N-2 TRIPLET BAND SYSTEMS AND ATOMIC OXYGEN IN THE DAYGLOW

New spectrographic observations of the Earth's dayglow have been acqui red by the Arizona Airglow Experiment (GLO) flown on the space shuttle . GLO is an imaging spectrograph that records simultaneous vertical pr ofiles of prominent Earth limb emissions occurring at wavelengths betw een 115 and 900 nm. This study addresses the measured emissions from t he N-2 triplet states (first positive, second positive, and Vegard-Kap lan band systems) and their excitation by the local photoelectron flux . The triplet state population distributions modeled for aurora by Car twright [1978] are modified for dayglow conditions by changing to a ph otoelectron-flux energy distribution and including resonance scatterin g by the first positive system. Modeled and observed intensities are i n excellent agreement, in contrast to the well-studied auroral case. T his work concentrates on dayglow conditions at 200 km altitude near th e subsolar point. Parameters to infer the local photoelectron flux fro m the emission band intensities are provided. Several atomic oxygen da yglow emission features were analyzed to complement the N-2 analysis. The photoelectron-excited O I(135.6, 777.4 nm) lines were found to be 3 to 4 times weaker than predicted while the O I(630.0, 844.6 nm) line s were in close agreement with the model prediction.