[P-PS04] Recent advances in the science of Venus

[PPS04-12] Chemical species and cloud water distributions in the Venus atmosphere calculated by a GCM with chemical and cloud microphysical processes

★Invited Papers

*KUWAYAMA Shinya¹, George HASHIMOTO¹, Hiroki Kashimura², Toshiki Matsushima², Norihiko Sugimoto³, Masahiro Takagi⁴, Yoshi-Yuki Hayashi² (1.Department of Earth Sciences, Okayama University, 2.Department of Planetology, Kobe University, 3.Department of Physics, Keio University, 4.Faculty of Science, Kyoto Sangyo University)

Keywords:Venus, material circulation, GCM

AFES-Venus (Sugimoto et al., 2014), one of the Venus atmospheric general circulation models, simulates strong zonal winds of about 100 m/s, called super-rotation (SR), observed at the cloud-top altitude of Venus. On the other hand, we have developed a meridional chemical model for the Venus atmosphere (Kuwayama and Hashimoto in preparation), which include processes of chemistry, transportation and cloud microphysic can calculate the meridional distribution of minor constituents such as CO and H₂O. By giving a meridional circulation flow field and setting some parameters to values considered reasonable for Venus, our chemical model produces a meridional distribution of atmospheric minor constituents that is consistent with observed. Then, we have implemented the chemical and cloud microphysics scheme in AFES-Venus and calculated the distribution of atmospheric minor constituents. In contrast to the result of the meridional model, the CO concentration was several times higher than that observed at altitudes >30 km, and the H₂O concentration was a fraction of that observed at altitudes >40 km. The concentration of CO is higher in the upper layers because it is produced at altitudes of about 90 km and decomposed at altitudes of <20 km (Krasnopolsky, 2012). The higher CO concentration in the upper layer is due to the accumulation of CO there due to insufficient vertical transport. The concentration of H₂O is lower in the upper layers because it is produced at altitudes of 30-40 km and decomposed at altitudes of about 62 km (Krasnopolsky, 2012). The lower H₂O concentration in the upper layer is also due to insufficient vertical transportation. Using a higher vertical diffusion coefficient would decrease CO and increase H₂O in the upper layer, however, that would weaken SR (Sugimoto et al., 2019). We have found that it is difficult to obtain results that both CO/H₂O concentration and SR are consistent with the observation by setting the same value of vertical diffusion coefficient at all altitude. Then, we have succeeded in obtaining such observationally consistent results by using vertical diffusion whose coefficient varies with altitudes. When the vertical diffusion coefficient of the upper layer is increased by three to four orders of magnitude larger than the lower layer and that of the lower layer is kept to AFES-Venus standard setting, the calculated distribution of CO and H₂O is almost consistent with observed and SR is maintained. However, the latitudinal distributions of H₂SO₄ vapor and cloud water loading differ from observations.