Global distribution of CO<inf>2</inf> in the upper mesosphere as derived from UARS/ISAMS measurements

The latitudinal and seasonal variations of the CO<inf>2</inf> concentration between 70 and 100 km are investigated using the 4.6 μm daytime measurements made by the Improved Stratospheric and Mesospheric Sounder (ISAMS) on the Upper Atmospheric Research Satellite (UARS). The analysis uses a detailed nonlocal thermodynamic equilibrium model of the CO<inf>2</inf> states emitting in the 4.3 μm spectral region and the GENLN2 line-by-line radiance code to update an earlier study by López-Puertas et al., [1998b]. The differences in the CO<inf>2</inf> volume mixing ratio between the equator and the illuminated pole in the upper mesosphere are shown to be smaller than the detection limit established by the uncertainties in the data (approximately 10% at 85 km, 14% at 90 km, 23% at 95 km, and 28% at 100 km). Copyright 2000 by the American Geophysical Union.