Middle and upper atmosphere pressure‐temperature profiles and the abundances of CO2 and CO in the upper atmosphere from ATMOS/Spacelab 3 observations

Abstract

Based on a new approach, profiles of kinetic temperature and atmospheric pressure between 20 and 116 km altitude and CO2 and CO volume mixing ratios between 70 and 116 km have been derived from the ∼0.01‐cm−1 resolution infrared solar occultation spectra recorded by the atmospheric trace molecular spectroscopy (ATMOS) Fourier transform spectrometer during the Spacelab 3 shuttle mission (April 29 to May 6, 1985). The physical model and CO2 profile results have been obtained from simultaneous multiscan least squares fitting of microwindows containing CO2 lines with temperature‐dependent and temperature‐independent intensities and N2 lines with temperature‐independent intensities. The analysis included the retrieval of tangent height separations between spectra in the lower stratosphere, where independent information shows drifts of the sun tracker field of view on the solar disk. The physical model results are compared with climatological profiles, lower thermospheric temperatures computed with the MSISE‐90 model, and other data. The CO2 retrievals indicate a nearly constant volume mixing ratio of 320 ± 35 ppmv (parts per million, 10−6, by volume) in the 70‐to 90‐km altitude region with a rapid decline in the CO2 volume mixing ratio beginning between 90 and 100 km; at 116 km the CO2 volume mixing ratio has declined to about 70 ppmv and is equal to the CO volume mixing ratio, which has been derived from fits to the (1‐0) CO vibration‐rotation band. The absorption by the v2 + v3 ‐ v2 band of CO2 has been analyzed to quantify nonlocal thermodynamic equilibrium (non‐LTE) effects in the upper mesosphere and lower thermosphere. Up to an altitude of 100 km, the results indicate that the vibrational temperature of the v2 state of CO2 is within 5 K of the kinetic temperature. At higher altitudes, non‐LTE effects are observable with the vibrational temperature of the v2 state cooler than the kinetic temperature by 40 K (48°S) and 70 K (30°N) at 112 km. Above 112 km, lines of the v2 + v3 ‐ v2 band are too weak to be observed in the ATMOS spectra.