Sulfur‐water chemistry plays an important role in the middle atmosphere of Venus. Ground‐based observations have found that simultaneously observed SO2and H2O at ~64 km vary with time and are temporally anticorrelated. To understand these observations, we explore the sulfur‐water chemical system using a one‐dimensional chemistry‐diffusion model. We find that SO2and H2O mixing ratios above the clouds are highly dependent on mixing ratios of the two species at the middle cloud top (58 km). The behavior of sulfur‐water chemical system can be classified into three regimes, but there is no abrupt transition among these regimes. In particular, there is no bifurcation behavior as previously claimed. We also find that the SO2self‐shielding effect causes H2O above the clouds to respond to the middle cloud top in a nonmonotonic fashion. Through comparison with observations, we find that mixing ratio variations at the middle cloud top can explain the observed variability of SO2and H2O. The sulfur‐water chemistry in the middle atmosphere is responsible for the H2O‐SO2anticorrelation at 64 km. Eddy transport change alone cannot explain the variations of both species. These results imply that variations of species abundance in the middle atmosphere are significantly influenced by the lower atmospheric processes. Continued ground‐based measurements of the coevolution of SO2and H2O above the clouds and new spacecraft missions will be crucial for uncovering the complicated processes underlying the interaction among the lower atmosphere, the clouds, and the middle atmosphere of Venus.
The current Venus climate is largely regulated by globally covered concentrated sulfuric acid clouds from binary condensation of sulfuric acid (H2SO4) and water (H2O). To understand this complicated H2SO4‐H2O gas‐cloud system, previous theoretical studies either adopted complicated microphysical calculations or assumed that both H2SO4and H2O vapor follow their saturation vapor pressure. In this study, we developed a simple one‐dimensional cloud condensation model including condensation, diffusion and sedimentation of H2SO4and H2O but without detailed microphysics. Our model is able to explain the observed vertical structure of cloud and upper haze mass loading, cloud acidity, H2SO4, and H2O vapor, and the mode‐2 particle size on Venus. We found that most H2SO4is stored in the condensed phase above 48 km, while the partitioning of H2O between the vapor and clouds is complicated. The cloud cycle is mostly driven by evaporation and condensation of H2SO4rather than H2O and is about seven times stronger than the H2SO4photochemical cycle. Most of the condensed H2O in the upper clouds is evaporated before the falling particles reach the middle clouds. The cloud acidity is affected by the temperature and the condensation‐evaporation cycles of both H2SO4and H2O. Because of the large chemical production of H2SO4vapor and relatively inefficient cloud condensation, the simulated H2SO4vapor above 60 km is largely supersaturated by more than two orders of magnitude, which could be tested by future observations.
more » « less- NSF-PAR ID:
- 10446069
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Planets
- Volume:
- 127
- Issue:
- 3
- ISSN:
- 2169-9097
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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