The main goal of this study is to uniquely identify the nighttime physical mechanisms of excitation and quenching of CO2 molecular vibrations in the mesosphere and lower thermosphere MLT. The…

This is a $262,885.50 grant awarded by the National Aeronautics and Space Administration (NASA) to the Catholic University of America (CUA) to study the nighttime physical mechanisms of excitation and quenching of carbon dioxide (CO2) molecular vibrations in the mesosphere and lower thermosphere. The goal is to utilize nighttime limb observations of the CO2 4.3 and 15 micron emissions and hydroxyl (OH) 1.6 and 2 micron emissions collected by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the TIMED satellite to better understand the coupling of the CO2 emissions and retrieve CO2 volume mixing ratios and temperatures. The study aims to address the lack of understanding around the nighttime 4.3 micron emission generation mechanisms. This grant does not have a set-aside designation, and CUA is performing the work as the prime contractor without major subcontractors. The award is part of NASA's broader research programs studying the Earth's atmosphere and space environment.

The main goal of this study is to uniquely identify the nighttime physical mechanisms of excitation and quenching of CO2 molecular vibrations in the mesosphere and lower thermosphere MLT. The production of vibrationaly excited OH molecules and subsequent vibrational energy transfer OH N2 provides significant non thermal excitation of the CO2 vibrations responsible for the 4.3 m emissions. We will utilize as diagnostics, the nighttime limb observations of the CO2 4.3 and 15 m emissions and OH 1.6 and 2 m emissions of MLT collected by the saber instrument on board the timed satellite. A previous study demonstrated significant coupling of the CO2 4.3 and 15 m emissions in MLT, and applied self consistent analysis of simultaneous saber day time limb observations of both emissions to retrieve CO2 VMR and temperature in MLT for more than 13 years observations. Similar simultaneous night time observations remained, however, unprocessed: due to the lack of understanding of the night time 4.3 m emissions generation mechanisms night time temperatures are still operationally retrieved from the saber 15 m channel radiances using CO2 densities obtained from the waccm model. The study is compelling despite CO2 being a chemically stable molecule above 80 KM, where diurnal tide has large amplitude, CO2 has significant gradients. As a result, upwelling down welling patterns associated with the diurnal tide will produce a tidal signature in CO2 leading to significant day night CO2 differences and corresponding variations of both 4.3 and 15 m emissions.