(X 3 − g , v). In contrast to the previous models of kinetics of O 2 (a 1 g ) and O 2 (b 1 + g ), our model takes into consideration the following basic facts: first, photolysis of O 3 and O 2 and the processes of energy exchange between the metastable products of photolysis involve generation of oxygen molecules on highly excited vibrational levels in all considered electronic states -b 1 + g , a 1 g and X 3 − g ; second, the absorption of solar radiation not only leads to populating the electronic states on vibrational levels with vibrational quantum number v equal to 0 -O 2 (b 1 + g , v=0) (at 762 nm) and O 2 (a 1 g , v=0) (at 1.27 µm), but also leads to populating the excited electronicvibrational states O 2 (b 1 + g , v=1) and O 2 (b 1 + g , v=2) (at 689 nm and 629 nm). The proposed model allows one to calculate not only the vertical profiles of the O 2 (a 1 g , v=0) and O 2 (b 1 + g , v=0) concentrations, but also the profiles of2)] and O 2 (X 3 − g , v=1-35). In the altitude range 60-125 km, consideration of the electronic-vibrational kinetics significantly changes the calculated concentrations of the metastable oxygen molecules and reduces the discrepancy between the altitude profiles of ozone concentrations retrieved from the 762-nm and 1.27-µm emissions measured simultaneously.

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Abstract. This paper describes a methodology for water vapor retrieval in the mesosphere-lower thermosphere (MLT) using 6.6 µm daytime broadband emissions measured by SABER, the limb scanning infrared radiometer on board the TIMED satellite. Particular attention is given to accounting for the non-local thermodynamic equilibrium (non-LTE) nature of the H 2 O 6.6 µm emission in the MLT. The non-LTE H 2 O(ν 2 ) vibrational level populations responsible for this emission depend on energy exchange processes within the H 2 O vibrational system as well as on interactions with vibrationally excited states of the O 2 , N 2 , and CO 2 molecules. The rate coefficients of these processes are known with large uncertainties that undermines the reliability of the H 2 O retrieval procedure. We developed a methodology of finding the optimal set of rate coefficients using the nearly coincidental solar occultation H 2 O density measurements by the ACE-FTS satellite and relying on the better signal-to-noise ratio of SABER daytime 6.6 µm measurements. From this comparison we derived an update to the rate coefficients of the three most important processes that affect the H 2 O(ν 2 ) populations in the MLT: a) the vibrational-vibrational (V-V) exchange between the H 2 O and O 2 molecules; b) the vibrationaltranslational (V-T) process of the O 2 (1) level quenching by collisions with atomic oxygen, and c) the V-T process of the H 2 O(010) level quenching by collisions with N 2 , O 2 , and O. Using the advantages of the daytime retrievals in the MLT, which are more stable and less susceptible to uncertainties Correspondence to: A. G. Feofilov (artem-feofilov@cua-nasa-gsfc.info) of the radiance coming from below, we demonstrate that applying the updated H 2 O non-LTE model to the SABER daytime radiances makes the retrieved H 2 O vertical profiles in 50-85 km region consistent with climatological data and model predictions. The H 2 O retrieval uncertainties in this approach are about 10% at and below 70 km, 20% at 80 km, and 30% at 85 km altitude.