CO2 in the MLT: Constraining the CO2(υ2)-O Quenching Rate Coefficient.

Abstract:

Carbon dioxide plays an important role in the terrestrial atmosphere, with infrared emission in the 15 μm CO₂ band (I_15μm) providing the dominant cooling mechanism in the mesosphere/lower thermosphere (MLT) region via interaction with atomic O. This CO2(υ₂)-O quenching rate coefficient is poorly understood and current estimates vary by a factor 3-4, with a significant discrepancy between laboratory measurements and those provided by satellite remote sensing. However, the true value of this rate coefficient is of vital importance in understanding both the energetics of the MLT region and for temperatures retrievals from measurements of I_15μm.

This work builds upon and extends an existing methodology developed by Feofilov et al. (2012) who used TIMED/SABER satellite instrument data to retrieve the CO₂(υ₂)-O quenching rate coefficient using a synergy of atmospheric and ground-based lidar temperature measurements. Using the SABER overflights of the Fort Collins (CO) lidar, these authors derived the altitude variation of the CO₂(υ₂)-O quenching rate. The latter demonstrated deficiency of the current non-LTE model of the 15 μm CO₂ emission which obviously misses some so far unknown mechanisms of non-thermal excitation of the CO₂(υ₂) vibrations. Current work involves several other lidar locations and is aimed at assessing whether there is a spatio-temporal variability component to this rate coefficient, and what this could reveal about these additional energy sources and sinks in the real atmosphere that are currently not accounted for in the non-LTE model.