Modeling studies of NO‐γ emissions of sprites

Abstract

Motivated by observations of NO‐γ emissions: NO(A2Σ+) → NO(X2Πr) + hν from streamer discharges in laboratory experiments, we develop a model to study these emissions associated with streamer discharges in air at different pressures. The modeling results indicate that the NO(A2Σ+) species in sprite streamers at 70 km altitude are mostly produced by interaction of N2(A3Σu+) metastable species with high‐density ambient NO(X2Πr) molecules. Analysis of the production and loss mechanisms for the upper excited states leading to NO‐γ and N2 LBH emissions demonstrates that the total intensity of NO‐γ emissions associated with sprites is substantially weaker than that of the N2 LBH emissions. The same conclusion can be drawn for elves following similar analysis. It is demonstrated that the presented modeling approach and analysis are consistent with prior knowledge on NO‐γ emissions from aurora, indicating that to observe the NO‐γ emissions from aurora, the ambient NO density must be highly enhanced in the auroral region.