Non-local-thermodynamic-equilibrium populations of the first vibrational excited state of CO in the middle atmosphere

Radiative transfer is treated by using the Curtis matrix method. We find that the tropospheric kinetic temperature and CO abundance profiles play an important role through radiative coupling in the population of mesospheric CO(1) at night-time. During the day, the solar flux and the mesospheric CO abundance are the main factors determining the CO vibrational temperature in the mesosphere. Non-thermal collisions with the atmospheric N₂(1) are also shown to be important for the daytime population of CO(1) in that region. The consequences of these results for the retrieval of CO abundances from the remote sensing of radiance at 4.7 μm are discussed. -from Authors