Spectrum of sprite halos

Abstract

[1] Spectra of sprite halos in the spectral ranges 200–500 nm and 640–1065 nm are calculated for different spectral resolutions (between 2 nm and 10 nm), rotational temperatures (220 K and 1000 K) and observation altitudes corresponding to mountain (3 km and 4.3 km), airplane (14 km), balloon (35 km) and space observation platforms. We have calculated the non-equilibrium vibrational distribution functions (VDF) of different excited electronic states of molecular nitrogen (N2) associated to sprite halo optical emissions in the ultraviolet (UV), due to the N2 Lyman-Birge-Hopfield (LBH) and Vegard-Kaplan (VK) band systems, and near UV, visible and near infrared (NIR) due to the first (1PG) and second positive (2PG) bands of N2. Comparison of synthetic sprite halo spectra with the single sprite halo spectrum existing to date shows reasonable agreement after the observed sprite halo spectra was corrected for instrument sensitivity response. Calculated VDFs of the N2(B3Πg) and N2(C3Πu) states of sprite halos show that the blue and NIR emissions produced through strong N2-1PG (B3Πg → A3Σu+) and N2-2PG (C3Πu → B3Πg) transitions are generally similar to those of known sprite spectral emission patterns, but differences may be observable at some vibrational levels. The calculated sprite halo spectra can be used as a predictive tool for the expected spectral emissions of sprite halos in different possible scenarios.