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| Titel |
Double layers in the downward current region of the aurora |
| VerfasserIn |
R. E. Ergun, L. Andersson, C. W. Carlson, D. L. Newman, M. V. Goldman |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1023-5809
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| Digitales Dokument |
URL |
| Erschienen |
In: Nonlinear Processes in Geophysics ; 10, no. 1/2 ; Nr. 10, no. 1/2, S.45-52 |
| Datensatznummer |
250007819
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| Publikation (Nr.) |
 copernicus.org/npg-10-45-2003.pdf |
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| Zusammenfassung |
| 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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