Spectroscopic evidence for suprathermal electrons in enhanced auroras

Details Spectroscopic evidence for suprathermal electrons in enhanced auroras Spectroscopic evidence for suprathermal electrons in enhanced auroras

Apr 1997

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997jgr...102.7501h&link_type=abstract

Journal of Geophysical Research, Volume 102, Issue A4, p. 7501-7508

Physics

6

Atmospheric Composition And Structure: Airglow And Aurora, Ionosphere: Particle Precipitation, Magnetospheric Physics: Auroral Phenomena, Magnetospheric Physics: Magnetosphere/Ionosphere Interactions

Scientific paper

Auroral arcs frequently exhibit bands of enhanced intensity along the bottom edge. These bands have sharp upper borders and are referred to as enhanced lower borders or auroral hems. They are thought to be related to thin layers of enhanced luminosity observed both in auroral arcs and in pulsating auroras. These anomalous distributions of intensity as a function of altitude are referred to collectively as enhanced aurora (EA) and are of interest because they suggest a more complex process for producing auroral ionization and luminosity than the collisional degradation of precipitating electrons. Spectra of eight auroral hems were obtained with an imaging spectrograph and showed consistently that within the hem, there is an enhanced ratio of N2 1st positive emissions (red) to N2+ 1st negative emissions (blue). The enhancement in the red/blue ratio ranged from 10% to 100%. There was a generally smaller and less consistent enhancement in the ratio of the O2+ 1st negative band at 5275 Å to the N2+ 1st negative. Observations of the far red spectra of several hems showed no enhancement in the ratio of N2 1st positive to N2+ Meinel emissions. There were no simultaneous measurements of the Meinel and the N2+ 1st negatives. It is argued that the enhanced spectral ratios are indicative of a population of suprathermal electrons with a sharp energy cutoff near the ionization potential of N2 and that the electrons are energized in situ through wave-particle interactions or possibly by dc electric fields. It is also noted that some but not all of the hems are type b red lower borders.

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