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Analysis and modeling of sprite green ghosts
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  • Hans Stenbaek-Nielsen,
  • Thomas Ashcraft,
  • Matthew McHarg,
  • Jacob Harley
Hans Stenbaek-Nielsen
Univ. of Alaska Fairbanks

Corresponding Author:hcnielsen@alaska.edu

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Thomas Ashcraft
Heliotown Observatory
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Matthew McHarg
United States Air Force Academy
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Jacob Harley
US Air Force Academy
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In 2019 sprite observations appeared on You-Tube showing green emissions in the top of some sprites and after the main sprite. The emissions were named green ghosts. We present here similar color camera observations made on 24 and 25 May 2020 from Lamy, NM. The recordings were made at 30 fps. The green ghost increased in brightness for 3 to 4 frames after the main ‘jellyfish’ sprite and decayed thereafter. The delayed green emissions are likely from atomic oxygen at 557.7 nm, the auroral green line, which is a forbidden atomic oxygen emission with a radiative life time of 0.7 s. In the atmosphere the emissions are affected by quenching and at the altitude of the green ghost the decay time constant is substantially less. We suggest that the green ghost is generated by super thermal electrons exciting ambient atomic oxygen (only 4.1 eV required). The electrons are energized by the large-scale sprite electric field, which initially caused the sprite, and decays over some time after the sprite. We present a simple model based on this idea. The model assumes an exponentially decaying sprite E-field and reproduces the observed delayed peak in the green emissions and the subsequent decay of the emissions.