NON-LOCAL-THERMODYNAMIC-EQUILIBRIUM POPULATIONS OF THE 1ST VIBRATIONAL EXCITED-STATE OF CO IN THE MIDDLE ATMOSPHERE

A non-LTE radiative transfer model for the population of the CO(1) vib rational state in the middle atmosphere is presented. Radiative transf er is treated by using the Curtis matrix method. The transmittances ne eded for the Curtis matrix have been computed by using the GENLN2 line -by-line radiance/transmittance code. A study of the radiative and col lisional processes and atmospheric parameters that affect the populati on of CO(1) populations has been performed. We find that the troposphe ric kinetic temperature and CO abundance profiles play an important ro le through radiative coupling in the population of mesospheric CO(1) a t night-time. During the day, the solar flux and the mesospheric CO ab undance are the main factors determining the CO vibrational temperatur e in the mesosphere. Non-thermal collisions with the atmospheric N2 (1 ) are also shown to be important for the daytime population of CO(1) i n that region. The consequences of these results for the retrieval of CO abundances from the remote sensing of radiance at 4.7 mum are discu ssed.