Rocket observations of the ultraviolet airglow during morning twilight

Abstract

The nitric oxide γ and δ bands, O II λ2470‐, O I λλ356‐ and 1304‐Å lines, and N2 Lyman‐Birge‐Hopfield and O2 Herzberg band emissions were observed during morning twilight between 90 and 246 km on September 24, 1979, with two rocket‐borne scanning monochromators viewing successively at 82° and 90° to the zenith near the sun‐earth‐rocket plane. The solar zenith angle was 110°. The relative intensitites of the two nitric oxide band systems suggest that the observed emission is primarily due to resonance fluorescence along the sunlit portion of the rocket line of sight, with the chemiluminescence contribution being greatly reduced from that observed during evening twilight. The densities at 200 km derived from the observed emission rates are 4×105 cm−3 for NO and 5×106 cm−3 for N(4S), consistent with recent odd nitrogen models which predict a much greater nighttime decrease of N(4S) than of NO. The atomic and ionic oxygen emissions are modeled in a self‐consistent way based on direct photoionization and photoelectron impact ionization. The atomic oxygen density near 100 km is derived from O2 Herzberg I band emission observed near the end of the flight.