Co-variation of nightglow emission from the O 2( A3Σ u+) and O 2( c1Σ u−) states and the oxygen green line, observed with the Keck I/II telescopes

Abstract

Sky spectra from the Keck I and II telescopes on Mauna Kea, Hawai′i reveal the terrestrial nightglow in unprecedented detail. We have recently demonstrated that the O 2( c 1Σ u −) state, the upper state of the O 2( c– X) Herzberg II bands, also radiates in a new transition, the O 2( c– b) system. The c– b bands, by their spectroscopic nature, present a more distinct atmospheric signature than the c– X bands. The question often arises as to whether the three O 2 Herzberg states should be considered a single coupled system or if they react in an independent manner. Particularly relevant is the issue of the mechanism of mesosphere/lower thermosphere oxygen green line production, the current belief being that it is the result of electronic energy transfer from the O 2( c) state to oxygen atoms. With the aid of Keck data from the HIRES and the ESI echelle spectrographs it is possible to address these questions. In the 410– 440 nm region there is relatively strong emission from the Herzberg I ( A– X) system and the new c– b system. We present data from March and October, 2000, showing the co-variation of these emissions, and how they correlate with the green line intensity.