IntroductionUnlike the other terrestrial bodies in the Solar System, Venus is shrouded in a thick, multi-layered cloud at an altitude ranging from 48 to 70 kilometers[1]. These clouds consist of droplets of liquid SO₂ (70–95% by mass) and H₂O, divided into three modes with radii of approximately 0.3, 1, and 2 micrometers, respectively[2].The lack of in situ observations (only one in-situ profil of the cloud droplets characteristics[2]) means we have to actively try to model these clouds to understand them. The models developed so far are primarily 1D[3-7], and the few 2D and 3D models are restricted to simplified equilibrium schemes[8-11]. Here, we present the first 3D simulation of Venus's clouds using the Venus PCM[12-13], a global climate that includes chemistry, radiative transfer and dynamics, coupled with the microphysical scheme MAD-VenLA[14-16]. We use this opportunity to make comparison with Akatsuki UV observations. MethodWe coupled the MAD-VenLA model, developed by Guilbon[14], Määttänen[15] and Streel[16], with the Venus PCM. MAD-VenLA is a modal model that describes two particle modes with a lognormal shape and fixed standard deviation. It includes a homogeneous nucleation scheme[17], a simplified parametrization of heterogeneous nucleation, and Brownian coagulation, condensation, and evaporation[14-15]. Additionally, MAD-VenLA incorporates mode merging[18], which allows particles to be transferred from one mode to another. In its latest version, a sedimentation scheme has also been added[16].ResultsWe will present the first 3D comparisons between and observations from previous missions.For example, an ongoing study[19] of the Japanese Akatsuki mission's ultraviolet (UV) observations revealed different reflectivity patterns between sulfur dioxide (SO₂) at 283 nm and the unknown UV absorber at 365 nm at low latitudes. The averaged minimum reflectivity at 365 nm occurred ~2 hours earlier in local time than at 283 nm. Our simulations using the Venus PCM (Fig. 1) reveal the presence of a droplet layer situated in the afternoon at low latitude at 70 km, which could mask the unknown UV absorber below and alter the afternoon albedo, explaining the observations made. These droplets are the result of homogeneous nucleation episodes, which are allowed by the chemistry and vertical transport. This highlights the need for 3D simulations in order to understand such processes.Figure 1: Horizontral map of the integrated number of droplets from the top of the atmosphere to a specific altitude (resp. 80,75,70 and 65 km) after 2 venusian days.ReferencesP. Mills, L. W. Esposito, Y. L. Yung, Geophys. Monogr. Ser. 176, 73–100 (2007).R. G. Knollenberg, D. M. Hunten, J. Geophys. Res. 85, 8039–8058 (1980).P. James, O. B. Toon, G. Schubert, Icarus. 129, 147–171 (1997).Imamura, G. L. Hashimoto, J. Geophys. Res. 103, 31349–31366 (1998).Yamamoto, M. Takahashi, J. Geophys. Res. 111, 2006JE002688 (2006).McGouldrick, E. L. Barth, Planet. Sci. J. 4, 50 (2023).Karyu et al., Planet. Sci. J. 5, 57 (2024).Lee, S. R. Lewis, P. L. Read, Icarus. 206, 662–668 (2010).Ando, M. Takagi, N. Sugimoto, H. Sagawa, Y. Matsuda, Journal of Geophysical Research: Planets, in press, doi:10.1029/2019JE006208.Karyu et al., Journal of Geophysical Research: Planets, in press, doi:10.1029/2022JE007595.Stolzenbach, F. Lefèvre, S. Lebonnois, A. Määttänen, Icarus. 395, 115447 (2023).Lebonnois, N. Sugimoto, G. Gilli, Icarus. 278, 38–51 (2016).Gilli et al., Icarus. 281, 55–72 (2017).Guilbon, thesis, Université Paris Saclay (COmUE) (2018).Määttänen, S. Guilbon, J. Burgalat, F. Montmessin, Advances in Space Research. 71,1116–1136 (2023).Streel, thesis, Sorbonne-Université (2025).Määttänen et al., JGR Atmospheres. 123, 1269–1296 (2018).Whitby, F. Stratmann, M. Wilck, Journal of Aerosol Science. 33, 623–645 (2002).R. L. S. E. Aliste Castillo et al., BACO-25 conference abstract (2025).

Ozone is a key trace gas of the Martian atmosphere. It is produced through the photolysis of carbon dioxide followed by a three-body reaction between atomic and molecular oxygen. Its primary sinks are photodissociation, which recycles lighter odd oxygen (Ox) species, and gas-phase reactions with odd-hydrogen (HOx) species, which are produced by water vapour photolysis.Many previous studies have shown that current Mars atmospheric general circulation models (GCMs) fail to reproduce the ozone columns observed by Mars Express and Mars Reconnaissance Orbiter studies (e.g. [1,2]), typically underestimating them by a factor of two [3].To help bridge the gap between models and observations, some studies examined the influence of various factors on the modelled ozone, including heterogeneous chemistry on water ice and dust aerosols, reaction rates, or radiative transfer [1,2]. These adjustments led to some local and temporally limited improvements, but often increased discrepancies elsewhere, suggesting that key processes may still be missing from Martian GCMs.In this study, we adopt a different approach by investigating the propagation of chemical uncertainties using the 1-D sub-model of the Mars Planetary Climate Model (MPCM). We conducted a global sensitivity study using Monte Carlo simulations in which all reaction rates were randomly varied within their measured or estimated uncertainty ranges. Then, we identified correlations between the volume mixing ratios of key species (Ox and HOx) and reaction rates variations, which allowed us to determine which reactions most strongly influenced model outputs. We then adjusted the rates of these key reactions within the full GCM and found that doing so significantly improves simulated ozone VMRs relative to observations from the Atmospheric Chemistry Suite (ACS) onboard the ExoMars Trace Gas Orbiter (TGO). Based on our analysis, we recommend an assessment of these key reaction rates under relevant conditions, along with their implementation in GCMs, to better constrain the remaining discrepancies between models and observations. References:[1] Lefèvre, F., A. Trokhimovskiy, A. Fedorova, L. Baggio, G. Lacombe, A. Määttänen, J.‐L. Bertaux, et al., JGR: Planets 126, no. 4 (2021)[2] Daerden, F., Crowley, J. N., Neary, L., Smith, M. D., Loeffler, M. J., Clancy, R. T., et al., JGR: Planets, 128, (2023)[3] Olsen, K. S., A. A. Fedorova, A. Trokhimovskiy, F. Montmessin, F. Lefèvre, O. Korablev, L. Baggio, et al., JGR: Planets 127, no. 10 (2022)

There exists strong geomorphological, sedimentary and mineralogical evidence that Mars had an active surface hydrological cycle during the Noachian period, about 3.8 Gyr ago (Ga). However, how surface temperatures compatible with perennial liquid water could be sustained in spite of a Sun that only had 75% of its present-day brightness has remained elusive, leading to the faint young Sun paradox for Mars. Recently, the greenhouse effect of hydrogen peroxide (H2O2) has been proposed as a solution by Ito et al. (2020). Radiative transfer models have shown that a few ppmv of H2O2 in a 1 or 2 bar CO2 atmosphere could solve the faint young Sun paradox on early Mars. In a warm and wet CO2 atmosphere, H2O2 is produced by photochemistry and contributes to the stability of the CO2 atmosphere along with the HOx (H, OH and HO2) catalytic cycles. Nevertheless, a thorough assessment of the viability of such a high H2O2 abundance is still lacking. Using 1D and 3D climate models coupled with a C-H-O photochemistry solver, we show that in the most favorable case for H2O2 to build up, its steady-state abundance is several orders of magnitude short from its required abundance of similar to 1 ppmv to have a significant radiative effect. Furthermore, we also show that a transient warming episode associated with massive H2O2 release cannot exceed 10 Martian years. We therefore rule out H2O2 as a warming agent for early Mars.

Venus is home to vivid sulfur chemistry, with as the major sulfur gas species and a global cloud layer between 47 and 70 km composed of and O. The chemistry in the clouds has been extensively studied with 1D models, but none is able to reproduce the three orders of magnitude decrease of inside the clouds. Sulfur allotrope chemistry could be a candidate for buffering sulfur atoms, as it can grow into long chains. Sulfur hydrides such as S is considered as one of the main sulfur-bearing compounds, possibly linked to surface reactions or have a volcanic origin like on Earth. In this study, we use for the first time a 3D model to study the climatology of the sulfur allotrope in gas and condensed phase and hydride chemistry in the clouds with an explicit photolysis calculation and updated UV cross-section. S is close to ppmv levels below the cloud base, the third most abundant sulfur-bearing species in this region after and OCS. Below the clouds, gas phase is the most abundant sulfur allotrope. Above, the photolysis and condensation are preponderant, and the gas phase decreases to extremely low values. Polysulfur can therefore not be the unknown absorber at cloud-top altitudes. The condensed phase polysulfurs are present from 30 to above 100 km. condensed phase is the most abundant due to its low saturation mixing ratios. Polysulfur species represent a substantial sulfur reservoir in the upper cloud, equivalent to a few ppmv.

The stability of Mars's CO2-dominated atmosphere remains incompletely understood because traditional onedimensional photochemical models underestimate atmospheric CO mixing ratios by up to a factor of seven. Here we present the first long-term three-dimensional simulations for long-lived chemical species in the Martian atmosphere using a general circulation model coupled with photochemistry, the Mars Planetary Climate Model, allowing the equilibrium concentration of CO to be determined. When heterogeneous reactions on water-ice clouds and the condensation and surface deposition of H2O2 are included, the model predicts an equilibrium, annually and globally averaged CO volume mixing ratio of 750 ppmv. After correcting for a small underestimation of atmospheric water content relative to observations, the simulated CO mixing ratio becomes 700 ppmv, representing a substantial improvement over previous one-dimensional results and consistent with Earth-based measurements, although still slightly lower than retrievals from multiple satellites orbiting Mars (800-960 ppmv). Sensitivity experiments show that adjusting key chemical reaction rates within up to twice their laboratory-measured uncertainties, or including heterogeneous chemistry on dust particle surfaces, can reproduce the CO mixing ratios measured by the Mars orbiters and in some cases even lead to an overestimation. However, these CO-realistic simulations produce an equilibrium H2 mixing ratio that is substantially higher than observed, converting the long-standing CO-deficit problem in models into a new H2-surplus problem.

Future space missions dedicated to measuring CO2 on a global scale can make advantageous use of the O2 band at 1.27 µm to retrieve the air column. The 1.27 µm band is close to the CO2 absorption bands at 1.6 and 2.0 µm, which allows a better transfer of the aerosol properties than with the usual O2 band at 0.76 µm. However, the 1.27 µm band is polluted by the spontaneous dayglow of the excited state O2(1Δ), which must be removed from the observed signal.We investigate here our quantitative understanding of the O2(1Δ) dayglow with a chemistry-transport model. We show that the previously reported -13% deficit in O2(1∆) dayglow calculated with the same model is essentially due a -20 to -30% ozone deficit between 45-60 km. We find that this ozone deficit is due to excessively high temperatures (+15 K) of the meteorological analyses used to drive the model in the mesosphere.The use of lower analyzed temperatures (ERA5), in better agreement with the observations, slows down the hydrogen-catalyzed and Chapman ozone loss cycles. This effect leads to an almost total elimination of the ozone and O2(1Δ) deficits in the lower mesosphere. Once integrated vertically to simulate a nadir measurement, the deficit in modeled O2(1Δ) brightness is reduced to -4±3%. This illustrates the need for accurate mesospheric temperatures for a priori estimations of the O2(1Δ) brightness in algorithms using the 1.27 µm band.

As part of a long-term monitoring program, full disk thermal maps of HDO (near 7 microns) and SO2 (near 7 and 19 microns) have been obtained at the cloud top of Venus in 2023, using the TEXES(Texas Echelon Cross-Echelle Spectrograph) imaging spectrometer at the Infrared Telescope Facility (IRTF) at Mauna Kea Observatory. Assuming a constant D/H isotopic ratio, the water abundance has been more or less constant since 2018, at about half its value in 2012-2016. In contrast, the SO2 abundance, which was very high in 2018-2019 and very low between July 2021 and March 2023, has increased by a factor of about 5 between February and July 2023 (close to its maximum level of 2018-2019), and has remained at its high level in September 2023. The origin of these long-term variations is still unclear. In addition, stringent upper limits of NH3 (at 927-931 cm-1), PH3 (at 1161-1164 cm-1) and HCN at 744-748 cm-1) at the cloud top have been obtained in July 2023. These results will be presented and discussed.

Due to gravitational perturbations from nearby planets, Mars has undergone large obliquity variations through its history. Modeling suggested that in the past 10 million years, the obliquity of Mars has varied by up to 20°, from 15° to 35°. During time periods of high obliquity, the polar regions of Mars received more solar insolation and became warmer, leading to more rapid sublimation of water ice and higher atmospheric water content. During periods of low obliquity, on the contrary, water vapor condensed in polar regions and the atmosphere became dry. This variation has a significant impact on the photochemistry of the Martian atmosphere, as HOx radicals, which are photolytic products of water vapor, are key catalysts to the photochemistry of the Martian atmosphere. It is then of interest to explore the photochemistry of Mars at different obliquities and its effects on the climate and surface of Mars, as part of the objectives of the “Mars Through Time” European Research Council project. In preparation for future Mars sample return missions, it is important to evaluate the preservability of potential organic matter buried in the shallow subsurface with different oxidizing capacities of the atmosphere at different obliquities. In view of the three-dimensional nature of the sublimation, transport, and condensation of water, we employ a fully coupled photochemical-radiative-dynamical model—the Mars Planetary Climate Model, developed at LMD in collaboration with other institutions—to simulate the photochemistry of the recent Martian atmosphere at obliquities between 15° and 35°. We find that at high obliquities, water content of the Martian atmosphere could exceed the present-day value by more than one order of magnitude, and the OH concentration could be higher by up to two orders of magnitude. These drastic changes result in a significantly lower CO concentration. Opposite effects are observed from low-obliquity simulations. The nonlinearity in the photochemical system, however, has led to more complex behaviors of the HO2 and H2O2 concentrations. We will explain the mechanisms behind these effects and discuss their implications in the paleoclimate of Mars and the preservation of potential biogenic organic matter in the shallow subsurface. We will also address the long-standing “CO-deficit” problem in Mars photochemical modeling, and show how the state-of-the-art 3D photochemical modeling helps to mitigate the problem.

Context. Hydrogen chloride (HCl) was independently detected in the Martian atmosphere by the Nadir and Occultation for MArs Discovery (NOMAD) and Atmospheric Chemistry Suite (ACS) spectrometers aboard the ExoMars Trace Gas Orbiter (TGO). Photochemical models show that using gas-phase chemistry alone is insufficient to reproduce these data. Recent work has developed a heterogeneous chemical network within a 1D photochemistry model, guided by the seasonal variability in HCl. This variability includes detection almost exclusively during the dust season, a positive correlation with water vapour, and an anticorrelation with water ice. Aims. The aim of this work is to show that incorporating heterogeneous chlorine chemistry into a global 3D model of Martian photochemistry with conventional gas-phase chemistry can reproduce spatial and temporal changes in hydrogen chloride on Mars, as observed by instruments aboard the TGO. Methods. We incorporated this heterogeneous chlorine scheme into the Mars Planetary Climate Model (MPCM). After some refinements to the scheme, mainly associated with it being employed in a 3D model, we used it to model chlorine photochemistry during Mars Years (MYs) 34 and 35. These two years provide contrasting dust scenarios, with MY 34 featuring a global dust storm. We also examined correlations in the model results between HCl and other key atmospheric quantities, as well as production and loss processes, to understand the impact of different factors driving changes in HCl. Results. We find that the 3D model of Martian photochemistry using the proposed heterogeneous chemistry is consistent with the changes in HCl observed by ACS in MY 34 and MY 35, including detections and 70% of non-detections. For the remaining 30% of non-detections, model HCl is higher than the ACS detection limit due to biases associated with water vapour, dust, or water ice content at these locations. As with previous 1D model calculations, we find that heterogeneous chemistry is required to describe the loss of HCl, resulting in a lifetime of a few sols that is consistent with the observed seasonal variation in HCl. As a result of this proposed chemistry, modelled HCl is correlated with water vapour, airborne dust, and temperature, and anticorrelated with water ice. Our work shows that this chemical scheme enables the reproduction of aphelion detections in MY 35.A

About 30 tonnes of cosmic dust particles – mostly from Jupiter Family Comets - enters Venus’ atmosphere every (Earth) day, of which around 40% ablates. This causes the injection of various metals (Fe, Mg, Si and Na in particular) into the atmosphere between 105 and 125 km. By analogy with the Earth, these metals should provide important tracers of both chemistry and atmospheric dynamics. In order to guide future observations of these metals, both from terrestrial telescopes and spacecraft, we have developed detailed chemical networks for each of the elements. These networks are extensions of those used to model these metals in the terrestrial atmosphere, where the Fe, Mg and Na networks have been rigorously tested against observations of neutral and ionized metal atoms made with ground-based lidars, spaceborne spectrometers, and sub-orbital rockets. For Venus, we now include a detailed chlorine chemistry because of the very large concentration of HCl produced by volcanic emissions. Where reactions have not been studied in the laboratory, we have employed quantum chemistry calculations combined with master equation rate theory for reactions taking place on multi-well potential energy surfaces. These networks were then inserted into the global Venus Planetary Climate Model. The simulations reveal that the metal atoms occur in layers about 10 km wide which peak around 110 km, and the metal ion layers peak about 10 km higher. Below 105 km the metals form carbonates, which are then converted into chlorides by reaction with HCl emitted by surface volcanoes. In this presentation we will discuss the metal layer variability on the day- and night-side, and the feasibility of detecting Mg, Mg+ and Na by observing solar-pumped resonance fluorescence on the dayside, and Na chemiluminescence on the night-side.

HDO is an isotopic form of water that can provide clues about the history and evolution of water on terrestrial planets. By comparing the D/H ratio derived from the abundance ratio of HDO and H2O on Venus with that of other planets or comets that have similar origins, we can estimate how much water Venus stored and lost during its formation and evolution. The Venus Plobal Climate Model (VPCM) developed by several laboratories (LMD, LATMOS) of Institute Pierre-Simon Laplace (IPSL, in Paris area) can simulate the chemical and dynamical processes of the Venusian atmosphere. However, HDO has so far not been included in the VPCM before. In this work, we first implement HDO in the gas and liquid phases as two additional tracers of the model to investigate their spatial and temporal distributions. As an isotope of water, HDO participates to all the chemical and physical processes in which water is involved. Furthermore, we have analyzed the influence of fractionation of HDO during condensation, and photolysis processes on the resulting D/H.

It is still unknown how much water has escaped from Mars during its history. Hydrogen escape from Mars's atmosphere probably played a major role in drying the planet, but present-day Hloss rates (about 3x10^26 atoms per second on average) cannot explain the geological evidence for the large volumes of liquid water on ancient Mars. Here we used the three-dimensional Mars-Planetary Climate Model to show that H loss rates could have increased by more than one order of magnitude (6x10^27 atoms per second) during higher spin axis obliquity periods, notably in the last few million years when Mars's obliquity was about 35 deg on average. The resulting accumulated H escape over Mars's history translates into an approx. 80 m global equivalent layer, which is close to the lower limit of geological estimates, assessing the major role of atmospheric escape in drying Mars.

It has been proposed that two isomers of the SO dimer (cis- and trans-OSSO) are candidates for the unknown UV absorber in Venus' atmosphere because they have a good spectral match with the absorber, despite the low concentrations predicted by 1D photochemical models. Here OSSO chemistry (production from SO and loss by photolysis, thermal decomposition, and reaction with O and Cl) has been included in the photochemistry scheme of a 3D planetary climate model (PCM-Venus) along with sulfur injection due to meteoric ablation. 1D multiple scattering radiative transfer modeling is then used to predict the resulting top-of-the-atmosphere reflectance produced by OSSO. The modeled OSSO concentrations are shown to be similar to 3 orders of magnitude too low to explain the observed absorbance levels, and the predicted ratio of the OSSO isomers provides an unsatisfactory match to the spectral shape of the unknown absorber.

We performed retrievals of dust and water-ice optical depths at select times spanning Mars years (MYs) 33 through 36. We used data taken by the Imaging Ultraviolet Spectrograph (IUVS) instrument aboard the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft, whose precessing orbit allowed IUVS to image the diurnal evolution of water-ice clouds at local times throughout this MY range where they have not been studied. We created a radiative-transfer retrieval algorithm and used it to simultaneously fit the dust and water-ice optical depth of each usable spectrum in IUVS apoapse data for the majority of the MAVEN mission. We compared our results to other datasets to ensure our retrievals produced plausible values and discuss potential reasons for discrepancies. We obtained global climate model (GCM) simulations from two state-of-the-art models and compared our results to both sets of simulations. We show that there are significant differences between our water-ice retrievals and both sets of simulations, both in the spatial cloud patterns and column-integrated optical depths. We discuss the different approaches both models used for simulating these clouds and the implications for accurately modeling these clouds in future GCM work.

The ExoMars Trace Gas Orbiter (TGO) mission had started regular measurements in 2018. Primary goal of the mission is to quantify trace gases that could indicate geologic or biogenic activity on Mars (Vago et al., 2015). Atmospheric Chemistry Suite mid-infrared channel (ACS MIR) is a high resolution cross-dispersion spectrometer operating in solar occultation mode (Korablev et al., 2018). It was designed to make the most sensitive measurements of the atmosphere to date. During each occultation up to 20 diffraction orders are simultaneously recorded at different tangent altitudes. In 2020 ACS MIR reports the discovery of the gaseous hydrogen chloride (HCl). Absorption features are present in several consecutive diffraction orders, withal both isotopes H37Cl and H35Cl are clearly observed. HCl was observed by ACS simultaneously in both hemispheres after the main phase of the global dust storm. Though the formation mechanism is not fully clear, we believe that the presence of HCl is associated with the lifted dust and chlorine component in it.On Earth, in general, the chlorine isotope variations in nature are relatively small, ranging from ~-2 to +2 ‰. However, large variations are observed, e.g. in extraterrestrial materials and volcanic gases, due to kinetic fractionation. On Mars Farley et al. (2016) reported a range from -1 ‰ to −51 ‰ (5% reduction) for the δ37Cl in the samples drilled in the Gale Crater. ACS observations demonstrate enrichment of the 37Cl up to +250 ‰ on average in the atmospheric gaseous. In principle, most atmospheric elements on Mars have heavy isotope enrichments due to preferential loss of the light isotope to space (e.g. Vandaele et al., 2019). Early hydrodynamic escape during intense extreme ultraviolet radiation followed by prolonged atmospheric ‘erosion’ explains the heavy isotope enrichment. Chlorine loss, as HCl, would raise the δ37Cl value of the residual materials, involved in the dust-atmospheric exchange cycle. ReferencesFarleya K.A., Martina P., Archer P.D. , et al.: Light and variable 37Cl/35Cl ratios in rocks from Gale Crater, Mars: Possible signature of perchlorate, Earth and Planetary Science Letters 438:14-24, DOI: 10.1016/j.epsl.2015.12.013, 2016.Korablev, O., Montmessin, F., Trokhimovskiy, et al..: The Atmospheric Chemistry Suite (ACS) of Three Spectrometers for the ExoMars 2016 Trace Gas Orbiter, Space. Sci. Rev., 214(1), 7, doi:10.1007/s11214-017-0437-6, 2018.Vago, J., Witasse, O., Svedhem, et al.: ESA ExoMars program: The next step in exploring Mars, Sol. Syst. Res., 49(7), 518–528, doi:10.1134/S0038094615070199, 2015.Vandaele, A. C., Korablev, O., Daerden, F. et al.: Martian dust storm impact on atmospheric H2O and D/H observed by ExoMars Trace Gas Orbiter, Nature, 568, 521–525, doi:10.1038/s41586-019-1097-3, 2019.

In 2020, hydrogen chloride (HCl) in the gas phase was discovered in the atmosphere of Mars with the Atmospheric Chemistry Suite (ACS) onboard the Trace Gas Orbiter (TGO) mission (Korablev et al., 2021). Its volume mixing ratio (VMR) shows a seasonal increase of up to 5 ppbv during the perihelion season, followed by a sudden drop to undetectable levels, contradicting modelling estimates of the HCl lifetime of several months. In the Earth's stratosphere, heterogeneous uptake of HCl onto water ice is known to be a major sink for this species. This reaction is now also considered when modelling HCl abundances in the Martian atmosphere. In this work, we use simultaneous measurements of water ice and HCl obtained by the ACS instrument to find particular structures in the vertical profiles as detached gas layers at ice-free altitudes (“ice-holes”). From these particular examples we conclude that the heterogeneous uptake of HCl onto water ice operates on Mars and is a fast mechanism regulating the HCl abundance in the atmosphere of Mars.

. IntroductionVenus is hosting a global sulfuric acid cloud layer between 45 and 70 km which has been investi- gated by the Venus Express and Akatsuki mission as well as its coupling with the surface. One of the main questions that remains unclear about the dynamics of the Venusian atmosphere is how this convective cloud layer mixes momentum, heat, and chemical species and generates gravity waves. Several models have been developed to study these phenomenons. We proposed to use these models to study the impact of this turbulence on the chemical species, focusing on water and sulfuric dioxide.2. ModelTo study the convective layer, a Large Eddy Simulations (LES) model [1] has been developed using the Weather-Research Forecast (WRF) non-hydrostatic dynamical core [2] coupled with the IPSL Venus GCM physics package [3]. The model is able to resolve a realistic convective layer between 47 and 55 km as well as one convective layer at cloud top altitudes (70 km) at the substellar point (Fig 1).Figure 1: Vertical cross-section of the vertical wind (m/s) at the Equator at noon. Between 47 and 55 km is the main convective layer, between 55 and 67 km are the gravity waves induced by convection and between 67 and 73 is the cloud top convective layer presents only at the substellar point.Tracers has been included in the model representing H2O and SO2, the chemistry and photodissociation sources and sinks are modeled by a linear relaxation of the tracer abundance toward a prescribed vertical profile with a characteristic time. The relaxation time ranges from 102 to 106 s. The prescribed vertical tracer profiles are constructed using observed abundance visible in Fig 2.Figure 2: Vertical profile of the tracer abudance relaxation profile. The black represents the value for the deep atmosphre [4], the star is the SO2 ground based observations at 65 km [5] and the circle is the cloud top H2O Venus Express value [6, 7].3. ResultsThis simple model is able to determine the vertical mixing for SO2 and H2O in the cloud layer, and for which chemical timescale the convection plays an important role. The resolution of 500 m allow an estimate of the horizontal turbulent spatial features, induced by the convection and gravity waves, for SO2 and H2O.References[1] Lefèvre et al., JGR : Planets, 123, 2773-2789, 2018.[2] Skamarock, W. C. and J. B. Klemp, J., Comput. Phys., 227, 3465-3485, 2008[3] Garate-Lopez, I. and Lebonnois., S., Icarus, 314,1-11, 2018.[4] Bézard, B. and De Bergh, C., JGR : Planets, 112, 2007.[5] Encrenaz, T. et al., A. & A., 595, 2016.[6] Fedorova, A. et al., Icarus, 275, 143-162, 2016.[7] Cottini., V. et al., Icarus, 217, 561-569, 2012.

The annual formation of an ozone hole in the austral spring has regional and global climate implications. The Antarctic ozone hole has already changed the precipitation, temperature and atmospheric circulation patterns, and thus the surface climate of many regions in the Southern Hemisphere (SH). Therefore, the study of ozone loss variability is important to assess its consequential effects on the climate and public health. Our study uses satellite observations from the Microwave Limb Sounder on Aura and the passive-tracer method to quantify the ozone loss for the past 8 years (2013–2020) in the Antarctic. We observe the highest ozone loss (about 3.5 ppmv) in 2020, owing to the high chlorine activation (about 2.2 ppbv), steady polar vortex, and huge expanses of polar stratospheric clouds (PSCs) (12.6×106 km2) in the winter. The spring of 2019 also showed a high ozone loss, although the year had a rare minor warming in mid-September. The chlorine activation in 2015 (1.9 ppbv) was the weakest, and the wave forcing from the lower latitudes was very high in 2017 (up to −60 km s−1). The analysis shows significant interannual variability in the Antarctic ozone as compared to the immediate previous decade (2000–2010). The study helps to understand the role of dynamics and chemistry in the interannual variability of ozone depletion over the years.