Non-local thermodynamic equilibrium studies of the 15-μm bands of CO₂ for atmospheric remote sensing

A new line-by-line non-local thermodynamic equilibrium (non-LTE) radiance model based on the GENLN2 radiative transfer code is presented. This is capable of high resolution spectral radiance calculations for the upper atmosphere. The authors describe the non-LTE model implementation and discuss the molecular state vibrational temperature input requirements for studies of the 15-μm n₂ bands of CO₂. Monochromatic and band-integrated radiance calculations have been performed for atmospheric limb view tangent heights between 50 and 120 km for non-LTE nighttime and daytime conditions. Two model atmospheres are considered, the US 1976 Standard and a subarctic summer, which show, respectively, mean and large radiance differences from a reference LTE radiance calculation. Non-LTE radiance considerations are shown to be important for the 15-μm CO₂ bands for tangent heights greater than 70 km, the magnitude of the divergence from LTE values and diurnal variation being dependent on the band and kinetic temperature profile. -from Authors