Studies of the Terrestrial Atmosphere

Sri International, Menlo Park CA

Investigators

Abstract

This project combines observational and laboratory investigations of mesospheric and thermospheric oxygen chemistry. The first task is elucidation of the chemical mechanism that is responsible for the large variability in the sodium D2/D1 line ratio in the nightglow. Although a newly recognized phenomenon, it is now evident from repeated measurements in different locations and environments that the ratio represents a window into the mesospheric chemistry that links Na, NaO, O(3P), O2, and O3. It appears likely that the variability reflects the changing [O]/[O2] ratio within the sodium nightglow region, and thus represents a probe of this ratio. The second task involves laboratory studies of the loss rate coefficients of O2(b) molecules over the vibrational range of v = 3-8 range, using both O2 and O-atoms as colliders. This will lead to an improved understanding of the atmospheric production rates of these molecules and their production mechanisms. The third task is an investigation of the O2 Atmospheric band emissions seen in the mesosphere. It has been observed that the various vibrational levels do not vary in concert. The project will test the hypothesis that the emission intensity ratios can be related to variations in the mesospheric O-atom density. The fourth task seeks to explain a discrepancy between theory and observations for the oxygen red line emissions and those from the nitrogen doublet at 520 nm as they decay throughout the night. When the emissions are most intense in the early evening, there is a substantial difference between the observed and modeled intensity ratio, the red lines being more intense with respect to the nitrogen emissions than predicted. The project will carry out further measurements and data evaluations to understand the source of this difference. The broader impacts of these studies include the support of a postdoctoral scholar and contributions to other disciplines; for the latter, the O2 laboratory studies, which investigate the lower vibrational levels of the lower O2 electronic states, are of direct relevance to O2 COIL laser studies, to plasma etching, and to non-equilibrium processes in gas discharge system, while the sodium study will lead to important insights into the chemistry of meteor trails.