[Live radio] Recherche académique : indépendance TotalE

22/03/2023 19:00

Climat : la fin des saisons ?

15/03/2023 19:00

34e Journées Scientifiques de l’Environnement (JSE)

14/03/2023 19:00

From plankton images to marine ecosystem functioning: a tale of high throughput imaging, machine learning, and copepod ecology

29/06/2021 11:00

Sakina-Dorothée Ayata présentera rapidement ses thèmes de recherches et la manière dont elle envisage son intégration au LOCEAN, avant de présenter plus en détail les travaux résumés ci-dessous.

Proglacial and subglacial aquifers: their evolution under climate change and the potential impacts in terms of resources and natural hazards, through the case of eastern Iceland

25/06/2021 12:00

L’évolution des glaciers sous l’influence du changement climatique est largement étudiée, tant en terme de bilan de masse que des effets sur l’hydrologie de surface.

Climate Modeling in the Age of Machine Learning

23/06/2021 15:00

Numerical simulations used for weather and climate predictions solve approximations of the governing laws of fluid motions on a grid.

Understand and use the estimation of soil organic carbon persistence by Rock-Eval® thermal analysis

25/03/2022 14:00

One of the most important solutions to climate change lies literally right under our feet. Soils store twice the amount of carbon that is found in atmosphere and vegetation combined. They act as a buffer between solid earth and atmosphere and exercise a major control on the atmospheric concentration of CO₂ through the release or sink of greenhouse gases.

Moreover, organic carbon in soils in the form of organic matter is essential to soil health and fertility, to nutrient availability and water quality. My work is centred around the most valuable tool at our disposal for understanding and predicting the evolution of this reservoir in the future: soil organic carbon (SOC) dynamics models. A missing key influencing the accuracy of SOC model projections and a major challenge in soil science is our ability to estimate the proportion of SOC that will remain unchanged over projection-relevant timescales.

This important amount of carbon that has been present in soils for centuries or millennia, and is therefore considered to be “stable”, can vary greatly from one location to another. The goal of my thesis project was to explore a new approach based on thermal analysis of SOC and machine learning, to characterise SOC, estimate the proportion of “stable” carbon in soil samples, and eventually use this information to improve the accuracy of SOC dynamics models.

In a second step, I focused on the Rock-Eval® thermal analysis technique in the heart of this approach to understand better the important information it offers, based on model laboratory experiments. The main results of my thesis consist, on the one hand, of a complete and validated operational approach improving the accuracy of SOC models with a clear and significant value for “climate-smart” soil management.

On the other hand, an experimental part offers new insights into the working principle, limitations and possibilities of the Rock-Eval® thermal analysis technique.

La couche limite des régimes d'alizés et la sensibilité climatique

18/03/2022 15:00

En français

La réponse des nuages des régimes d’alizés au réchauffement climatique reste incertaine. Elle soulève notamment la possibilité d’une sensibilité climatique élevée due à une diminution de la fraction nuageuse sous l’effet de l’interaction entre le mélange convectif, la turbulence, le rayonnement et l’environnement à grande échelle. La campagne EUREC4A (Elucidation du rôle du couplage nuage-circulation dans le climat) a apporté de nouvelles observations qui permettent de mieux comprendre la physique des régimes d’alizés, et d’apporter pour la première fois une contrainte sur la rétroaction des cumulus d’alizés basée sur les processus.

Nous montrerons d’abord comment les observations EUREC4A permettent d’approfondir la compréhension de la structure verticale caractéristique de la couche limite des alizés et des processus qui produisent cette structure. Elles amènent à revisiter certains aspects des modèles conceptuels et suggèrent un rôle plus actif des nuages dans le maintien de cette structure. Cette compréhension physique est ensuite appliquée à l’évaluation des rétroactions des cumulus d’alizés. Nous montrerons que les observations rendent peu plausibles les fortes rétroactions des cumulus d’alizés en réchauffement climatique.

English

The response of trade-wind clouds to warming remains uncertain, raising the specter of a large climate sensitivity. Decreases in cloud fraction are thought to relate to interplay among convective mixing, turbulence, radiation, and the large-scale environment. The EUREC4A (Elucidating the role of cloud-circulation coupling in climate) field campaign made extensive measurements that allow for deeper physical understanding and the first process-based constraint on the trade cumulus feedback, as described in this talk.

I first use EUREC4A observations to improve understanding of the characteristic vertical structure of the trade-wind boundary layer and the processes that produce this structure. This improved physical understanding  is then applied to the evaluation of trade cumulus feedbacks. Ideas developed support new conceptual models of the structure of the trade-wind boundary layer and a more active role of clouds in maintaining this structure, and show little evidence for a strong trade cumulus feedback to warming.

Modelling the oceanic Meridional Overturning Circulation: challenges and insights

10/03/2022 15:00

The objective of my habilitation is to review recent advances in the understanding of the meridional overturning circulation (MOC) and ocean modelling in parallel. Although the MOC is a complex oceanic structure, simple models provide useful insights into the processes that influence it. This is the method that I followed to clarify the role of eddies in convective basins where dense water is formed. More complex models, representing the whole ocean dynamics on a global scale, allow to examine the interactions between processes and the associated mechanisms of variability. I have then shown that the link between MOC and dense water formation depends on the spatial resolution of the ocean model, a critical parameter for the representation of western boundary currents. Unfortunately, the production of such models is costly and prevents the quantification of uncertainties related to numerical choices. For this reason, it is preferable to use climate models, which are less expensive because of their corser spatial resolution. I have therefore focused on IPSL-CM6 model since 2015 and conducted a collaborative project exploring various parameterizations and spatial resolutions, in the atmosphere and the ocean, to quantify the uncertainties of the simulations produced for CMIP6. The most important result is that the uncertainty related to model calibration is as large as that related to spatial resolution, for the range of resolutions explored (1/4 to 1 degree in the ocean). This motivates to develop new methods to calibrate ocean and climate model parameters, as well as to improve the parameterizations of fine scale processes in coarse resolution models, two objectives that are central in my future projects.