L’engagement des scientifiques en débats

21/05/2024 13:00

Lunes glacées et mondes océans autour de Jupiter et Saturne

14/05/2024 14:30

En cas de doute, foncez !

26/04/2024 18:30

Webinaire formats de stockage pour le Deep Learning en Python

24/05/2023 11:00

Le groupe ESPRI-IA qui a pour but de promouvoir l’entraide technique et méthodologique sur l’IA, a le plaisir de vous annoncer son troisième séminaire sur une étude des formats de stockage Python (Numpy, HDF5 et Zarr) et des codecs de compression (lz4, zstd, blosc, etc.) pour la gestion de grands datasets d’entraînement en Deep Learning.

Découvrez ClimarisQ : le jeu smartphone/web qui vous engage dans la lutte pour le climat

23/05/2023 11:00

Vous êtes un.e scientifique passionné.e par les enjeux environnementaux et le changement climatique ? Vous cherchez un moyen amusant et éducatif d’approfondir vos connaissances sur le système climatique ? Ne cherchez plus ! Nous vous invitons à découvrir ClimarisQ, un jeu passionnant conçu pour sensibiliser les joueur.euses aux impacts du changement climatique et à l’urgence d’une action.

Séminaire de présentation du Centre de Calcul et de Données ESPRI de l'IPSL

22/05/2023 14:00

Les équipes du centre de calcul et de données ESPRI de l’IPSL vous invitent à un séminaire pour vous présenter les services que nous opérons et qui peuvent être utiles pour vos projets : mise à disposition de moyens de calcul intensif distribué, accès à des bases de données diverses, espace de stockage, plateformes de diffusion de données scientifiques, hébergement de projets.

Ice nucleating particles from natural sources and the modelling of their interactions with Arctic clouds

08/12/2025 09:30

[français]
Les noyaux glaçogènes (INP, pour Ice Nucleating Particles) sont des particules d’aérosols capables de favoriser la formation de cristaux de glace dans les nuages. En Arctique – où le réchauffement climatique est environ quatre fois plus rapide que la moyenne globale – les nuages contenant de la glace dominent l’atmosphère. En particulier, les nuages en phase mixte (c’est-à-dire composés à la fois de phases liquide et solide) y sont fréquents. Dans la modélisation du climat arctique, les erreurs liées à la représentation de la répartition des phases nuageuses affectent fortement la précision des modèles, car la phase nuageuse influence le bilan radiatif, les précipitations et la durée de vie des nuages. Ces propriétés dépendent des interactions aerosol-nuage, dont la représentation dans les modèles demeure limitée par la connaissance encore restreinte – bien qu’en progression – des INP. Les principales questions ouvertes concernent l’identification des espèces d’INP pertinentes en Arctique, leurs sources, leur efficacité à initier la glace ainsi que leur influence sur les nuages et le bilan radiatif. Autant d’inconnues qui persistent à freiner l’amélioration de la modélisation du climat arctique.

Dans cette thèse, j’aborde le rôle des INP dans les interactions aérosol-nuage en Arctique et leur impact sur les propriétés nuageuses, en trois étapes. Premièrement, je développe, évalue et applique une nouvelle méthodologie d’identification des sources d’émission d’INP, fondée sur le modèle lagrangien FLEXPART-WRF et combinée à des données d’observation. J’utilise ensuite cette méthode pour mieux comprendre les origines et les espèces contribuant aux concentrations d’INP récemment mesurées. Deuxièmement, j’introduis dans le modèle régional WRF-Chem de nouvelles sources d’aérosols aux hautes latitudes, que j’associe à des paramétrisations de nucléation de la glace afin de représenter la dynamique des populations d’INP en Arctique. Enfin, après comparaison des INP simulés avec les observations, je les couple au schéma de microphysique sensible aux aérosols de WRF-Chem, afin d’étudier leur effet sur les nuages arctiques durant l’été, période où l’occurrence des nuages en phase mixte et les concentrations d’INP sont les plus élevées.

Les résultats montrent que, dans l’Arctique central, les INP proviennent principalement de sources continentales ou marines situées près des côtes russes des mers de Barents et de Laptev, ainsi que des côtes du Groenland, sources connues d’émissions de poussières minérales. De plus, certains résultats suggèrent des sources biologiques issues de l’océan Arctique dépourvu de banquise pour les INP actifs à des températures supérieures à −15 ◦ C. L’intégration de ces émissions de hautes latitudes, combinée aux paramétrisations adéquates de nucléation de la glace, a permis une représentation réaliste des concentrations d’INP arctiques dans WRF-Chem. Lorsque la dépendance à la température est prise en compte pour l’activation, la fraction activée des INP simulés diminue de plusieurs ordres de grandeur par
rapport à celle obtenue avec des paramétrisations qui ne dépendent que de la température. Cela entraîne des effets significatifs sur la microphysique des nuages, en particulier dans l’Arctique central, soulignant la potentielle forte influence des INP, ainsi que la nécessité de développer des schémas de microphysique plus adaptés à la sensibilité des nuages aux aérosols.

 

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[english abstract]
Ice nucleating particles (INPs) are aerosol particles capable of promoting the formation of ice crystals in clouds. In the Arctic–where global warming occurs about four times faster than the global average–clouds containing ice dominate the atmosphere. In particular, mixed-phase clouds (i.e. clouds composed of both liquid and solid phases) are common. When modelling the Arctic climate, errors in the representation of cloud phase partitioning strongly affect model accuracy, as cloud phase influences the radiative budget, precipitation, and cloud lifetime. All these properties depend on aerosol-cloud interactions, whose representation in models remains limited by the still scarce- although growing–knowledge of INPs. Key open questions include identifying the relevant INP species in the Arctic, their sources, their efficiency in ice nucleation, and ultimately their influence on clouds and the radiative budget–questions that continue to hinder improvements in Arctic climate modelling.

In this thesis, I address in three steps the role of INPs in Arctic aerosol-cloud interactions and their impact on cloud properties. First, I develop, evaluate, and apply a new methodology for the identification of INP emission sources, based on the Lagrangian model FLEXPART-WRF combined with observational data. I then use this method to shed new light on the origins and species contributing to recently measured INP concentrations. Second, I implement new high-latitude aerosol sources in the regional model WRF-Chem, and use them together with ice-nucleation parameterisations to represent the dynamics of INP populations in the Arctic. Finally, after comparing the modelled INPs with observations, I couple them to the aerosol-aware microphysics scheme of WRF-Chem in order to investigate their effect on Arctic clouds during summer, when mixed-phase cloud occurence and INP concentrations are the highest.

Results show that, in the central Arctic, INPs mainly originate from continental or marine sources near the
Russian coasts of the Barents and Laptev Seas, as well as from coastal Greenland, where mineral dust emissions are known to occur. In addition, some results suggest biological sources from the ice-free arctic ocean for INPs active at temperatures above −15 ◦ C. The implementation of these high-latitude emissions, together with corresponding ice-nucleation parameterisations, enabled a realistic representation of Arctic INPs in WRF-Chem. When temperature-dependent activation was applied, the activated fraction of modelled INPs dropped by several orders of magnitude compared to those produced by purely temperature-based parameterisations. This had significant impacts on cloud microphysics, especially in the central Arctic, highlighting a potentially strong influence of INPs, and the need for updated aerosol-aware microphysics schemes.

Modelling and assessing agrivoltaics as a solution to the climate-water-energy-food nexus in the context of climate change in the Euro-Mediterranean region

27/11/2025 14:00

Climate change in the Euro-Mediterranean (EUROMED) region exacerbates agricultural challenges by increasing land vulnerability and reducing water availability. In response to these pressures, agrivoltaics (AVs), which combines photovoltaic (PV) energy production with agriculture on the same land, offers a promising solution within the water-energy-food-ecosystem (WEFE) nexus. AVs can enhance agricultural resilience, reduce water consumption, promote renewable energy and reduce land-use conflicts. By creating partial shading, AVs alleviates thermal stress and limits soil water evaporation, enhancing crop microclimate. However, AV performance is highly dependent on climate, crop type, and geographical context, requiring modeling tools capable of assessing AV performance at regional scales. Yet, current literature mostly focuses on site-specific models, lacking a broader, holistic approach. To address this gap, we develop a novel regional-scale AV modeling framework by integrating a PV module with the ORCHIDEE (Organizing Carbon and Hydrology In Dynamic Ecosystems) land surface model. The AV model modifies solar radiation and wind speed from regional climate models, which -along with other meteorological inputs- are fed into ORCHIDEE to simulate energy, water, carbon and nitrogen fluxes at the land surface. By prescribing agricultural soil parameters, this integrated approach enables to explore AV impacts within the WEFE nexus under both current and future climate conditions. In the first part of this project, we apply the AV model using reanalysis climate data to assess AV performance under current climate conditions in two contrasting regions: the Iberian Peninsula and the Netherlands. In the drier Iberian Peninsula, AVs offers substantial benefits, particularly under drought conditions. These include improved yields, food security, and water and land use efficiency, alongside clean energy production. Simulations with varying nitrogen fertilizer levels indicate that AVs can enhance nitrogen use efficiency and maintain or increase productivity of conventional systems, while reducing green house gas emissions. In contrast, in the Netherlands -where precipitation is more abundant and solar radiation is lower- AVs tends to reduce crop yields, with limited resource efficiency gains. This contrast suggests an heterogeneous potential for AV deployment in the EUROMED region, which spans arid to temperate zones. To further explore this, the second part of the study applies the model to the entire EUROMED basin using EURO-CORDEX climate projections under RCP 8.5. This enables an evaluation of AV systems as a climate adaptation strategy within the WEFE nexus. Results show that AV benefits are strongly influenced by regional climate trajectories and water availability trends. Southern, drought-prone areas are especially well-suited for AVs, with high potential to reduce water stress and sustain agricultural productivity under warming conditions. In northern, wetter regions, the benefits are less evident, emphasizing the need for targeted deployment.

Drivers of low‑level cloud seasonality over sea ice and Greenland: Insights from 13 years of spaceborne lidar observations,

20/10/2025 09:30

Arctic clouds play a critical role on the sea-ice and Greenland Ice-sheet by modulating the energy received at the surface. The surface cloud radiative effect (CRE) results from two competitive effects: a shortwave cooling effect, the umbrella effect, and a longwave warming effect, the blanket effect. When considering both the Greenland ice-sheet and the sea-ice, the CRE is dominated by the longwave component and lead to a net warming effect at the surface, except for a short period in summer. As a result, they may limit sea-ice growth during winter, trigger melt events in spring or delay the freeze-up of both sea-ice and the Greenland Ice-sheet during fall. This thesis investigates the drivers of low-level clouds seasonality over the sea-ice and the GrIS, which remain poorly understood, and the associated effect on the surface radiative budget, using 13 years of space-based active cloud remote sensing by CALIPSO.

We distill three key results that clarify the seasonal controls on Arctic low-level clouds and their surface radiative impact:

(i) The steep spatially homogeneous increase of low-level optically thick clouds over the sea-ice in spring was attributed to the increase of lower troposphere temperature. While moisture transport from mid-latitudes is already sufficient to trigger the transition earlier in spring, the steep transition of temperature, from ∼−20°C in March to ∼−13oC in May, favors the formation of more liquid-containing clouds (optically thick) against ice clouds (optically thin).

(ii) From winter to spring, we reveal a weak but statistically significant control of surface pressure on the radiative effect of clouds over the Arctic sea-ice. This weak control is likely to explain the regional patterns of surface cloud radiative warming for a given period: minimum in April over the Beaufort Sea and maximum in winter-early spring over the Barents Sea.

(iii) Using a machine learning approach, we demonstrate that the surface cloud radiative warming increase of +10W/m² in September compared to July over the Greenland west coast is attributed to frequent « polar low » circulation in the Baffin Sea, advecting clouds over the coast. This maximum occurs still in a period considered as the melt season, over a region representing 22% of the total mass loss of the ice-sheet over the last two decades.

These results suggest that space-based active cloud observations over the sea-ice and the GrIS provide strong observation constraints, helping to overcome past limitations due to the scarcity of Arctic cloud measurements. Future studies should exploit new missions such as EarthCARE to better understand the drivers of Arctic cloud seasonality and radiative effects in summer for instance.