Evidence for Non-Local Thermodynamic Equilibrium in the v 3 Mode of Mesospheric CO2 from Stratospheric and Mesospheric Sounder Measurements

The measurements of the 4.3 µm CO2 emission from the terrestrial atmosphere carried out by the Stratospheric and Mesospheric Sounder (SAMS) on Nimbus 7 are presented. The data cover radiances from 50oS to 70oN, altitudes from 30 km to 140 km, and have been taken during a period of nearly four years from 1978 to 1982. The most important features in the data are described and qualitatively discussed. The theoretical treatment necessary to analyze the data is developed. By using a non-LTE radiative transfer model, the mechanisms responsible for the most outstanding feature in the data, the large day to night difference in the radiances, have been established.