC) in power networks. These GIC may disturb the operation of power systems, cause damage to power transformers, and even result in power blackouts. In this model, line currents running east–west along given latitudes are postulated to exist at a certain height above the Earth’s surface. This physical arrangement results in the fields on the ground being composed of a zero magnetic east component and a nonzero electric east component. The line current parameters are estimated by inverting Fourier integrals (over wavenumber) of elementary geomagnetic fields using the Levenberg–Marquardt technique. The output parameters of the model are the ionospheric current strength and the geoelectric east component at the Earth’s surface. A conductivity profile of the Earth is adapted from a shallow layered-Earth model for one observatory, together with a deep-layer model derived from satellite observations. This profile is used to obtain the ground surface impedance and therefore the reflection coefficient in the integrals. The inputs for the model are a spectrum of the geomagnetic data for 31 May 2013. The output parameters of the model are spectrums of the ionospheric current strength and of the surface geoelectric field. The inverse Fourier transforms of these spectra provide the time variations on the same day. The geoelectric field data can be used as a proxy for GIC in the prediction of GIC for power utilities. The current strength data can assist in the interpretation of upstream solar wind behaviour.
dc.identifier.apacitationde Villiers, J. S., Pirjola, R. J., & Cilliers, P. J. (2016). Estimating ionospheric currents by inversion from ground-based geomagnetic data and calculating geoelectric fields for studies of geomagnetically induced currents. <i>Earth, Planets and Space</i>, 68(1), 174 - 177. http://hdl.handle.net/11427/34410en_ZA
dc.identifier.chicagocitationde Villiers, J S, R J Pirjola, and P J Cilliers "Estimating ionospheric currents by inversion from ground-based geomagnetic data and calculating geoelectric fields for studies of geomagnetically induced currents." <i>Earth, Planets and Space</i> 68, 1. (2016): 174 - 177. http://hdl.handle.net/11427/34410en_ZA
dc.identifier.citationde Villiers, J.S., Pirjola, R.J. & Cilliers, P.J. 2016. Estimating ionospheric currents by inversion from ground-based geomagnetic data and calculating geoelectric fields for studies of geomagnetically induced currents. <i>Earth, Planets and Space.</i> 68(1):174 - 177. http://hdl.handle.net/11427/34410en_ZA
dc.identifier.issn1343-8832
dc.identifier.issn1880-5981
dc.identifier.ris TY - Journal Article AU - de Villiers, J S AU - Pirjola, R J AU - Cilliers, P J AB - This research focuses on the inversion of geomagnetic variation field measurements to obtain the source currents in the ionosphere and magnetosphere, and to determine the geoelectric fields at the Earth’s surface. During geomagnetic storms, the geoelectric fields create geomagnetically induced currents (GIC) in power networks. These GIC may disturb the operation of power systems, cause damage to power transformers, and even result in power blackouts. In this model, line currents running east–west along given latitudes are postulated to exist at a certain height above the Earth’s surface. This physical arrangement results in the fields on the ground being composed of a zero magnetic east component and a nonzero electric east component. The line current parameters are estimated by inverting Fourier integrals (over wavenumber) of elementary geomagnetic fields using the Levenberg–Marquardt technique. The output parameters of the model are the ionospheric current strength and the geoelectric east component at the Earth’s surface. A conductivity profile of the Earth is adapted from a shallow layered-Earth model for one observatory, together with a deep-layer model derived from satellite observations. This profile is used to obtain the ground surface impedance and therefore the reflection coefficient in the integrals. The inputs for the model are a spectrum of the geomagnetic data for 31 May 2013. The output parameters of the model are spectrums of the ionospheric current strength and of the surface geoelectric field. The inverse Fourier transforms of these spectra provide the time variations on the same day. The geoelectric field data can be used as a proxy for GIC in the prediction of GIC for power utilities. The current strength data can assist in the interpretation of upstream solar wind behaviour. DA - 2016 DB - OpenUCT DP - University of Cape Town IS - 1 J1 - Earth, Planets and Space LK - https://open.uct.ac.za PY - 2016 SM - 1343-8832 SM - 1880-5981 T1 - Estimating ionospheric currents by inversion from ground-based geomagnetic data and calculating geoelectric fields for studies of geomagnetically induced currents TI - Estimating ionospheric currents by inversion from ground-based geomagnetic data and calculating geoelectric fields for studies of geomagnetically induced currents UR - http://hdl.handle.net/11427/34410 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/34410
dc.identifier.vancouvercitationde Villiers JS, Pirjola RJ, Cilliers PJ. Estimating ionospheric currents by inversion from ground-based geomagnetic data and calculating geoelectric fields for studies of geomagnetically induced currents. Earth, Planets and Space. 2016;68(1):174 - 177. http://hdl.handle.net/11427/34410.en_ZA
dc.language.isoeng
dc.publisher.departmentDepartment of Chemical Engineering
dc.publisher.facultyFaculty of Engineering and the Built Environment
dc.sourceEarth, Planets and Space
dc.source.journalissue1
dc.source.journalvolume68
dc.source.pagination174 - 177
dc.source.urihttps://dx.doi.org/10.1186/s40623-016-0530-1
dc.subject.otherGeomagnetic induced currents
dc.subject.otherGeoelectric fields and currents
dc.subject.otherInversion
dc.subject.otherModelling
dc.titleEstimating ionospheric currents by inversion from ground-based geomagnetic data and calculating geoelectric fields for studies of geomagnetically induced currents
dc.typeJournal Article
uct.type.publicationResearch
uct.type.resourceJournal Article
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