The Effect of Collisional Line Broadening on the Spectrum and Fluxes of Thermal Radiation in the Lower Atmosphere of Venus

Abstract

The absorption spectrum and thermal radiation fluxes are calculated for the lower atmosphere of Venus in the far-wing approximation based on the theory of the collisional broadening of spectral lines. The results are in good agreement with the available experimental data. An outgoing thermal radiation flux is about 2.6 W/m 2 near the planetary surface. This indicates that free convection significantly contributes to the thermal balance of the lower troposphere. The fluxes obtained in this study were compared to those calculated on the basis of empirical models of the spectral line profile. It was shown that the far wings of the CO 2 lines considerably affect the radiative transfer in the transparency windows. This effect becomes weaker when the contribution of the absorption of minor constituents, primarily water vapor, increases. The profiles of absorption lines of minor constituents do not influence the thermal radiation fluxes.

Venus surface data extraction from VIRTIS/Venus Express measurements: Estimation of a quantitative approach

“…The extreme temperature and pressure regime in the deep atmosphere of Venus, however, makes high demands on new theoretical and methodical work including hot gaseous absorption bands, far spectral line wings and pressure‐induced absorption. Much effort has been devoted to explaining the effects of spectral line shape under high temperature and pressure conditions [e.g., Burch et al , 1969; Tonkov et al , 1996; Filippov and Tonkov , 1998; Ma et al , 1999; Tvorogov and Rodimova , 1995; Afanasenko and Rodin , 2005], but up to now, the related works do not offer a self‐sufficient model that is suitable for practical calculations over the full spectral range that is of interest for surface and deep atmosphere studies. This is the reason why currently most simulation algorithms make use of empirically determined continuum opacities to fit the observations.…”

CO2 absorption in band wings in near IR

“…Authors of [6] suggested using empirical relations for the absorption in wings of the three CO 2 bands, since calculations with the use of interference disagree with experiments. It is shown in [19] (see also [20]) that the calculation [21] with the use of line interference near the 1.18 μm band wing underestimates the CO 2 absorption; an empirical profile is suggested which describes the absorption in this region.…”

“…Comparison with the Bezard profile[20] for the 8300 cm -1 band. Combined profile found in this work is shown by the heavy curve, its parts that answer different monomials, by thin curves, empirical profile[20], by the dashed curve; Δω = 0-250 cm -Δω Deviations from a Lorentzian profile for the 1.2 , 1.2195 , 1.4 , 2.7 , 4.3 μm CO 2 bands calculated in (a) work[8] and (b) this work.…”