Analysis of the SABER 4.3-μ m Nighttime Radiance and Implications for the Temperature and CO2 vmr Retrieval

The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument measures the CO₂ 4.3-μ m nighttime emission with a signal-to-noise ratio which equals to 1 at 130 km. These measurements can be used to derive the carbon dioxide abundance above 75 km during nighttime. CO₂ abundance is needed not only to understand the energy balance of the MLT region but also to accurately derive the kinetic temperature in that region from the measurements taken at 15-μ m. However, the nighttime non-LTE mechanisms affecting the 4.3-μ m CO₂ vibrational state population are not well known and therefore CO₂ abundance cannot still be accurately retrieved from SABER measurements at night. The analysis of SABER nighttime measurements at 4.3-μ m presented here shows that the radiance is reproduced only if an efficient energy transfer from OH to CO₂ via N₂ , whereby 2.8-3 N₂(1) molecules are excited after quenching of one OH(υ), is considered. We also present the implications of including such a process in the simultaneous T_k/CO₂ retrieval results.