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

[PPS05-03] Attempts to improve a Venus' atmospheric chemical model with a focus on temperature

*桑山 慎也¹、はしもと じょーじ¹、樫村 博基²、松嶋 俊樹²、杉本 憲彦³、高木 征弘⁴、林 祥介² (1.岡山大学地球科学、2.神戸大学惑星、3.慶応大学日吉物理、4.京都産業大学理学)

キーワード：金星、大気の運動、物質循環

In this study, we implemented chemical and cloud processes into the Venus atmospheric general circulation model (GCM), AFES-Venus, and aimed to obtain chemical species distributions consistent with observations. AFES-Venus has achieved certain successes, such as reproducing the strong eastward winds (super-rotation) observed at an altitude of 65 km in Venus' atmosphere. On the other hand, implemented chemical and cloud processes have been tested using a simplified meridional chemical model, and it has been confirmed that the meridional distribution of chemical species calculated with appropriate parameters does not contradict observations. However, chemical species distributions calculated using the standard settings of AFES-Venus significantly differ from observations. Specifically, at altitudes above 40 km, the CO mixing ratio is more than twice the observed value, the H₂O vapor mixing ratio is less than one-tenth of the observed value, and the H₂SO₄ vapor mixing ratio at the cloud base in low latitudes is about one-third of the observed value. Additionally, near-infrared observations suggest that clouds are optically thickest in low latitudes, whereas the calculated column density of cloud mass loading is about five times larger in high latitudes than in low latitudes, contradicting observations. To address this issue, we attempted to modify the calculation settings of AFES-Venus and bring the chemical species distribution closer to observations. The distribution of CO and H₂O vapor was thought to be inconsistent with observations due to inefficient vertical transport. Therefore, by increasing the vertical diffusion coefficient to improve the efficiency of vertical transport, the CO mixing ratio in the upper layer decreased, and the H₂O vapor mixing ratio in the upper layer increased, resolving the inconsistency with the observations. On the other hand, it is not clear why the H₂SO₄ and cloud mass loading distribution is inconsistent with observations. In this study, we focused on the temperature, which influences the condensation and evaporation processes, to explore the cause of the inconsistency in H₂SO₄ and cloud mass loading distributions. The temperature calculated by the standard settings of AFES-Venus differs by up to about 50 K from the Venus Standard Atmosphere (VIRA). It was considered that this temperature discrepancy could be the cause of the inconsistency in these distributions. Therefore, in this study, we corrected the temperature discrepancy caused by the assumption of a constant specific heat capacity (Cp) in AFES-Venus, and then modified the relaxation field for Newtonian cooling to reduce the temperature bias compared to VIRA. The H₂SO₄ vapor and cloud mass loading calculated with the changed setting increased to some extent in the low latitudes compared with before the setting change. This increase in H₂SO₄ vapor and cloud mass loading at low latitudes is likely due to the change in circulation caused by modifying the Newtonian cooling relaxation field.