Physics
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufmsm12a0475m&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #SM12A-0475
Physics
2451 Particle Acceleration, 2704 Auroral Phenomena (2407), 2712 Electric Fields (2411), 2736 Magnetosphere/Ionosphere Interactions, 2794 Instruments And Techniques
Scientific paper
Recent observations and simulations have shown that the auroral acceleration region is primarily confined to altitudes below ~3 Re geocentric, and that a significant portion of the potential drop is often confined to a strong double layer at the lower edge. This double layer acts to accelerate cold ionospheric ions into a beam, reducing the ion density to approximately that of the energetic auroral electron beam. In addition, the double layer reflects most of the up-going scattered primary and secondary electrons created when the primary electrons interact with the upper atmosphere. The magnitude of this strong double layer adjusts to a level that produces charge neutrality within the density cavity. This strong double layer typically contains 30%-50% of the potential drop, however at times the double layer potential is reduced to 10% or less of the total potential. These periods are observed when a population of trapped electrons is present within the density cavity. This paper will present FAST observations of this phenomena and discuss how trapped electrons can affect the potential distribution within auroral arcs. In addition we will discuss a technique that may allow a determination of the distribution of potential along auroral flux tubes based upon single spacecraft measurements of particle distributions. The technique involves identifying the population of field-aligned electrons that result from photo-ionization of geocoronal hydrogen within the acceleration region. Since the spectra of these photo-electrons depends upon the distribution of electric field, an inversion of the spectra can be used to find the potential distribution. Examples from FAST that show this population will be presented along with preliminary attempts at inversion.
Carlson Carl W.
Ergun Robert E.
McFadden James P.
Temerin Michael
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