Non-local thermodynamic equilibrium limb radiance from O₃ and CO₂ in the 9-11 μm spectral region

Satellite remote sensing of mesospheric and thermospheric O₃ abundance in the terrestrial atmosphere often uses 9-11 μm thermal emission. In this paper, we apply a line-by-line non-local thermodynamic equilibrium (non-LTE) radiance model to this spectral region and investigate the conditions of LTE breakdown and the effect that this has on the limb radiance measured by an i.r. sounder. Monochromatic and band-integrated radiance calculations have been performed for limb view tangent heights between 55 and 105 km under daytime and nightime conditions. Non-LTE emission from both O₃ and CO₂ are shown to be important with the divergence of radiance from LTE values and the diurnal variation being band dependent. We have shown that the contribution of the CO₂ bands to the Limb Infrared Monitor of the Stratosphere O₃ channel is significant for daytime conditions at tangent heights above about 60 km. A study has been made to choose O₃ sounding channel spectral passbands for the High Resolution Dynamics Limb Sounder. High resolution calculations are required to determine those spectral intervals that will filter radiance from selected bands and characterize their non-LTE behavior. This will allow for improved O₃ retrievals above 70 km and non-LTE studies.