Impact of the Turbulent Vertical Mixing on Chemical and Cloud Species in the Venus Cloud Layer

The Venusian atmosphere hosts a 10 km deep convective layer that has been studied by various spacecrafts. However, the impact of the strong vertical mixing on the chemistry of this region is still unknown. This study presents the first realistic coupling between resolved small-scale turbulence and a chemical network. The resulting vertical mixing is different for each species: those with longer chemical timescales will tend to be well-mixed. Vertical eddy diffusion due to resolved convection motions was estimated, ranging from 102 to 104 m2/s for the 48-55 km convective layer, several orders of magnitude above the typically used value. In the 48-55 km convective layer, the impact of the small-scale turbulence on the cloud layer boundaries was between 200 m and 1 km. The impact of turbulence on cloud chemistry is consistent with Venus Express/Visible and Infrared Thermal Imaging Spectrometer observations. The observability at the cloud-top of small-scale turbulence by VenSpec-U spectrometer would be challenging. Venus hosts a global sulfuric acid cloud layer between 45 and 70 km. A convective layer is present between roughly 50 and 60 km, with its variability in latitude and local time assessed by observation, with a thicker layer at high latitude and at night. One question that remains unclear is how this turbulence mixes momentum, heat, and chemical species. Especially, the impact of the strong vertical mixing on the chemistry of this region is still unknown. To investigate this topic, we use a convection-resolving model coupled for the first time with a realistic chemical network. The resulting vertical mixing is different for each species: those with longer chemical timescales will tend to be well-mixed. 1D and global circulation models use the so-called vertical eddy diffusion approach to represent turbulent motion, quantified in our model and underestimated in chemistry models. The small-scale turbulence in the cloud layer causes a variation in the altitude of the top and bottom boundaries of the cloud. Our model shows that the impact of turbulence on cloud chemistry corresponds well to what has been observed by satellites. In the future, the EnVision mission will be able to observe chemical species at the small turbulence scales. Estimation for the first time of the spatial and temporal variability of chemical species due to vertical mixing Quantification of the vertical eddy diffusion coefficient, order of magnitude above typical used values Cloud-top altitudes change by 0.2-1 km due to vertical convective mixing and gravity waves