Emissions from the N2 Lyman-Birge-Hopfield bands in the earth's atmosphere

Abstract

Recent work on the N2 Lyman-Birge-Hopfield (LBH) band (a1Πg−X1Σg+) emissions from the Earth's aurora and daytime airglow has shown that models can give good agreement with observations by including cascading between the singlet (a1Πg, w1Δu and a′1Σu−) states. Both radiative and collision induced transitions contribute to the cascading. The collision induced transitions involve a process — sometimes referred to as collision-induced electronic transitions (CIET) — which has not been included in most models of the LBH bands from the Earth's atmosphere. Cascading not only improves the fit to the relative vibrational populations observed, it also increases the emission from the LBH bands, by a factor of ∼1.6 in the daytime airglow. Such an increase is consistent with recent work by Budzien et al. [1994] and Link et al. [1994]. In the aurora some calculations have included radiative cascading but not CIET, which is expected to be more important in typical auroras. However, the calculations involving CIET are based on extrapolation from laboratory measurements. These extrapolations are a source of significant uncertainty in the calculations.