NONLOCAL THERMODYNAMIC-EQUILIBRIUM LIMB RADIANCE FROM O-3 AND CO2 IN THE 9-11-MU-M SPECTRAL REGION

Satellite remote sensing of mesospheric and thermospheric O-3 abundanc e in the terrestrial atmosphere often uses 9-11 mu m thermal emission. In this paper, we apply a line-by-line non-local thermodynamic equili brium (non-LTE) radiance model to this spectral region and investigate the conditions of LTE breakdown and the effect that this has on the l imb radiance measured by an i.r. sounder. Monochromatic and band-integ rated radiance calculations have been performed for limb view tangent heights between 55 and 105 km under daytime and nighttime conditions. Non-LTE emission from both O-3 and CO2 are shown to be important with the divergence of radiance from LTE values and the diurnal variation b eing band dependent. We have shown that the contribution of the CO2 ba nds to the Limb Infrared Monitor of the Stratosphere O-3 channel is si gnificant for daytime conditions at tangent heights above about 60 km. A study has been made to choose O-3 sounding channel spectral passban ds for the High Resolution Dynamics Limb Sounder. High resolution calc ulations are required to determine those spectral intervals that will filter radiance from selected bands and characterize their non-LTE beh avior. This will allow for improved O-3 retrievals above 70 km and non -LTE studies.