Radiative Effects on the Formation of the Stably Stratified Layer in the Lower Atmosphere of Venus

The formation of the stable layer below about 2 x 106 6 Pa pressure level (about 20 km altitude) of the atmosphere of Venus detected by in situ observations is investigated by the use of a radiative-convective equilibrium model. We demonstrate that, assuming mixing ratio profiles of absorbers to be at the upper limits of the observed ranges for H2O 2 O and SO2 2 and the lower limit for CO, a stable layer forms as a radiative-convective equilibrium state, but its stability is lower than the observed one. Also, increasing the continuum absorption coefficient of CO2 2 and/or H2O, 2 O, which are not well constrained observationally or experimentally, results in the formation of a stable layer whose stability is comparable to the observed one. These results suggest a practical method to form the stable layer in the dynamical models of the Venus atmosphere. Further, these results indicate that the important targets of future observations and laboratory measurements are to obtain more precise profiles of the mixing ratios of H2O, 2 O, CO, and SO2 2 in the Venus atmosphere, and to determine the continuum absorption coefficients of those.