The discovery of the mass-independent isotopic fractionations of sulfur and oxygen (S-MIF and O-MIF) has revolutionized the way fundamental geochemical questions are addressed and have produced one of the most iconic figures in geosciences, i.e. the presence of S-MIF in rocks older than 2.3 billion years and its sudden quasi disappearance thereafter. Regarding O-MIF, the majority of the anomalies observed on Earth originate from the ozone anomaly transferred to oxygen-bearing molecules. Although there are still uncertainties pertaining to the mechanisms of O-MIF transfers, they tend to pale into insignificance when compared to those on the exact processes creating S-MIF. There is now no general consensus on the origin of S-MIF in the atmosphere and all the proposed mechanisms are still highly debated in geosciences. Recently NASA has identified the resolution of the origin of S-MIF as one of the top priorities for its astrobiology program, recognizing the importance of MIF in solving the epic question of the origin of life and its interaction with the planetary environment. The identification and quantitative understanding of processes involved in creating and transferring MIF anomalies, a prerequisite for extracting the information embedded in isotopic data, would certainly lead to major advances in our comprehension of the geochemical and environmental evolution of our Earth, from its most primitive existence to the present day. In this project, we propose a multidisciplinary approach to re-examine the sources of MIF in sulfates using an integrated program of novel laboratory experiments, dedicated field studies and innovative multi-scale atmospheric photochemical modeling (including both O- and S-MIF as prognostic variables). First, using the successful isotopic methodology applied to sulfate from polar snow and ice core, we will assess the potential of sulfate leached from volcanic ash as tracers of atmospheric oxidation processes. Second, we plan to carry out a new set of chamber experiments on SO2-related production of S-MIF considering environmental conditions that are as close as possible to those of the stratosphere and of the presupposed Archean atmosphere. Third, for the first time, S-MIF and O-MIF isotope chemistry schemes will be coupled and implemented in models (i.e. a photochemical box/plume model and a global chemistry-transport model). As O-MIF has already largely demonstrated its capacity to probe sulfur oxidation mechanisms in the atmosphere, combining O-MIF and S-MIF analysis should represent a powerful approach to constrain better inferences on the origin of S-MIF. One of the aims is to improve our quantitative understanding of oxidation processes of volcanic and anthropogenic sulfur, and of the resulting production of aerosols. We will also assess the potential of this innovative approach for probing atmospheric chemistry in the distant past. Overall, by providing a much more robust basis for quantitative inferences from S-MIF and O-MIF data, the project will yield new constraints on fundamental questions regarding the late oxygenation of the atmosphere, the shift from an anaerobic to aerobic environment for life, and the reconstruction of the impact of volcanic eruptions and human activities on atmospheric oxidizing capacity and climate.

Improving our knowledge of the atmospheric water cycle requires vertical measurements resolved in time space of the two main water vapor stable isotopes relative abundance in the lower and mid-troposphere. We aim at meeting this challenge with a high sensitivity differential absorption LIDAR instrumentation, which will allow to fill the undeniable lack of observable data, in order to increase the accuracy of climate models. For this purpose the SWALIDE project proposes to combine state-of-the-art infrared detection technologies based on HgCdTe avalanche photodiodes with the first differential absorption lidar system WAVIL dedicated to the measurement of water vapor isotopic abundance. The first objective is to bring the lidar to an enhanced level of sensitivity for atmospheric science and future observation networks applications. For this, a specific avalanche photodiode with an original monolithic architecture will be developed to provide a breakthrough in terms of sensitivity and operability. To support this objective, the whole instrumentation will be tested and validated by inter-comparisons with other sensors such as industrial spectrometers designed for in situ measurements. The second objective is in line with future space lidar missions, which will extend the observations of water vapor and isotopic abundance to the global scale in order to build an unprecedented climatology of convergence and divergence zones of humidity in the atmosphere. For this purpose, the avalanche photodiode, its amplification and formatting electronics will be designed and built in collaboration with Airbus DS. This will prepare the spin-out of research to industry for future lidar missions that may be proposed by France to the European Space Agency with the support of CNES.

Extreme heavy precipitation events (HPEs) pose a threat to human life but remain difficult to predict. Considerable efforts to improve the skill of the forecasts for such severe events have been made in recent years and significant progress has been realized through the development of convection-permitting numerical weather prediction systems (NWPS). However, our ability to predict such high-impact events remains limited because of the lack of adequate high frequency, high resolution water vapor (WV) observations in the low troposphere (below 3 km). HPEs occurring in small and steep watersheds are responsible for the triggering of flash floods with a sudden and often violent onset and rapid rising time, typically from 1 to 6 h following the causative rainfall. We aim to implement an integrated prediction tool, coupling network measurements of WV profiles and a numerical weather prediction model to precisely estimate the amount, timing and location of rainfall associated with HPEs in southern France (struck by ~7 HPEs per year during the fall). The proposed WaLiNeAs project is a unique, innovative initiative that will for the first time ever allow assimilating high vertical resolution lidar-derived WV profiles in the first 3 km of the troposphere. The benefit of WaLiNeAs to the academic and operational communities is dual: advance knowledge of the complex dynamical and dynamical processes controlling the life cycle of HPEs and enhance the predictability of HPEs in southern France at scales relevant for meteorological studies. Both aspects are dealt with in the framework of WaLiNeAs. A network of 5 autonomous Raman WV lidars will be deployed in the Western Mediterranean to provide measurements with high vertical resolution and accuracy, closing critical gaps in lower troposphere WV observations by current operational networks and satellites. Near real-time processing and ensemble assimilation of the WV data in the French operational Application of Research to Operations at MEsoscale (AROME) model, using a 4DEnVar approach with 15 min updates, is expected to enhance the model capability for kilometer-scale prediction of HPEs over southern France 48 hours in advance. The field campaign is scheduled to start early September 2022, to cover the period most propitious to heavy precipitation events in southern France. The Raman WV lidar network will be operated by a consortium of French, German and Italian research groups. Lidar data will be made available to Météo-France shortly after being acquired up to 96 times per day. Besides demonstrating the potential of WV lidar data assimilation in a near real-time operational context, an ancillary objective of the project is also to show that Raman lidars can be left to operate continuously almost unattended for a period of at least 3 months. It is a prerequisite in the perspective of future deployment of operational Raman lidar systems meant to fulfil the observational gaps in WV in the lower troposphere of the current operational observation networks and satellites. This project will lead to recommendations on the lidar data processing for future operational exploitation in NWPS. This project will contribute significantly to the scientific objectives of CES04 « Innovations scientifiques et technologiques pour accompagner la transition écologique » through the development of all-weather, unattended, continuous operation of Raman lidar systems for smart monitoring of the environment, and WV in particular. This project is highly innovative and will lay the foundation for a future integrated warning tool aiming to prevent natural hazards associated with heavy precipitation events as often experienced along the Mediterranean coastline. Once the proof of concept is validated in the framework of the WaLiNeAs project, similar integrated tools may be applied in other parts of the World to avoid similar natural hazards.

MECCOM is a fundamental research project on the formation of carbon dioxide (CO2) clouds of planet Mars that aims at realizing the first ever modeling at all scales (from microphysical to global) of these exotic clouds. They form out of the main constituent of the Martian atmosphere in the winter poles in the troposphere and in the mesosphere at tropical latitudes. Second only to Earth’s atmosphere, Martian atmosphere is among the most observed atmospheres in our Solar System, yet these clouds were only detected in the turn of last century. Thus, their formation is no more a myth; however, they still hold on to their mysteries at all scales. Their impact in the global CO2 cycle has not been quantified, their complex dynamical nature within the polar night, and also in the mesosphere, remains to be elucidated. In addition, the key to their formation in the mesosphere, the ice nuclei available above 40 km altitude, is still searched for. The formation of clouds in a near-pure vapor has obliged us to revisit the used microphysical theories, in particular concerning condensation and sublimation. The MECCOM team has been involved in studying the CO2 clouds since their discovery on both the observational and modeling fronts, and the team members are international leaders on this topic. Now the team has access to a set of models, developed in-house and in tight collaboration, ranging from detailed microphysical column models through mesoscale up to the global scale, capable of modeling the Martian weather and climate including CO2 cloud microphysics. We propose with the MECCOM project to perform numerical modeling of the Martian CO2 clouds at all scales to answer the burning questions on the role of these clouds in the Martian climate. This is required for the full understanding of the current CO2 cycle on Mars, which is one of the major climatic cycles, and of the role of the clouds in the past, warmer climate, where liquid water may have flown on the surface. The constant flow of observations of the Martian atmosphere and the development of high-resolution models allow us now to start digging into the mesoscale phenomena of the Martian atmosphere that can play an important role in its global dynamics. The polar CO2 clouds are an example of such a phenomenon: their formation probably induces dynamics similar to moist convection on the Earth, influencing the polar vortex and larger scale dynamics of the atmosphere. The mesospheric clouds seem to be a result of interaction of planetary scale and mesoscale atmospheric waves and the availability of ice nuclei that possibly are provided by hydrated mesospheric ions, hypothesized only recently. This study draws also from a comparative planetology approach: latent heat-driven ("moist") convection, orographic waves and mesospheric clouds all are known phenomena also on the Earth. MECCOM project will allow the PI to build and consolidate a team, based at LATMOS, and surrounded by a strong, highly qualified national and international network of collaborators, which it will strengthen and in which it can evolve. MECCOM will also use and promote French supercomputing resources and European space mission data.

The Tropical Tropopause Layer (TTL) is the region of the atmosphere between 30S and 30N which is bounded by the convectively dominated tropical troposphere below and the layered motion in the stratosphere regulated by the Brewer Dobson circulation above. The TTL is the gateway which processes the air lofted from the surface by convection, including anthropogenic pollution, and controls the composition of the stratosphere. Due to this role and the radiative effects of its ubiquitous cirrus clouds, which are regulating the convection underneath, the TTL is a key component of the climate system. During summer, the TTL is mostly under the influence of the Asian monsoon where the upper layer circulation is dominated by a large anticyclone extending from east Asia to the Mediterranean sea. This circulation ventilates the convection and redistributes the lofted air. Since two decades, a new aerosol layer (ATAL=Asian Tropopause Aerosol Layer), recently discovered, has developed near 16 km altitude inside the monsoon anticyclone and is attributed to the growing anthropogenic emissions at the ground. The impact of the monsoon on the TTL and the stratosphere, the distribution of ground sources, the transport properties across the TTL and the processes related to aerosols and cirrus within the TTL, in particular the ATAL, are still poorly known due to a lack of available observations and limited modeling studies. However, a wealth of new observations is now being provided by a new generation of satellite instruments and a series of campaigns in Asia based on international collaboration. The EU funded StratoClim airborne campaign in 2017 will provide a large amount of unparalleled in situ observations within the Asian monsoon TTL and the ATAL. The overarching goal of our project is to understand how does climate change affect the features of the TTL (cirrus, radiative budget and composition of the air entering the stratosphere) during the Asian monsoon season and what is the feedback on the climate. The investigated questions in this proposal are (i) the description of high altitude clouds and of their injection of water and tracer compounds in the TTL, (ii) the processes from small to large scale which regulate transport, the distribution of cirrus and aerosol, (iii) the radiative impact of clouds, in particular the thin cirrus, and aerosols in the Monsoon region, (iv) the full exploitation of available data. An immediate urgent question is to understand the change in composition manifested by the ATAL, to determine its chemical and physical properties, to understand and monitor the sources and precursors and to determine its direct and indirect glaciation radiative forcing and the induced modulation of stratospheric composition. These questions will be answered by a coordinate set of tasks. Multi-satellite data will be analyzed to determine the properties of high altitude clouds and aerosols. The StratoClim campaign data will be exploited using Lagrangian modeling methods to link the measurements to the sources and the history of air parcels. We will a new set of observations by light weight innovative instruments flying under small balloons and ATAL impact will be monitored by the ground-based lidars of the NDACC network.Two complementary models with full representation of chemical and micro-physical processes will be used to reproduce the ATAL and compared with the campaign and satellite data. Climatologies of relevant ground sources and transport pathways will be established. Climate change projections will be estimated. Our project will be conducted by a team that gathers the highest expertise in atmospheric modeling, observation and data analysis and is already well trained to work together. Our project is a unique opportunity to make the best usage of the most recent observations and to produce major advances on a key issue in climate science.