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Dynamics, predictability, impacts, and climate change considerations of the catastrophic Mediterranean Storm Daniel (2023)
No full textInternational audienceIn September 2023, storm Daniel formed in the centre of the Mediterranean Sea as an intense Mediterranean cyclone. Its formation was accompanied by significant socioeconomic impacts in Greece including several fatalities and severe damages to agricultural infrastructures. Within a few days, the cyclone evolved into a tropical-like storm, i.e., medicane, that made landfall in Libya, probably marking the most catastrophic and lethal weather event that was ever documented in the region. In this study, we place storm Daniel as the centrepiece of the catastrophic events in Greece and Libya. We thus consider that there is a direct link between the atmospheric processes that turned Daniel into a catastrophic storm and the actual socioeconomic impacts that a single weather system has produced in the two countries. We perform a holistic analysis that articulates between atmospheric dynamics, precipitation extremes, and quantification of impacts, i.e., floods and sea state. This is done by taking into account the predictability of Daniel at weather scales and the attribution of impacts to climate change.Our results show that Daniel initially formed like any other intense Mediterranean cyclone. At this stage, the cyclone produced significant socioeconomic impacts on Greece, in an area far from the cyclone centre. In later times, Daniel attained tropical-like characteristics while gradually reaching its maximum intensity. Impacts over Libya coincided with the cyclone's landfall at its maturity stage. The predictability of the cyclone formation was rather low even in relatively short lead times -of the order of four days-while higher prediction skill was found when addressing the landfall in Libya for the same lead times. Our analysis of impacts shows the adequate capacity of numerical weather forecasting to capture the extremeness of precipitation amounts and floodings in Greece and Libya.Therefore, state-of-the-art numerical weather prediction has provided information on the severity of the imminent flood events.We also analyse the moisture sources contributing to extreme precipitation. Results show that moisture sources were majorly driven by large-scale atmospheric circulation, while in maturity, Daniel drew substantial amounts of water vapor from local maritime areas within the Mediterranean Sea. In a climatological context, Daniel was indeed shown to produce extreme precipitation amounts, and our analysis allows us to interpret Daniel's impacts as an event whose characteristics can be ascribed to human-driven climate change</p
Enhanced short-duration precipitation and divergent rainfall spatial patterns of Typhoon Nida (2016) under the impact of urbanization
No full textInternational audienceTropical cyclones (TCs), when approaching coasts and after landfalling, may exhibit significant interactions with heavily urbanized surfaces. Despite numerous studies, the effects of urbanization on TCs and their landfalling processes remain insufficiently explored. Typhoon Nida, landfalling in the Pearl River Delta region on August 1, 2016, provides an interesting case for us to revisit the issue. We use the Weather Research and Forecasting model in paired numerical experiments to isolate the urban effects. Urban land cover has a small impact on the track and the intensity of the typhoon. Urban effect on landfalling precipitation in this event is mainly profound in changing rainfall spatial patterns rather than the average rain rate. The accumulated precipitation and the rain rate of the major urban area are reduced. During different stages of the TC rapid movement, enhanced precipitation is observed at the downwind and upwind regions within a short duration. The increase in surface temperature and sensible heat flux enhances thermal circulation; however, this effect is weakened under the strong synoptic background during landfall. Increasing urban surface roughness decelerates airflows and enhances updrafts along the urban boundaries, producing enhanced water vapor convergence and bifurcated winds, increasing downwind precipitation with a maximum value of 46.17 mm in 6 h. Throughout the TC rapid movement, urban modification on precipitation patterns displays high spatial variability over short periods. The study raises concern about more extreme hazards occurring in multiple locations over urban areas caused by urban-induced TC rainfall redistribution
Temporal variability of spectral Granger causality from electroencephalograms during sleep: a time-frequency approach
No full textEmerging Climate Signals in Oxygen Minimum Zones
No full textAbstract. The ocean is losing oxygen due to anthropogenic climate change. This loss is particularly worrying when it occurs in naturally low-oxygen regions, such as the Oxygen Minimum Zones (OMZs) found at mid-depth in tropical oceans, because the expansion of OMZs reduces habitable space for marine life and threatens oxygen-dependent ecosystems. However, detecting the emergence of climate-driven signals is challenging due to internal variability. Here, we isolate externally forced signals of OMZ volume change and regional deoxygenation, and determine their time of emergence using the IPSL-CM6A-LR Large Ensemble. We apply time of emergence analysis to identify when climate-driven signals become statistically distinguishable from natural variability. Our results show that OMZ edges consistently expand, with emergence occurring in the second half of the 20th century, which is in phase with regional mean deoxygenation in the tropical Pacific and tropical Atlantic. In contrast, we reveal a marked spatial asymmetry in the emergence of OMZ core and hypoxic volumes between the northern and southern parts of OMZs. While OMZ core volumes in the tropical North Pacific and hypoxic volumes in the tropical North Atlantic expand, their southern counterparts contract due to a sudden, ventilation-driven oxygen increase from the Southern Ocean at the start of the 21st century. Uncertainties in emergence timing range from 20 to 30 years across ensemble members, and increase substantially in regions influenced by abrupt changes in OMZ ventilation. By linking the emergence of regional deoxygenation to that of OMZ volume changes, climate-driven expansions of OMZ volumes are likely already beginning to emerge, with distinct dynamics between northern and southern tropical oceans
Dual communication in a social network: Contributing and dedicating attention
No full textInternational audienceCommunication between individuals often involves two types of dual activities. On social media such as Facebook, for example, users produce content (posts) and pay attention to their friends' posts. These activities are dual as a user is more inclined to produce posts the more friends react to them and is more inclined to dedicate attention to a friend's posts the more numerous these posts are. This paper builds and analyzes a simple game with dual activities and dedicated attention when agents communicate through a follower-influencer network (say, X-Twitter). Equilibria can be multiple, each characterized by its attention network, which describes who pays attention to whom, resulting in a partition of cohesive subgroups who pay and receive attention from each other and do not communicate with agents in other subgroups. The stars-equilibria, where attention in each subgroup is focused on a single influencer, stand apart: activities and payoffs are high on average but unequal. Furthermore, they are the only equilibria stable to perturbations or to self-enforcing deviations from coalitions (coalition-proofness)
Global Carbon Budget 2025
No full textAccurate assessment of anthropogenic carbon dioxide (CO2) emissions and their redistribution among the atmosphere, ocean, and terrestrial biosphere in a changing climate is critical to better understand the global carbon cycle, support the development of climate policies, and project future climate change. Here we describe and synthesise datasets and methodologies to quantify the five major components of the global carbon budget and their uncertainties. Fossil CO2 emissions (EFOS) are based on energy statistics and cement production data. Emissions from land-use change (ELUC) are estimated by bookkeeping models based on land-use and land-use change data. Atmospheric CO2 concentration is measured at surface stations, and the global atmospheric CO2 growth rate (GATM) is computed from the annual changes in concentration. The global net uptake of CO2 by the ocean (SOCEAN, called the ocean sink) is estimated with global ocean biogeochemistry models and observation-based fCO2products. The global net uptake of CO2 by the land (SLAND, called the land sink) is estimated with dynamic global vegetation models. Additional lines of evidence on land and ocean sinks are provided by atmospheric inversions, atmospheric oxygen measurements, ocean interior observation-based estimates, and Earth System Models. The sum of all sources and sinks results in the carbon budget imbalance (BIM), a measure of imperfect data and incomplete understanding of the contemporary of 2023-2024 in the Northern Hemisphere. The ocean CO2 sink was 3.2 ± 0.4 GtC yr -1 during</div
Plant-Level Productivity in a Declining Market: The Case of Union Locals
No full textInternational audienc
The diurnal cycle and temperature dependence of crystal shapes in ice clouds from satellite lidar polarized measurements
No full textInternational audienceAbstract. The shape of crystals in ice clouds influences many aspects of the cloud lifecycle and radiative impact, yet they are extremely variable and hard to categorize. In this paper, we apply a recent crystal shape classification methodology to 33 months of spaceborne lidar measurements. We take advantage of their non-sun-synchronous nature to document the diurnal variability of ice crystal shapes. We find that that mid-level clouds are dominated by 3D bullets and 2D columns, with more 3D bullets at higher latitudes, in agreement with previous results. Shape dependence on latitude is generally symmetric around the equator. We document the repartition of shapes with temperatures, and show that the proportion of complex shapes (Droxtals and Voronois) increases at colder temperatures, becoming dominant below -60 °C. Finally, we document the diurnal cycle of the repartition of shapes according to temperature and latitude. We find that 2D plates and columns appear preferentially during daytime, while complex shapes are more likely to appear during nighttime. 3D bullets follow a unique behavior, shifting from a daytime maximum at coldest temperatures to a nighttime maximum at warmer temperatures. The amplitude of diurnal cycles generally strengthens at colder temperatures. These results provide new constraints for the representation of ice clouds in atmospheric and climate models
Intermediate-complexity parameterisation of blowing snow in the ICOLMDZ AGCM: development and first applications in Antarctica
No full textInternational audienceRecent regional model findings suggest that the aeolian erosion of surface snow is a significant contribution to the overall Antarctic surface mass balance (SMB) through ice crystals sublimation and export outside of the ice sheet. Such findings raise the question of the relevance of accounting for such a process also in global climate models. This study presents the development of an intermediate-complexity parameterisation of blowing snow for the ICOLMDZ atmospheric general circulation model, the atmospheric component of the IPSL Coupled Model. The parameterisation is designed to be a trade-off between physical complexity and applicability in a general circulation model, with constrains on numerical cost and stability. The parameterisation is evaluated with in situ observations using limited-area simulations over Adélie Land. The model exhibits satisfactory results in terms of summer wind speed, temperature and intensity of blowing snow fluxes. In winter, blowing snow intensity and occurrences are overestimated close to the coast, concurring with a positive wind speed bias. In terms of blowing snow occurrences throughout the year, ICOLMDZ exhibits comparable performance with the regional atmospheric model MAR. Boundary-layer moistening and cooling as well as changes in surface radiative fluxes due to blowing snow crystals are also quantified in the simulations. Global simulations at standard global climate model resolution are carried out to investigate how the Antarctic surface mass balance is modified with the activation of the blowing snow parameterisation. Results show an overall decrease of the net snow accumulation in the escarpment region due to surface snow erosion and an increase along the coast due to blowing snow deposition and increase in precipitation
Optimisation stochastique pour la conception et la gestion de chaînes d'approvisionnement en hydrogène
No full textHydrogen plays a central role in the transition to decarbonizedenergy systems, but designing and operating its supply chain raises complex,interdependent decisions under uncertainty. This thesis applies(stochastic) optimization techniques to the design andmanagement of hydrogen infrastructures.Two realistic case studies are treated; the first case study concerns amono-site hydrogen infrastructure which consists of an electrolyzer, acompressor and a storage to serve a transportation demand. This infrastructureis powered by three sources of energy (on site photovoltaics, renewableelectricity through power purchase agreement, power grid) with their owncharacteristics. The modelling of the electrolyser covers its differentfunctioning modes and the nonlinear relation between the production of hydrogenand the electricity consumption. The optimization problem is to minimize theoperational costs over a week (while emphasizing the use of renewable sources),by making hourly decisions in the presence of uncertainties. Indeed, we consider uncertaintiesaffecting on site photovoltaics production and hydrogen demand. We formulate amultistage stochastic optimization problem, and we develop suitablealgorithms based on Lagrange decomposition and Dynamic Programming. Moreover, westudy the design of such infrastructure, which leads to the study of a specialclass of minimax optimization problems.The second case study focuses on a deterministic hydrogen transport problemwhere mobile storage units themselves are moved by trucks between supply anddelivery locations to meet mobility demands, involving swap operations uponarrival. This contrasts with existing literature where inventories remainstationary. The objective is to optimize daily routing and refilling schedulesof the mobile storages. We model the transport problem as a flow problem on atime-expanded graph, and we propose an equivalent Mixed Integer Linear Programming(MILP) formulation, which can be efficiently solved with standard MILP solversfor medium-sized instances. For large instances of the problem, we use atwo-step heuristic.L’hydrogène joue un rôle central dans la transition vers des systèmes énergétiques décarbonés, mais la conception et l’exploitation de sa chaîne d’approvisionnement soulèvent des décisions complexes et interdépendantes sous incertitude. Cette thèse applique des techniques d’optimisation (stochastique) à la conception et à la gestion des infrastructures d’hydrogène. Deux études de cas réalistes sont traitées ; la première concerne une infrastructure d’hydrogène mono-site composée d’un électrolyseur, d’un compresseur et d’un stockage pour répondre à une demande de transport. Cette infrastructure est alimentée par trois sources d’énergie (photovoltaïque sur site, électricité renouvelable via contrat d’achat d’électricité, réseau électrique) ayant chacune leurs propres caractéristiques. La modélisation de l’électrolyseur couvre ses différents modes de fonctionnement et la relation non linéaire entre la production d’hydrogène et la consommation d’électricité. Le problème d’optimisation vise à minimiser les coûts d’exploitation sur une semaine (tout en favorisant l’utilisation des sources renouvelables), en prenant des décisions horaires en présence d’incertitudes. Nous considérons en effet des incertitudes affectant la production photovoltaïque sur site et la demande d’hydrogène. Nous formulons un problème d’optimisation stochastique multistade, et développons des algorithmes adaptés basés sur la décomposition de Lagrange et la Programmation Dynamique. De plus, nous étudions la conception d’une telle infrastructure, ce qui conduit à l’étude d’une classe particulière de problèmes d’optimisation minimax. La deuxième étude de cas se concentre sur un problème déterministe de transport d’hydrogène où des unités de stockage mobiles sont elles-mêmes déplacées par des camions entre des sites d’approvisionnement et de livraison pour répondre à des demandes de mobilité, impliquant des opérations d’échange à l’arrivée. Cela contraste avec la littérature existante où les inventaires restent stationnaires. L’objectif est d’optimiser les itinéraires quotidiens et les plannings de remplissage des stockages mobiles. Nous modélisons ce problème de transport comme un problème de flot sur un graphe étendu dans le temps, et proposons une formulation équivalente en Programmation Linéaire en Nombres Entiers Mixtes (MILP), qui peut être résolue efficacement avec des solveurs MILP standards pour des instances de taille moyenne. Pour les grandes instances du problème, nous utilisons une heuristique en deux étapes