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Nonlinear Processes in Geophysics An interactive open-access journal of the European Geosciences Union
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Volume 10, issue 1/2
Nonlin. Processes Geophys., 10, 45-52, 2003
https://doi.org/10.5194/npg-10-45-2003
© Author(s) 2003. This work is licensed under
the Creative Commons Attribution-NonCommercial-ShareAlike 2.5 License.

Special issue: 4th International Workshop on Nonlinear Waves and Chaos in...

Nonlin. Processes Geophys., 10, 45-52, 2003
https://doi.org/10.5194/npg-10-45-2003
© Author(s) 2003. This work is licensed under
the Creative Commons Attribution-NonCommercial-ShareAlike 2.5 License.

  30 Apr 2003

30 Apr 2003

Double layers in the downward current region of the aurora

R. E. Ergun1,2, L. Andersson2, C. W. Carlson3, D. L. Newman4, and M. V. Goldman4 R. E. Ergun et al.
  • 1Department of Astrophysical and Planetary Sciences, University of Colorado, Boulder, CO, USA
  • 2Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO, USA
  • 3Space Sciences Laboratory, University of California, Berkeley, CA, USA
  • 4Center for Integrated Plasma Studies, University of Colorado, Boulder, CO, USA

Abstract. Direct observations of magnetic-field-aligned (parallel) electric fields in the downward current region of the aurora provide decisive evidence of naturally occurring double layers. We report measurements of parallel electric fields, electron fluxes and ion fluxes related to double layers that are responsible for particle acceleration. The observations suggest that parallel electric fields organize into a structure of three distinct, narrowly-confined regions along the magnetic field (B). In the "ramp" region, the measured parallel electric field forms a nearly-monotonic potential ramp that is localized to ~ 10 Debye lengths along B. The ramp is moving parallel to B at the ion acoustic speed (vs) and in the same direction as the accelerated electrons. On the high-potential side of the ramp, in the "beam" region, an unstable electron beam is seen for roughly another 10 Debye lengths along B. The electron beam is rapidly stabilized by intense electrostatic waves and nonlinear structures interpreted as electron phase-space holes. The "wave" region is physically separated from the ramp by the beam region. Numerical simulations reproduce a similar ramp structure, beam region, electrostatic turbulence region and plasma characteristics as seen in the observations. These results suggest that large double layers can account for the parallel electric field in the downward current region and that intense electrostatic turbulence rapidly stabilizes the accelerated electron distributions. These results also demonstrate that parallel electric fields are directly associated with the generation of large-amplitude electron phase-space holes and plasma waves.

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