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Nonlinear Evolution of Auroral Fine Structures Through the Feedback Instability in a Dipole Field Configuration.

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Title: Nonlinear Evolution of Auroral Fine Structures Through the Feedback Instability in a Dipole Field Configuration.
Authors: Sakaki, T.1 (AUTHOR) sakaki@p.phys.nagoya-u.ac.jp, Watanabe, T.‐H.1 (AUTHOR)
Source: Journal of Geophysical Research. Space Physics. Jun2026, Vol. 131 Issue 6, p1-13. 13p.
Subject Terms: *Geomagnetism, Magnetohydrodynamics, Magnetospheric physics, Plasma stability, Turbulence, Vortex methods
Abstract: Nonlinear simulations of the feedback instability in the Alfvénic magnetosphere‐ionosphere (M‐I) coupling system have been carried out by means of the reduced magnetohydrodynamic (MHD) equations with spatially non‐uniform kinematic viscosity and resistivity, coupled with two‐fluid equations, in order to investigate auroral fine‐structure formation in the dipole magnetic field. Spontaneous formation of vortex structures due to the secondary instability, followed by transition into turbulence, has been successfully reproduced. Collapse of the discrete auroral structures is accompanied by latitudinal expansion of turbulent fluctuations. The spatial scale and rotational sense of the vortex structures are consistent with those of auroral curls, and the energy spectrum of magnetospheric fluctuations in the turbulent state roughly follows the −5/3 ${-}5/3$‐law, and is consistent with the FAST spacecraft observation and the MHD turbulence theory. Key Points: Spontaneous formation of auroral fine structures through the feedback instability is successfully reproduced in a dipole magnetic fieldIonospheric density enhancements are distorted in the counterclockwise direction due to vorticity fluctuationsPower spectrum of the Alfvénic fluctuations in the magnetosphere roughly follows the −5/3 ${-}5/3$ law in the inertial subrange [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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  Data: Nonlinear Evolution of Auroral Fine Structures Through the Feedback Instability in a Dipole Field Configuration.
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  Data: <searchLink fieldCode="AR" term="%22Sakaki%2C+T%2E%22">Sakaki, T.</searchLink><relatesTo>1</relatesTo> (AUTHOR)<i> sakaki@p.phys.nagoya-u.ac.jp</i><br /><searchLink fieldCode="AR" term="%22Watanabe%2C+T%2E‐H%2E%22">Watanabe, T.‐H.</searchLink><relatesTo>1</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, p1-13. 13p.
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  Data: *<searchLink fieldCode="DE" term="%22Geomagnetism%22">Geomagnetism</searchLink><br /><searchLink fieldCode="DE" term="%22Magnetohydrodynamics%22">Magnetohydrodynamics</searchLink><br /><searchLink fieldCode="DE" term="%22Magnetospheric+physics%22">Magnetospheric physics</searchLink><br /><searchLink fieldCode="DE" term="%22Plasma+stability%22">Plasma stability</searchLink><br /><searchLink fieldCode="DE" term="%22Turbulence%22">Turbulence</searchLink><br /><searchLink fieldCode="DE" term="%22Vortex+methods%22">Vortex methods</searchLink>
– Name: Abstract
  Label: Abstract
  Group: Ab
  Data: Nonlinear simulations of the feedback instability in the Alfvénic magnetosphere‐ionosphere (M‐I) coupling system have been carried out by means of the reduced magnetohydrodynamic (MHD) equations with spatially non‐uniform kinematic viscosity and resistivity, coupled with two‐fluid equations, in order to investigate auroral fine‐structure formation in the dipole magnetic field. Spontaneous formation of vortex structures due to the secondary instability, followed by transition into turbulence, has been successfully reproduced. Collapse of the discrete auroral structures is accompanied by latitudinal expansion of turbulent fluctuations. The spatial scale and rotational sense of the vortex structures are consistent with those of auroral curls, and the energy spectrum of magnetospheric fluctuations in the turbulent state roughly follows the −5/3 ${-}5/3$‐law, and is consistent with the FAST spacecraft observation and the MHD turbulence theory. Key Points: Spontaneous formation of auroral fine structures through the feedback instability is successfully reproduced in a dipole magnetic fieldIonospheric density enhancements are distorted in the counterclockwise direction due to vorticity fluctuationsPower spectrum of the Alfvénic fluctuations in the magnetosphere roughly follows the −5/3 ${-}5/3$ law in the inertial subrange [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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        Value: 10.1029/2025JA034812
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      – Code: eng
        Text: English
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        PageCount: 13
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      – SubjectFull: Geomagnetism
        Type: general
      – SubjectFull: Magnetohydrodynamics
        Type: general
      – SubjectFull: Magnetospheric physics
        Type: general
      – SubjectFull: Plasma stability
        Type: general
      – SubjectFull: Turbulence
        Type: general
      – SubjectFull: Vortex methods
        Type: general
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      – TitleFull: Nonlinear Evolution of Auroral Fine Structures Through the Feedback Instability in a Dipole Field Configuration.
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              M: 06
              Text: Jun2026
              Type: published
              Y: 2026
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