Pourquoi et comment initier une transition dans les laboratoires ?

15/02/2023 10:00

La mission Uvsq-Sat fête ses deux ans en orbite, 2 ans dédiés à la mesure du bilan radiatif de la Terre

20/01/2023 12:30

Hommage à Anny-Chantal Levasseur-Regourd

09/12/2022 09:00

Planning without appropriate data and model is gambling: Lake Urmia crisis and restoration plan

03/12/2021 12:00

Lake Urmia is the second-largest hyper-saline lake in the world. Lake Urmia’s water level has dropped drastically from 1277.85 m to 1270.08 m a.s.l (equal to 7.77 m) during the last 20 years, equivalent to a loss of 70% of the lake area.

Peut-on détecter un cyclone avec le modèle YOLO développé pour la conduite autonome ?

23/11/2021 14:00

La détection de cyclone est une tâche difficile. En effet, les cyclones sont des évènements dynamiques, i.e. leur forme et taille évoluent rapidement dans le temps. De plus, un manque de données annotées par des experts rend difficile l’entraînement d’un modèle de Machine Learning.

A quantitative scaling theory for meridional heat transport by baroclinic turbulence

22/11/2021 11:00

Séminaire hebdomadaire du LMD à l’ENS.

Caractérisation de la banquise Arctique à partir d'observations micro-ondes multi-instruments et multi-fréquences

16/11/2022 14:30

La glace de mer joue un rôle majeur dans la circulation océanique et dans le système climatique et météorologique. Dans un contexte de réchauffement climatique, où l’étendue de la glace de mer arctique diminue régulièrement depuis 40 ans, le suivi et la surveillance de l’Arctique sont essentiels. Les instruments micro-ondes embarqués sur les satellites permettent d’étudier cette région de la Terre par tous les temps, indépendamment du cycle jour/nuit. Particulièrement adaptées à l’observation des régions polaires où la présence de nuages est importante et où la nuit polaire dure six mois, les observations par satellite micro-ondes sont la pierre angulaire des estimations des paramètres géophysiques de la glace de mer.
Néanmoins, la compréhension de la physique sous-jacente aux signatures micro-ondes observées est encore partielle. Cette thèse vise à améliorer notre compréhension des signaux micro-ondes de la glace de mer.

Impact of the spatial and temporal variability of the Mistral on dense water formation in the Mediterranean Sea

21/10/2022 14:00

Deep convection is the process where surface water is cooled to the point it becomes dense enough that it sinks to the seafloor. In the Gulf of Lion, the dense water it produces helps the general circulation of the Mediterranean Sea. In this region, the cooling is mainly caused by the Mistral winds and seasonal change of the atmosphere. This thesis explores the individual and relative cooling provided by these two sources, finding that both sources contribute to the cooling, with the seasonal change providing more than the Mistral. However, in the future neither are able to overcome the predicted changes to the gulf due to climate change, and deep convection is believed to stop altogether. Due to this, part of the thesis looks at methanol producing islands; devices that could help mitigate climate change and energy availability, especially in the Mediterranean.

Local and remote sources of Arctic air pollution

09/09/2022 10:00

The Arctic region is warming faster than any other region on Earth due to the effect of greenhouse gases, notably CO₂, and short-lived climate forcers of anthropogenic origin, such as black carbon (BC). Over the last 20-30 years, remote anthropogenic emissions over mid-latitude regions have been decreasing. Anthropogenic emissions within the Arctic are also contributing and might increase in the future and further affect Arctic air pollution and climate. Natural emissions, such as sea-spray aerosols, also might increase due to on-going climate change. However, the processes and sources influencing Arctic aerosols and trace gases are poorly quantified, especially in wintertime.

In this thesis, quasi-hemispheric and regional simulations are performed using the Weather Research Forecast model, coupled with chemistry (WRF-Chem). The model is used to investigate atmospheric composition over the wider Arctic and during two field campaigns, one in northern Alaska at Barrow, Utqiaġvik in January and February 2014 and the second in Fairbanks, central Alaska in November and December 2019 during the French pre-ALPACA (Alaskan Layered Pollution And Chemical Analysis) campaign.

First, modelled inorganic and sea-spray (SSA) aerosols are evaluated at remote Arctic sites during wintertime. Then, the model is improved with respect to SSA treatments, following evaluation against Barrow field campaign data, and their contribution to the total aerosol burden within the Arctic region is quantified. A series of sensitivity runs are performed over northern Alaska, revealing model uncertainties in processes influencing SSA in the Arctic such as the presence of sea-ice and open leads. Second, a sensitivity analysis is performed to investigate processes and sources influencing wintertime BC over the wider Arctic and over northern Alaska, with a focus on removal treatments and regional emissions. Variations in model sensitivity to wet and dry deposition are found across the Arctic and could explain model biases. Over northern Alaska, regional emissions from petroleum extraction are found to make an important contribution to observed BC.

Model results are also sensitive to planetary boundary layer parameterisation schemes. Third, the improved version of the model is used to investigate the contribution of regional and local sources on air pollution in the Fairbanks area in winter 2019. Using up-to-date emissions, the model performs better in winter 2019 than in winter 2014, when compared to observations at background sites across Alaska. Underestimations in modelled BC and sulphate aerosols can be partly explained by lacking local and regional anthropogenic emissions. In the case of sulphate, additional secondary aerosol formation mechanisms under dark/cold conditions also need to be considered.