Evidence of non‐LTE effects in mesospheric water vapor from spectrally‐resolved emissions observed by CIRRIS‐1A

Evidence of non‐LTE effects in mesospheric water vapor as determined by infrared spectral emission measurements taken from the space shuttle is reported. A cryogenic Michelson interferometer in the CIRRIS‐1A shuttle payload yielded high quality atmospheric infrared spectra. These measurements demonstrate the enhanced daytime emissions of H 2 O (020→010) which are the result of non‐LTE processes and in agreement with non‐LTE models. The radiance ratios of H 2 O (010→000) and (020→010) Q(1) transitions during daytime are compared with non‐LTE model calculations to assess the vibration‐to‐vibration exchange rate between H 2 O and O 2 in the mesosphere. An exchange rate of 1.2×10 −12 cm³ s −1 is derived.