Abstract
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.