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J.B. Dalton (U.S. Geological Survey), J.B. Pollack (NASA-Ames), D.H. Grinspoon (SwRI), B. Bezard, C. de Bergh (Observatoire de Paris)
Near-infrared spectral observations of Venus in the atmospheric transmission windows located at 1.2,1.7 and 2.3 microns have provided a wealth of information regarding the abundances of atmospheric constituents. Probing the atmosphere below the cloud decks is important for models of atmospheric composition and evolution, circulation and transport, and surface-atmosphere interactions. High-temperature databases of gas absorption coefficients are necessary for realistic simulation of the spectral properties of hot carbon dioxide and water in the atmosphere of Venus.
We have modeled telescopic spectra in the 1.7 micron range obtained by Bezard and de Bergh of Venus' nightside thermal emission using a radiative transfer program which includes emission, absorption, and scattering by atmospheric gases and particles. This wavelength range is particularly sensitive to the water and chlorine abundances between 5 and 35 km altitude. Previous estimates of the water and chlorine abundances (Young, 1973; Pollack et al., 1993) did not constrain vertical gradients for HCl in the atmosphere. The present model suggests that an abundance of HCl of .4 ppm above the clouds, consistent with previous estimates, is applicable but that the abundance varies within and below the cloud decks. Simulations indicate that the chlorine abundance may in fact decrease with altitude within the cloud decks, and apparently increases to approximately 1 ppm within 5 km of the surface.
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