Magnetotail Source of Premidnight Upward Field‐Aligned Currents: Nature of the Substorm Current System.
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| Title: | Magnetotail Source of Premidnight Upward Field‐Aligned Currents: Nature of the Substorm Current System. |
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| Authors: | Nagai, Tsugunobu1 (AUTHOR) nagai@stp.isas.jaxa.jp, Shinohara, Iku2 (AUTHOR) |
| Source: | Journal of Geophysical Research. Space Physics. Jun2026, Vol. 131 Issue 6, p1-20. 20p. |
| Subject Terms: | *Ionosphere, Magnetotails, Magnetic reconnection, Electric currents, Magnetospheric physics |
| Abstract: | The substorm current wedge constitutes the backbone of the substorm current system. Its field‐aligned current components include an upward current in the premidnight sector and a downward current in the midnight‐morning sector, which connect the auroral ionosphere to the magnetotail. Because the fundamental ionospheric manifestations of magnetospheric substorms are dynamic auroral activity and the westward electrojet, the properties of these field‐aligned currents provide key insights into magnetotail dynamics during substorms. We investigate the structure of field‐aligned currents in the near‐Earth magnetotail at radial distances of 8–15 RE using Geotail observations during the formation of the substorm current wedge. The premidnight field‐aligned currents are located in the outermost plasma sheet and form a double‐sheet structure. In the double‐sheet structure, the outer earthward currents are carried by tailward‐flowing Hall electrons, whereas the inner tailward currents are carried by earthward‐flowing accelerated electrons. These electrons are accompanied by earthward‐flowing accelerated ions in the inner tailward current layer. The observed characteristics of the current sheet structure strongly suggest that the upward field‐aligned currents are directly driven by magnetic reconnection occurring in the near‐Earth magnetotail at radial distances of 20–30 RE. The midnight–morning downward field‐aligned currents are located in the outer plasma sheet and have a thick single‐sheet structure. Although these results are largely based on Geotail observations with limited observational capabilities from the current perspective, the long‐term magnetotail survey performed by Geotail provided a sufficient number of clear‐cut events to elucidate the underlying physical processes. Key Points: The premidnight field‐aligned currents at substorm onset are located in the outermost plasma sheet and exhibit a double‐sheet structureThe midnight–morning downward field‐aligned currents are located in the outer plasma sheet and form a thick single‐sheet structureThe premidnight upward field‐aligned currents are directly driven by magnetic reconnection occurring in the near‐Earth magnetotail [ABSTRACT FROM AUTHOR] |
| Copyright of Journal of Geophysical Research. Space Physics is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.) | |
| Database: | GreenFILE |
| FullText | Text: Availability: 0 |
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| Header | DbId: 8gh DbLabel: GreenFILE An: 194810989 AccessLevel: 6 PubType: Academic Journal PubTypeId: academicJournal PreciseRelevancyScore: 0 |
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| Items | – Name: Title Label: Title Group: Ti Data: Magnetotail Source of Premidnight Upward Field‐Aligned Currents: Nature of the Substorm Current System. – Name: Author Label: Authors Group: Au Data: <searchLink fieldCode="AR" term="%22Nagai%2C+Tsugunobu%22">Nagai, Tsugunobu</searchLink><relatesTo>1</relatesTo> (AUTHOR)<i> nagai@stp.isas.jaxa.jp</i><br /><searchLink fieldCode="AR" term="%22Shinohara%2C+Iku%22">Shinohara, Iku</searchLink><relatesTo>2</relatesTo> (AUTHOR) – Name: TitleSource Label: Source Group: Src Data: <searchLink fieldCode="JN" term="%22Journal+of+Geophysical+Research%2E+Space+Physics%22">Journal of Geophysical Research. Space Physics</searchLink>. Jun2026, Vol. 131 Issue 6, p1-20. 20p. – Name: Subject Label: Subject Terms Group: Su Data: *<searchLink fieldCode="DE" term="%22Ionosphere%22">Ionosphere</searchLink><br /><searchLink fieldCode="DE" term="%22Magnetotails%22">Magnetotails</searchLink><br /><searchLink fieldCode="DE" term="%22Magnetic+reconnection%22">Magnetic reconnection</searchLink><br /><searchLink fieldCode="DE" term="%22Electric+currents%22">Electric currents</searchLink><br /><searchLink fieldCode="DE" term="%22Magnetospheric+physics%22">Magnetospheric physics</searchLink> – Name: Abstract Label: Abstract Group: Ab Data: The substorm current wedge constitutes the backbone of the substorm current system. Its field‐aligned current components include an upward current in the premidnight sector and a downward current in the midnight‐morning sector, which connect the auroral ionosphere to the magnetotail. Because the fundamental ionospheric manifestations of magnetospheric substorms are dynamic auroral activity and the westward electrojet, the properties of these field‐aligned currents provide key insights into magnetotail dynamics during substorms. We investigate the structure of field‐aligned currents in the near‐Earth magnetotail at radial distances of 8–15 RE using Geotail observations during the formation of the substorm current wedge. The premidnight field‐aligned currents are located in the outermost plasma sheet and form a double‐sheet structure. In the double‐sheet structure, the outer earthward currents are carried by tailward‐flowing Hall electrons, whereas the inner tailward currents are carried by earthward‐flowing accelerated electrons. These electrons are accompanied by earthward‐flowing accelerated ions in the inner tailward current layer. The observed characteristics of the current sheet structure strongly suggest that the upward field‐aligned currents are directly driven by magnetic reconnection occurring in the near‐Earth magnetotail at radial distances of 20–30 RE. The midnight–morning downward field‐aligned currents are located in the outer plasma sheet and have a thick single‐sheet structure. Although these results are largely based on Geotail observations with limited observational capabilities from the current perspective, the long‐term magnetotail survey performed by Geotail provided a sufficient number of clear‐cut events to elucidate the underlying physical processes. Key Points: The premidnight field‐aligned currents at substorm onset are located in the outermost plasma sheet and exhibit a double‐sheet structureThe midnight–morning downward field‐aligned currents are located in the outer plasma sheet and form a thick single‐sheet structureThe premidnight upward field‐aligned currents are directly driven by magnetic reconnection occurring in the near‐Earth magnetotail [ABSTRACT FROM AUTHOR] – Name: AbstractSuppliedCopyright Label: Group: Ab Data: <i>Copyright of Journal of Geophysical Research. Space Physics is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.) |
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| RecordInfo | BibRecord: BibEntity: Identifiers: – Type: doi Value: 10.1029/2026JA035294 Languages: – Code: eng Text: English PhysicalDescription: Pagination: PageCount: 20 StartPage: 1 Subjects: – SubjectFull: Ionosphere Type: general – SubjectFull: Magnetotails Type: general – SubjectFull: Magnetic reconnection Type: general – SubjectFull: Electric currents Type: general – SubjectFull: Magnetospheric physics Type: general Titles: – TitleFull: Magnetotail Source of Premidnight Upward Field‐Aligned Currents: Nature of the Substorm Current System. Type: main BibRelationships: HasContributorRelationships: – PersonEntity: Name: NameFull: Nagai, Tsugunobu – PersonEntity: Name: NameFull: Shinohara, Iku IsPartOfRelationships: – BibEntity: Dates: – D: 01 M: 06 Text: Jun2026 Type: published Y: 2026 Identifiers: – Type: issn-print Value: 21699380 Numbering: – Type: volume Value: 131 – Type: issue Value: 6 Titles: – TitleFull: Journal of Geophysical Research. Space Physics Type: main |
| ResultId | 1 |
