Other
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmsm32b..09e&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #SM32B-09
Other
2704 Auroral Phenomena (2407), 2712 Electric Fields (2411), 2716 Energetic Particles, Precipitating, 2736 Magnetosphere/Ionosphere Interactions
Scientific paper
We report direct measurements of parallel electric fields, electron distributions, and ion distributions related to particle acceleration in the downward current region of the aurora. The observations suggest three distinct, narrowly-confined regions along the magnetic field (B) that are related to a strong double layer. In the "ramp" region, the parallel electric fields are hundreds of millivolts per meter and indicate a monotonic potential ramp localized to ~10 Debye lengths along B. On the high-potential side of the ramp, an unstable electron beam is seen for roughly another ~10 Debye lengths along B. In this "beam" region, the characteristic energy of the electrons matches the potential of the ramp. The electron beam is rapidly stabilized in a region with intense electrostatic waves and nonlinear structures interpreted as electron phase-space holes. The region of electrostatic turbulence is spatially separated from the ramp by the beam region. The parallel electric field structures are observed to move along B in the same direction as the accelerated electrons at roughly the ion-acoustic speed. Numerical simulations reproduce similar spatial makeup, electrostatic structure, and plasma characteristics of 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 associated with the generation of large-amplitude electron phase-space holes and plasma waves.
Andersson L.-L.
Carlson Carl W.
Ergun Robert E.
Goldman Martin V.
McFadden James P.
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