CEDAR: Studies of the O2(a-X) Infrared Atmospheric Band Nightglow Emission

Earth’s upper atmosphere continuously produces a weak radiation known as airglow. Solar radiation absorbed by the constituents of the middle and upper atmosphere is the energy source that enables airglow. Light emission observed during the day is called dayglow. Several chemical reactions, energy transfer processes, and other excitation mechanisms persist throughout the night and contribute to the observed emission called nightglow. The O2 Infrared Atmospheric band (IR A-band) is the strongest molecular oxygen nightglow emission in Earth’s mesosphere, at an altitude of approximately 90 km. This emission has been the target of space-based observations for several decades. Despite numerous studies, the details of the underlying excitation processes are not well understood, and there is no consensus on the interpretation of the observed altitude profiles. Consequently, extensive data sets from existing observations cannot be fully exploited, e.g., to determine atomic oxygen concentration or to accurately model waves propagating in the upper atmosphere. Advancing our understanding of this important nightglow emission is the key scientific objective of this project. The proposal team will analyze and model extant data sets of the IR A-band nightglow emission from space-based observations by satellites and sounding rockets, with special emphasis on the possible coupling between the OH layer and electronically excited O2(a), the species responsible for the IR A-band emission. This coupling is likely induced by molecular energy transfer between vibrationally excited OH with ground-state O2. This research is inspired by the discovery of multi-quantum vibrational-to-electronic energy transfer in collisions between vibrationally excited OH and O atoms. These pathways generate excited O(1D) and were shown to enhance other nightglow emissions (e.g., the CO2 4.3-micrometer emission). The science objective of this research is to quantify the sources of O2(a) and provide a state-of-the art interpretation of the O2 IR A-band emission. The results of this work will benefit scientists who model planetary atmospheres within and beyond our solar system, as well as theoreticians and experimentalists, and will enhance the scientific returns of ground- and space-based remote sensing observations. Just as important, this research project will contribute to the training and formative research experiences of one or more postdoctoral fellows and summer undergraduate students. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.