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Optical Spectra of Small-scale Sprite Features Observed at 10,000 fps
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  • Hans C. Stenbaek-Nielsen,
  • Matthew G McHarg,
  • Ryan Haaland,
  • Alejandro Luque
Hans C. Stenbaek-Nielsen
University of Alaska Fairbanks

Corresponding Author:[email protected]

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Matthew G McHarg
US Air Force Academy
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Ryan Haaland
Augsburg College
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Alejandro Luque
Institute for Astrophysics of Andalusia (IAA-CSIC), in Granada, Spain
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Spectra of small-scale sprite structures, downward and upward propagating streamers, glow, and beads, were recorded with a slit-less spectrograph at 10,000 frames per second (fps) from aircraft missions in 2009 and 2013. The spectra are dominated by emissions from molecular nitrogen, the 1 positive band in the red, and in the blue the 2 positive band plus the 1 negative band of molecular nitrogen ions. The excitation threshold for the blue emissions is higher than for the red emissions so the blue/red ratio can, in principle, be used as a proxy for the electron energy leading to the emissions. We extracted for analysis time series of spectra from 11 sprites: 18 time series from downwards propagating streamers, 6 from upward propagating streamers, 14 from glow and 12 from beads. The total number of spectra in the 50 time series is 953. Blue emissions are almost exclusively associated with streamers indicating the more energetic nature of streamers compared with glow and beads. Both downward and upward propagating streamers start and end with low blue emissions indicating time variations in the associated processes. Because the red and blue nitrogen emissions are significantly affected by quenching, which is altitude dependent, and we do not have sufficiently accurate altitudes, the observed spectral blue/red ratios cannot be directly applied to sprite models.
27 Oct 2020Published in Journal of Geophysical Research: Atmospheres volume 125 issue 20. 10.1029/2020JD033170