Nowcasting and Validating Earth's Electric Field Response to Extreme Space Weather Events Using Magnetotelluric Data: Application to the September 2017 Geomagnetic Storm and Comparison to Observed and Modeled Fields in Scotland
Abstract In the United Kingdom, geomagnetically induced currents (GICs) are calculated from thin‐sheet electrical conductivity models. In the absence of conductivity models, time derivatives of magnetic fields are sometimes used as proxies for GIC‐related electric fields. An alternative approach, fa...
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| Format: | Article |
| Language: | English |
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Wiley
2021-01-01
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| Series: | Space Weather |
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| Online Access: | https://doi.org/10.1029/2019SW002432 |
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| _version_ | 1841536527344074752 |
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| author | Fiona Simpson Karsten Bahr |
| author_facet | Fiona Simpson Karsten Bahr |
| author_sort | Fiona Simpson |
| collection | DOAJ |
| description | Abstract In the United Kingdom, geomagnetically induced currents (GICs) are calculated from thin‐sheet electrical conductivity models. In the absence of conductivity models, time derivatives of magnetic fields are sometimes used as proxies for GIC‐related electric fields. An alternative approach, favored in the United States, is to calculate storm time electric fields from time‐independent impedance tensors computed from an array of magnetotelluric (MT) sites and storm time magnetic fields recorded at geomagnetic observatories or assumed from line current models. A paucity of direct measurements of storm time electric fields has restricted validation of these different techniques for nowcasting electric fields and GICs. Here, we present unique storm time electric field data from seven MT sites in Scotland that recorded before, during, and after the September 2017 magnetic storm. By Fourier transforming electric field spectra computed using different techniques back to the time domain, we are able to make direct comparisons with these measured storm time electric field time series. This enables us to test the validity of different approaches to nowcasting electric fields. Our preferred technique involves frequency domain multiplication of magnetic field spectra from a regional site with a local impedance tensor that has been corrected for horizontal magnetic field gradients present between the local site and the regional site using perturbation tensors derived from geomagnetic depth sounding (GDS). Scatter plots of scaling factors between measured and nowcasted electric fields demonstrate the importance of coupling between the polarization of the storm time magnetic source field and Earth's direction‐dependent deep electrical conductivity structure. |
| format | Article |
| id | doaj-art-f0c932c285664995b3aaec4a1931b621 |
| institution | Kabale University |
| issn | 1542-7390 |
| language | English |
| publishDate | 2021-01-01 |
| publisher | Wiley |
| record_format | Article |
| series | Space Weather |
| spelling | doaj-art-f0c932c285664995b3aaec4a1931b6212025-01-14T16:27:00ZengWileySpace Weather1542-73902021-01-01191n/an/a10.1029/2019SW002432Nowcasting and Validating Earth's Electric Field Response to Extreme Space Weather Events Using Magnetotelluric Data: Application to the September 2017 Geomagnetic Storm and Comparison to Observed and Modeled Fields in ScotlandFiona Simpson0Karsten Bahr1School of Ocean and Earth Science University of Southampton Southampton UKInstitut für Geophysik Georg‐August Universität Göttingen GermanyAbstract In the United Kingdom, geomagnetically induced currents (GICs) are calculated from thin‐sheet electrical conductivity models. In the absence of conductivity models, time derivatives of magnetic fields are sometimes used as proxies for GIC‐related electric fields. An alternative approach, favored in the United States, is to calculate storm time electric fields from time‐independent impedance tensors computed from an array of magnetotelluric (MT) sites and storm time magnetic fields recorded at geomagnetic observatories or assumed from line current models. A paucity of direct measurements of storm time electric fields has restricted validation of these different techniques for nowcasting electric fields and GICs. Here, we present unique storm time electric field data from seven MT sites in Scotland that recorded before, during, and after the September 2017 magnetic storm. By Fourier transforming electric field spectra computed using different techniques back to the time domain, we are able to make direct comparisons with these measured storm time electric field time series. This enables us to test the validity of different approaches to nowcasting electric fields. Our preferred technique involves frequency domain multiplication of magnetic field spectra from a regional site with a local impedance tensor that has been corrected for horizontal magnetic field gradients present between the local site and the regional site using perturbation tensors derived from geomagnetic depth sounding (GDS). Scatter plots of scaling factors between measured and nowcasted electric fields demonstrate the importance of coupling between the polarization of the storm time magnetic source field and Earth's direction‐dependent deep electrical conductivity structure.https://doi.org/10.1029/2019SW002432space weatherelectromagnetic inductionnowcastinggeomagnetically induced currentsSeptember 2017 magnetic storm |
| spellingShingle | Fiona Simpson Karsten Bahr Nowcasting and Validating Earth's Electric Field Response to Extreme Space Weather Events Using Magnetotelluric Data: Application to the September 2017 Geomagnetic Storm and Comparison to Observed and Modeled Fields in Scotland Space Weather space weather electromagnetic induction nowcasting geomagnetically induced currents September 2017 magnetic storm |
| title | Nowcasting and Validating Earth's Electric Field Response to Extreme Space Weather Events Using Magnetotelluric Data: Application to the September 2017 Geomagnetic Storm and Comparison to Observed and Modeled Fields in Scotland |
| title_full | Nowcasting and Validating Earth's Electric Field Response to Extreme Space Weather Events Using Magnetotelluric Data: Application to the September 2017 Geomagnetic Storm and Comparison to Observed and Modeled Fields in Scotland |
| title_fullStr | Nowcasting and Validating Earth's Electric Field Response to Extreme Space Weather Events Using Magnetotelluric Data: Application to the September 2017 Geomagnetic Storm and Comparison to Observed and Modeled Fields in Scotland |
| title_full_unstemmed | Nowcasting and Validating Earth's Electric Field Response to Extreme Space Weather Events Using Magnetotelluric Data: Application to the September 2017 Geomagnetic Storm and Comparison to Observed and Modeled Fields in Scotland |
| title_short | Nowcasting and Validating Earth's Electric Field Response to Extreme Space Weather Events Using Magnetotelluric Data: Application to the September 2017 Geomagnetic Storm and Comparison to Observed and Modeled Fields in Scotland |
| title_sort | nowcasting and validating earth s electric field response to extreme space weather events using magnetotelluric data application to the september 2017 geomagnetic storm and comparison to observed and modeled fields in scotland |
| topic | space weather electromagnetic induction nowcasting geomagnetically induced currents September 2017 magnetic storm |
| url | https://doi.org/10.1029/2019SW002432 |
| work_keys_str_mv | AT fionasimpson nowcastingandvalidatingearthselectricfieldresponsetoextremespaceweathereventsusingmagnetotelluricdataapplicationtotheseptember2017geomagneticstormandcomparisontoobservedandmodeledfieldsinscotland AT karstenbahr nowcastingandvalidatingearthselectricfieldresponsetoextremespaceweathereventsusingmagnetotelluricdataapplicationtotheseptember2017geomagneticstormandcomparisontoobservedandmodeledfieldsinscotland |