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Ion Anisotropy in Earth's Magnetotail: Importance of High‐Energy Ions.

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Title: Ion Anisotropy in Earth's Magnetotail: Importance of High‐Energy Ions.
Authors: Shi, Xiaofei1 (AUTHOR) sxf1698@g.ucla.edu, Angelopoulos, Vassilis1 (AUTHOR), Richard, Louis2 (AUTHOR), Artemyev, Anton1,3 (AUTHOR)
Source: Journal of Geophysical Research. Space Physics. Jun2026, Vol. 131 Issue 6, p1-12. 12p.
Subject Terms: *Geomagnetism, Ions, Current sheets, Magnetotails, Fast ions, Plasma pressure, Plasma physics
Company/Entity: THEMIS (Artificial satellites)
Abstract: The reconfiguration of the magnetotail current sheet during substorms often includes the formation of a thin current sheet (TCS) with a strong magnetic field line tension force. This force cannot be balanced by isotropic plasma pressure gradients, and force balance in such a TCS requires ion anisotropy and/or agyrotropy of plasma pressure. A statistical investigation of these plasma properties in the magnetotail is challenging because a significant contribution to ion anisotropy or agyrotropy stems from the suprathermal ion population, which often has energies beyond the upper limit of electrostatic analyzer measurements. In this study, we compare ion measurements from Cluster, MMS, and THEMIS to investigate the ion anisotropy in the magnetotail current sheet. We show that the central region of the magnetotail is characterized by transverse anisotropy of suprathermal ions, whereas subthermal field‐aligned anisotropic ions populate the magnetotail current sheet boundaries. Our results indicate that different ion populations (subthermal, thermal, and suprathermal ions) exhibit distinct behaviors within the current sheet, showing that different combinations of these populations contribute differently to the stability of current sheets. Key Points: We collect ion measurements from multiple missions to statistically investigate ion pressure anisotropy in the magnetotail current sheetNear the equatorial plane, suprathermal ions contribute to the transverse anisotropyAt the current sheet boundaries, subthermal ions contribute to the field‐aligned anisotropy [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.)
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Header DbId: 8gh
DbLabel: GreenFILE
An: 194810992
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PubTypeId: academicJournal
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  Data: Ion Anisotropy in Earth's Magnetotail: Importance of High‐Energy Ions.
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  Data: <searchLink fieldCode="AR" term="%22Shi%2C+Xiaofei%22">Shi, Xiaofei</searchLink><relatesTo>1</relatesTo> (AUTHOR)<i> sxf1698@g.ucla.edu</i><br /><searchLink fieldCode="AR" term="%22Angelopoulos%2C+Vassilis%22">Angelopoulos, Vassilis</searchLink><relatesTo>1</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Richard%2C+Louis%22">Richard, Louis</searchLink><relatesTo>2</relatesTo> (AUTHOR)<br /><searchLink fieldCode="AR" term="%22Artemyev%2C+Anton%22">Artemyev, Anton</searchLink><relatesTo>1,3</relatesTo> (AUTHOR)
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  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, p1-12. 12p.
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  Data: *<searchLink fieldCode="DE" term="%22Geomagnetism%22">Geomagnetism</searchLink><br /><searchLink fieldCode="DE" term="%22Ions%22">Ions</searchLink><br /><searchLink fieldCode="DE" term="%22Current+sheets%22">Current sheets</searchLink><br /><searchLink fieldCode="DE" term="%22Magnetotails%22">Magnetotails</searchLink><br /><searchLink fieldCode="DE" term="%22Fast+ions%22">Fast ions</searchLink><br /><searchLink fieldCode="DE" term="%22Plasma+pressure%22">Plasma pressure</searchLink><br /><searchLink fieldCode="DE" term="%22Plasma+physics%22">Plasma physics</searchLink>
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  Data: The reconfiguration of the magnetotail current sheet during substorms often includes the formation of a thin current sheet (TCS) with a strong magnetic field line tension force. This force cannot be balanced by isotropic plasma pressure gradients, and force balance in such a TCS requires ion anisotropy and/or agyrotropy of plasma pressure. A statistical investigation of these plasma properties in the magnetotail is challenging because a significant contribution to ion anisotropy or agyrotropy stems from the suprathermal ion population, which often has energies beyond the upper limit of electrostatic analyzer measurements. In this study, we compare ion measurements from Cluster, MMS, and THEMIS to investigate the ion anisotropy in the magnetotail current sheet. We show that the central region of the magnetotail is characterized by transverse anisotropy of suprathermal ions, whereas subthermal field‐aligned anisotropic ions populate the magnetotail current sheet boundaries. Our results indicate that different ion populations (subthermal, thermal, and suprathermal ions) exhibit distinct behaviors within the current sheet, showing that different combinations of these populations contribute differently to the stability of current sheets. Key Points: We collect ion measurements from multiple missions to statistically investigate ion pressure anisotropy in the magnetotail current sheetNear the equatorial plane, suprathermal ions contribute to the transverse anisotropyAt the current sheet boundaries, subthermal ions contribute to the field‐aligned anisotropy [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:
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    Identifiers:
      – Type: doi
        Value: 10.1029/2026JA035223
    Languages:
      – Code: eng
        Text: English
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      Pagination:
        PageCount: 12
        StartPage: 1
    Subjects:
      – SubjectFull: Geomagnetism
        Type: general
      – SubjectFull: Ions
        Type: general
      – SubjectFull: Current sheets
        Type: general
      – SubjectFull: Magnetotails
        Type: general
      – SubjectFull: Fast ions
        Type: general
      – SubjectFull: Plasma pressure
        Type: general
      – SubjectFull: Plasma physics
        Type: general
      – SubjectFull: THEMIS (Artificial satellites)
        Type: general
    Titles:
      – TitleFull: Ion Anisotropy in Earth's Magnetotail: Importance of High‐Energy Ions.
        Type: main
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          Name:
            NameFull: Shi, Xiaofei
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            NameFull: Angelopoulos, Vassilis
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            NameFull: Richard, Louis
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            NameFull: Artemyev, Anton
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            – D: 01
              M: 06
              Text: Jun2026
              Type: published
              Y: 2026
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              Value: 131
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              Value: 6
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            – TitleFull: Journal of Geophysical Research. Space Physics
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