[P-PS05] Recent advances in the science of Venus

[PPS05-P07] Radiative Effects on the Formation of the Stably Stratified Layer in the Lower Atmosphere of Venus

*Yoshiyuki O. Takahashi¹, Yoshi-Yuki Hayashi¹, George HASHIMOTO², Kiyoshi Kuramoto³, Masaki Ishiwatari³, Hiroki Kashimura¹ (1.Graduate School of Science, Kobe University, 2.Department of Earth Sciences, Okayama University, 3.Department of Cosmosciences, Hokkaido University)

Keywords:Venus, one-dimensional radiative-convective equilibrium state, static stability

Past insitu observations of the atmosphere of Venus showed that the atmosphere is stable just below the cloud base down to about 30 km altitude, close to neutral around 20-30 km altitude, stable from about 20 km to about 10 km altitude, and probably almost neutral below there to the surface. However, our radiative-convective equilibrium calculation showed that the atmosphere is neutral from the surface to about 30 km altitude (Takahashi et al., 2024). In this study, the possible formation mechanism of the stable layer around 10-20 km altitude is investigated by the use of the radiative-convective equilibrium model. The radiative-convective equilibrium model composed of a radiative transfer model (Takahashi et al., 2023) and a dry convective adjustment. The radiative transfer calculation considers the absorption by H₂O, CO₂, CO, SO₂, HF, OCS, and N₂, the Rayleigh scattering, and the absorption and scattering by clouds. In the absorption by CO₂, the collision induced absorption is considered. In the convective adjustment, a dry adiabatic lapse rate is estimated by the use of the thermodynamic model of real gas of EOS-CG mixture model (Gernert and Span, 2016). We performed parameter experiments with changing profiles of composition mixing ratio within the observed range by the use of the radiative-convective equilibrium model. It was shown that a stable layer forms around 20-30 km altitude when we assume a composition profile with the mixing ratio close to the observed upper limit for H₂O and SO₂, and that close to the observed lower limit for CO. However, the achieved stability was lower than the observed one. In this study, it was shown that the use of the increased continuum absorption coefficient of CO₂ and/or H₂O, which are not well constrained observationally or experimentally, may be able to cause the formation of a stable layer with stability comparable to the observed one around 20-30 km altitude. This study has been published as Takahashi et al. (2024), https://doi.org/10.2151/jmsj.2024-025.