Periodic Reporting for period 1 - MuSICA-V (Multi-Scale Investigation of the Chemistry of the Atmosphere of Venus)
Reporting period: 2023-12-01 to 2025-11-30
Summary of the context and overall objectives of the project
Venus is the closest planet to Earth. Despite a similar size and mass, there are differences between the two planets. At the surface, the temperature can reach 730 K with pressure of 90 bar, and a composition of 96 % of carbon dioxide. Venus hosts a global cloud layer between 45 and 70 km of altitude, with composition and temperature-pressure conditions close to the Earth's stratosphere and complex chemistry with both sulphur and water cycle. This global cloud layer plays a key role in the radiative equilibrium of the atmosphere. Therefore, it is fundamental to study its composition and dynamics at all spatio-temporal scales to understand the atmosphere of Venus. Despite decades of measurements and modelling, there are still many unknowns about the chemistry of the Venusian atmosphere.
The Project MuSICA-V (Multi-Scale Investigation of the Chemistry of the Atmosphere of Venus) conducted at LATMOS will develop new and ambitious numerical models using a hierarchy of models: a Planetary Climate Model (PCM),
mesoscale and Large-Eddy Simulation (LES) models all coupled to a photochemistry scheme. These three models are performed with different resolutions and would help capture the spatio-temporal variability of the chemistry over different scales as never before, and will increase the understanding of the coupling of the dynamics and chemistry from the large-scale to the small-scales.
The proposed effort is perfectly timed and relevant to ongoing and planned international Venus exploration activities: ESA mission EnVision, and NASA missions DAVINCI and VERITAS, were all three selected to launch in the next
decade. The main objectives of these missions are to study the surface and the dynamics both inside and below the clouds. The project will simulate predictions for chemistry variabilities to produce observables for past and future missions, to improve the interpretation of the measurements.
The MuSICA-V project is built around four scientific axes. The first three axes relate to the development of numerical tools with a hierarchy of models, and the last one pertains to the new analyses of the Venus Express data and helping future missions in chemistry predictions of their observables.
The MuSICA-V project will allow me to acquire broad expertise in the science of Venus and clouds, increasing my knowledge of atmospheric numerical simulations, as well as bringing me new expertise in modelling atmospheric chemistry and spectroscopic remote-sensing targeting different altitudes and scientific objectives and directly linked to a space mission. Chemistry is one of the main focuses of the future selected Venus missions, to constrain the possible active volcanism, and to study the surface/atmosphere interaction and the coupling of the dynamics and the chemistry. The project MuSICA-V will develop new tools to investigate the chemistry of Venus. The chemistry of the Venusian atmosphere was almost exclusively studied with 1D models and not often in 3D. The Venusian tropospheric chemistry was never modelled in 3D. The impact of atmospheric turbulence on chemistry has never been studied. The models developed with the MuSICA-V project will give an unprecedented insight into the Venus atmospheric chemistry from the surface to cloud-top altitude, and from the small to large-scale, will be a useful tool for the planetary science community. The models developed during this project could be then used to assess the feasibility of future missions. With a better knowledge of Venus' current state, the species abundance in the atmosphere, and their reservoir buffered in the surface rocks, it would be possible to understand the evolution of Venus and to know why the climates of Earth and Venus are so different. The characterization of the present-day Venus climate also has an interest in the context of habitability. With current telescopes, distinguishing an exo-Earth planet from an exo-Venus is challenging. The understanding of the coupling of the dynamics with chemistry and clouds would increase the capacity to differentiate between the two types of climate.
The Project MuSICA-V (Multi-Scale Investigation of the Chemistry of the Atmosphere of Venus) conducted at LATMOS will develop new and ambitious numerical models using a hierarchy of models: a Planetary Climate Model (PCM),
mesoscale and Large-Eddy Simulation (LES) models all coupled to a photochemistry scheme. These three models are performed with different resolutions and would help capture the spatio-temporal variability of the chemistry over different scales as never before, and will increase the understanding of the coupling of the dynamics and chemistry from the large-scale to the small-scales.
The proposed effort is perfectly timed and relevant to ongoing and planned international Venus exploration activities: ESA mission EnVision, and NASA missions DAVINCI and VERITAS, were all three selected to launch in the next
decade. The main objectives of these missions are to study the surface and the dynamics both inside and below the clouds. The project will simulate predictions for chemistry variabilities to produce observables for past and future missions, to improve the interpretation of the measurements.
The MuSICA-V project is built around four scientific axes. The first three axes relate to the development of numerical tools with a hierarchy of models, and the last one pertains to the new analyses of the Venus Express data and helping future missions in chemistry predictions of their observables.
The MuSICA-V project will allow me to acquire broad expertise in the science of Venus and clouds, increasing my knowledge of atmospheric numerical simulations, as well as bringing me new expertise in modelling atmospheric chemistry and spectroscopic remote-sensing targeting different altitudes and scientific objectives and directly linked to a space mission. Chemistry is one of the main focuses of the future selected Venus missions, to constrain the possible active volcanism, and to study the surface/atmosphere interaction and the coupling of the dynamics and the chemistry. The project MuSICA-V will develop new tools to investigate the chemistry of Venus. The chemistry of the Venusian atmosphere was almost exclusively studied with 1D models and not often in 3D. The Venusian tropospheric chemistry was never modelled in 3D. The impact of atmospheric turbulence on chemistry has never been studied. The models developed with the MuSICA-V project will give an unprecedented insight into the Venus atmospheric chemistry from the surface to cloud-top altitude, and from the small to large-scale, will be a useful tool for the planetary science community. The models developed during this project could be then used to assess the feasibility of future missions. With a better knowledge of Venus' current state, the species abundance in the atmosphere, and their reservoir buffered in the surface rocks, it would be possible to understand the evolution of Venus and to know why the climates of Earth and Venus are so different. The characterization of the present-day Venus climate also has an interest in the context of habitability. With current telescopes, distinguishing an exo-Earth planet from an exo-Venus is challenging. The understanding of the coupling of the dynamics with chemistry and clouds would increase the capacity to differentiate between the two types of climate.
Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far
WP 1: Suflur cloud chemistry
The Large-Eddy Simulation (LES) was successfully coupled to the Planetary Climate Model (PCM). This is the first model of its kind for Venus. This study confirms that species such as SO2, with a lifetime longer than the characteristic convection time, are well mixed vertically between 48 and 55 km. The chemical lifetime of the species will also influence spatial and temporal variability in the convective region. A well-mixed species will have low variability. Convection will also increase the optical thickness of the cloud. The estimated mixing calculated is consistent with in situ estimates, and much greater than the values frequently used in chemical models. I was also able to estimate for the first time the impact of turbulent activity on the altitude of the floor and top of the cloud layer. Convection and gravity waves will cause the cloud to shift between 200 m and 1 km. These simulations will be used to quantify the observability of fine-scale processes for the VenSpec-u spectrometer aboard EnVision.
The sulfur allotrope chemistry has been successfully implemented in the Planetary Climate Model. This is first a 3D model for Venus 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. H2S is close to ppmv levels below the cloud base, the third most abundant sulfur-bearing species in this region after SO2 and OCS. Below the clouds, S8 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. S2 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.
WP2: Chemistry of the troposphere
Following the implementation of the sulfur allotrope chemistry, high temperature chemical reactions were successfully implemented in the PCM. Simulations are ongoing and would allow unprecedented view of chemistry in the troposphere. Significant changes are seen in 3D simulations compared to 1D, therefore the role of horizontal transport is determined for the first time.
The first mesoscale modelling was developed to study the near-surface winds on Venus. A change of direction is occurring during the day in the main slopes, with upslope winds at noon due to solar heating and downslope winds at night. This is due to efficient IR cooling of the surface during the night, being colder than its surroundings slope atmospheric environment and leading to displacement of air. The temperature is impacted by the adiabatic cooling/warming induced by those winds. A strong heating effect is occurring for the downslope winds, leading to an anti-correlation between the surface temperature diurnal amplitude and the topography. This diurnal amplitude reaches 4~K in the plains and below 1~K in the mountains. The saltation of sediment by those winds was also quantified, with a higher probability at night along the slopes on the western flanks. Such models will help to study the transport of the chemical species and dust near the surface.
WP3: Modelling of volcanic plumes
Past modelling efforts have only studied explosive volcanic plume propagation over a limited range of flow parameters at the vent and in an idealised Venus atmospheric configuration. The 1D FPLUME volcanic plume model was successfully adapted in a realistic Venusian environment. In similar Venusian conditions, the height of the plume is consistent with past modelling. The present study shows that explosive volcanism would preferably reach 15 km of altitude. Under certain conditions, plumes are able to reach the VenSpec-H tropospheric altitude range of observations and even the 45 km cloud floor. For the first time, the impact of wind was quantified, and the super-rotating winds have a substantial impact by plume-bending of reducing the height of plumes. Contrary to the Earth, the atmospheric heat capacity depends greatly on temperature, and will disadvantage lower plumes and allow larger plumes to propagate at higher altitudes. The high latitude atmospheric environment, due to the thermal profile and weaker winds, is favorable to plumes reaching higher altitudes.
The 3D volcanic plume model ASHEE was successfully adapted in a realistic Venusian environment. Simulations are ongoing and would allow unprecedented view of the vertical propagation of volcanic in the Venusian environment.
WP 4: Observability with the VenSpec instruments and a revisit of previous data
The LES model developed in WP1 is used to compute maps of atmospheric parameters related to VenSpec-U’s science goals; a Radiative Transfer Model (RTM), initially developed for the SPICAV/Venus Express data analysis and adapted for VenSpec-U, translates these parameters into spectral radiance maps; and a newly developed Instrument Forward Model simulates the optics and detector effects as well as onboard data processing steps. By modifying the maps of RTM parameters, the contrasts limits below which the small-scale variations of the atmospheric properties were assessed and can no longer be retrieved accurately. These thresholds under various conditions, including different latitudes, spacecraft altitudes, and spatial samplings were evaluated. These detection limits appear in accordance with the expected performances.
The modelling effort in WP3 was used by the Planetary Spectrum Generator to simulate the nightside thermal emission window of Venus in order to quantify the observability of volcanic plume by VenSpec-H. The effect of a volcanic gas plume rising to a ceiling altitude, for species such as HO, CO, OCS, HF and SO was simulated. The sensitivity of the radiance spectrum at different wavelengths was explored as an attempt to qualitatively access detection for future measurements of both ground-based and space-instrumentation. Qualitative analysis concludes that for the HO, CO and OCS plumes simulated there is potential to achieve a detection in the future, given a minimum required signal-to-noise ratio of 50. For SO and HF plumes, a higher signal-to-noise ratio would be needed.
The Large-Eddy Simulation (LES) was successfully coupled to the Planetary Climate Model (PCM). This is the first model of its kind for Venus. This study confirms that species such as SO2, with a lifetime longer than the characteristic convection time, are well mixed vertically between 48 and 55 km. The chemical lifetime of the species will also influence spatial and temporal variability in the convective region. A well-mixed species will have low variability. Convection will also increase the optical thickness of the cloud. The estimated mixing calculated is consistent with in situ estimates, and much greater than the values frequently used in chemical models. I was also able to estimate for the first time the impact of turbulent activity on the altitude of the floor and top of the cloud layer. Convection and gravity waves will cause the cloud to shift between 200 m and 1 km. These simulations will be used to quantify the observability of fine-scale processes for the VenSpec-u spectrometer aboard EnVision.
The sulfur allotrope chemistry has been successfully implemented in the Planetary Climate Model. This is first a 3D model for Venus 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. H2S is close to ppmv levels below the cloud base, the third most abundant sulfur-bearing species in this region after SO2 and OCS. Below the clouds, S8 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. S2 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.
WP2: Chemistry of the troposphere
Following the implementation of the sulfur allotrope chemistry, high temperature chemical reactions were successfully implemented in the PCM. Simulations are ongoing and would allow unprecedented view of chemistry in the troposphere. Significant changes are seen in 3D simulations compared to 1D, therefore the role of horizontal transport is determined for the first time.
The first mesoscale modelling was developed to study the near-surface winds on Venus. A change of direction is occurring during the day in the main slopes, with upslope winds at noon due to solar heating and downslope winds at night. This is due to efficient IR cooling of the surface during the night, being colder than its surroundings slope atmospheric environment and leading to displacement of air. The temperature is impacted by the adiabatic cooling/warming induced by those winds. A strong heating effect is occurring for the downslope winds, leading to an anti-correlation between the surface temperature diurnal amplitude and the topography. This diurnal amplitude reaches 4~K in the plains and below 1~K in the mountains. The saltation of sediment by those winds was also quantified, with a higher probability at night along the slopes on the western flanks. Such models will help to study the transport of the chemical species and dust near the surface.
WP3: Modelling of volcanic plumes
Past modelling efforts have only studied explosive volcanic plume propagation over a limited range of flow parameters at the vent and in an idealised Venus atmospheric configuration. The 1D FPLUME volcanic plume model was successfully adapted in a realistic Venusian environment. In similar Venusian conditions, the height of the plume is consistent with past modelling. The present study shows that explosive volcanism would preferably reach 15 km of altitude. Under certain conditions, plumes are able to reach the VenSpec-H tropospheric altitude range of observations and even the 45 km cloud floor. For the first time, the impact of wind was quantified, and the super-rotating winds have a substantial impact by plume-bending of reducing the height of plumes. Contrary to the Earth, the atmospheric heat capacity depends greatly on temperature, and will disadvantage lower plumes and allow larger plumes to propagate at higher altitudes. The high latitude atmospheric environment, due to the thermal profile and weaker winds, is favorable to plumes reaching higher altitudes.
The 3D volcanic plume model ASHEE was successfully adapted in a realistic Venusian environment. Simulations are ongoing and would allow unprecedented view of the vertical propagation of volcanic in the Venusian environment.
WP 4: Observability with the VenSpec instruments and a revisit of previous data
The LES model developed in WP1 is used to compute maps of atmospheric parameters related to VenSpec-U’s science goals; a Radiative Transfer Model (RTM), initially developed for the SPICAV/Venus Express data analysis and adapted for VenSpec-U, translates these parameters into spectral radiance maps; and a newly developed Instrument Forward Model simulates the optics and detector effects as well as onboard data processing steps. By modifying the maps of RTM parameters, the contrasts limits below which the small-scale variations of the atmospheric properties were assessed and can no longer be retrieved accurately. These thresholds under various conditions, including different latitudes, spacecraft altitudes, and spatial samplings were evaluated. These detection limits appear in accordance with the expected performances.
The modelling effort in WP3 was used by the Planetary Spectrum Generator to simulate the nightside thermal emission window of Venus in order to quantify the observability of volcanic plume by VenSpec-H. The effect of a volcanic gas plume rising to a ceiling altitude, for species such as HO, CO, OCS, HF and SO was simulated. The sensitivity of the radiance spectrum at different wavelengths was explored as an attempt to qualitatively access detection for future measurements of both ground-based and space-instrumentation. Qualitative analysis concludes that for the HO, CO and OCS plumes simulated there is potential to achieve a detection in the future, given a minimum required signal-to-noise ratio of 50. For SO and HF plumes, a higher signal-to-noise ratio would be needed.
Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)
Chemistry is one of the main focuses of the future selected Venus missions, to constrain the possible active volcanism, and to study the surface/atmosphere interaction and the coupling of the dynamics and the chemistry. The project MuSICA-V developed new tools to investigate the chemistry of Venus. For the first time, the impact of atmospheric turbulence on chemistry and the polysulfur chemistry were studied in 3D. The vertical propagation of volcanic plumes in Venus atmosphere was assessed with a realistic model. The different models developed with the MuSICA-V project gave an unprecedented insight into the Venus atmospheric dynamics and chemistry from the surface to cloud-top altitude, and from the small to large-scale, and is a useful open-access tool for the planetary science community. The models developed during this project were already used to assess the feasibility of future missions. Other usage of these models are planned for the future missions. The study of the Venusian tropospheric chemistry is still ongoing, and would allow the study of the chemical interaction between the surface and the atmosphere.