One-dimensional Microphysics Model of Venusian Clouds from 40 to 100 km: Impact of the Middle-atmosphere Eddy Transport and SOIR Temperature Profile on the Cloud Structure

Abstract

We conducted a simulation of H _2 SO _4 vapor, H _2 O vapor, and H _2 SO _4 –H _2 O liquid aerosols from 40 to 100 km, using a 1D Venus cloud microphysics model based on the one detailed in Imamura & Hashimoto. The cloud distribution obtained is in good agreement with in situ observations by Pioneer Venus and remote-sensing observations from Venus Express (VEx). Case studies were conducted to investigate sensitivities to atmospheric parameters, including eddy diffusion and temperature profiles. We find that efficient eddy transport is important for determining upper haze population and its microphysical properties. Using the recently updated eddy diffusion coefficient profile by Mahieux et al., our model replicates the observed upper haze distribution. The H _2 O vapor distribution is highly sensitive to the eddy diffusion coefficient in the 60–70 km region. This indicates that updating the eddy diffusion coefficient is crucial for understanding the H _2 O vapor transport through the cloud layer. The H _2 SO _4 vapor abundance varies by several orders of magnitude above 85 km, depending on the temperature profile. However, its maximum value aligns well with observational upper limits found by Sandor et al., pointing to potential sources other than H _2 SO _4 aerosols in the upper haze layer that contribute to the SO _2 inversion layer. The best-fit eddy diffusion profile is determined to be ∼2 m ^2 s ^−1 between 60 and 70 km and ∼360 m ^2 s ^−1 above 85 km. Furthermore, the observed increase of H _2 O vapor concentration above 85 km is reproduced by using the temperature profile from the VEx/SOIR instrument.

Keywords

• Venus
• Atmospheric clouds
• Atmospheric composition
• Planetary atmospheres
• Atmospheric evolution