The main objective of this project is to analyze and model observations of the 630-nm atomic oxygen red line emission from ionospheric modification (IM) experiments and to extract the corresponding local O-atom densities. In contrast to the common practice of ignoring oxygen atoms in interpreting such observations in the past, recent experimental studies on the relaxation of O(1D) by O(3P) have revealed the dominant role oxygen atoms play in controlling the lifetime of O(1D) at altitudes relevant to IM experiments. Using the most up-to-date rate coefficients for collisional relaxation of O(1D) by O, N2, and O2, it is now possible to analyze reliably the red line decays observed in IM experiments and thus probe the local O-atom density in the ionosphere. This project will take advantage of an innovative approach to remotely probe O-atoms at the altitudes relevant to IM experiments, to test the current models for O-atom density in the ionosphere, and to study its temporal, seasonal, altitude and spatial variation in the vicinity of heating facilities. Relevant data sets will be acquired from IM sites, with emphasis on data from HAARP and EISCAT, in order to determine the O-atom densities implied from the decays and to make comparisons with standard atmospheric composition models such as MSIS and Jacchia. The results will likely be of use in planning new IM experiments, and the ultimate goal is to generate ionospheric O-atom maps over a particular site, to be compared to models. Remote sensing of O-atom densities and monitoring of their fluctuations in the ionosphere has been a particularly challenging problem. The broader impacts of the project include international collaborative efforts between Tromso University, Norway, Lancaster University, U.K., the Air Force Research Laboratory, and SRI International, and the contribution to the training and research experiences of summer undergraduate students at SRI.
