Influence of El Niño on the variability of global shoreline position

Coastal zones are fragile and complex dynamical systems that are increasingly under threat from the combined effects of anthropogenic pressure and climate change. Using global satellite derived shoreline positions from 1993 to 2019 and a variety of reanalysis products, here we show that shorelines are under the influence of three main drivers: sea-level, ocean waves and river discharge. While sea level directly affects coastal mobility, waves affect both erosion/accretion and total water levels, and rivers affect coastal sediment budgets and salinity-induced water levels. By deriving a conceptual global model that accounts for the influence of dominant modes of climate variability on these drivers, we show that interannual shoreline changes are largely driven by different ENSO regimes and their complex inter-basin teleconnections. Our results provide a new framework for understanding and predicting climate-induced coastal hazards

Coastal Wave Extremes around the Pacific and Their Remote Seasonal Connection to Climate Modes

At first order, wind-generated ocean surface waves represent the dominant forcing of open-coast morpho-dynamics and associated vulnerability over a wide range of time scales. It is therefore paramount to improve our understanding of the regional coastal wave variability, particularly the occurrence of extremes, and to evaluate how they are connected to large-scale atmospheric regimes. Here, we propose a new “2-ways wave tracking algorithm” to evaluate and quantify the open-ocean origins and associated atmospheric forcing patterns of coastal wave extremes all around the Pacific basin for the 1979–2020 period. Interestingly, the results showed that while extreme coastal events tend to originate mostly from their closest wind-forcing regime, the combined influence from all other remote atmospheric drivers is similar (55% local vs. 45% remote) with, in particular, ~22% coming from waves generated remotely in the opposite hemisphere. We found a strong interconnection between the tropical and extratropical regions with around 30% of coastal extremes in the tropics originating at higher latitudes and vice-versa. This occurs mostly in the boreal summer through the increased seasonal activity of the southern jet-stream and the northern tropical cyclone basins. At interannual timescales, we evidenced alternatingly increased coastal wave extremes between the western and eastern Pacific that emerge from the distinct seasonal influence of ENSO in the Northern and SAM in the Southern Hemisphere on their respective paired wind-wave regimes. Together these results pave the way for a better understanding of the climate connection to wave extremes, which represents the preliminary step toward better regional projections and forecasts of coastal waves

Modes de variabilité climatique dans l'océan Pacifique tropical : quantification des non-linéarités et rôle sur les changements de régimes climatiques

ENSO is the dominant mode of climate variability in the Pacific, having widespread socio-economical impacts. ENSO characteristics have been observed to exhibit substantial irregular variability from decadal to millennial timescales. The origin of such richness in ENSO variability timescales is likely due to the combined effects of timescales interaction processes within the tropical Pacific (through self-sustained nonlinear dynamics) and to external forcing (e.g. volcanic activity, changes in greenhouse gases...). In this thesis, we propose a new statistical framework that allows documenting high statistical moments in observed and simulated timeseries and that provides a robust estimation of nonlinearity in the tropical coupled system. As a first step, from the analysis of long-term CGCM simulations and extended reconstructed SST data sets, it is demonstrated that an interaction between interdecadal mean state changes in the tropical Pacific and extreme El Niño events probability occurs. This supports the hypothesis of ENSO variability being rectified at a wide range of frequencies by the slowly varying mean state through nonlinear processes phase-locked to the seasonal cycle alternatively in the Western and Eastern tropical Pacific. We then question to which extent the increase in greenhouse gases can alter the ENSO properties with a focus on its nonlinear character. Taking advantage of the IPCC database and different projections scenarios, nonlinearities are diagnosed in a model ensemble; and a relevant metric of the change in nonlinearity due to climate change is defined. This new metric allows highlighting a zonal see-saw in nonlinearity patterns associated with the change in El Niño characteristics observed in recent years. The traditional 20th century El Niño fingerprint, localized in the Cold Tongue, is robustly displaced westward in a warmer climate leading to El Niño Modoki-type patterns. We relate this switch in El Niño types to a change in nonlinearity pattern from present-day climate to a warmer climate. Secondly, we focused on the eastern tropical Pacific and the Humboldt Current System modelling and especially on the ability of Galapagos Islands and intra-seasonal activity in rectifying their mean state. Unlike recent studies, we put into perspective the role of this archipelago in altering this regional mean state. On the other hand, the intra seasonal Kelvin waves activity has the potential to revitalize the local mean circulation, the vertical stratification and therefore the Eastern Pacific dynamics, which in turn may have the potential to affect ENSO through upscaling effects.Dans cette thèse, nous nous sommes consacrés au problème d'interaction d'échelles selon deux angles distincts : d'une part une approche globale et grande échelle du système climatique qui nous a permis d'étudier la modulation basse fréquence d'ENSO, d'autre part une démarche plus locale au cours de laquelle nous avons étudié plus particulièrement la dynamique du Pacifique tropical est et du système de courants de Humboldt au large du Pérou. La première partie a été motivée par une approche relativement récente dans la communauté des climatologues. Il s'agit de la question cruciale de la variabilité basse fréquence d'ENSO, et de la possibilité que celle-ci puisse émerger " simplement " du système climatique tropical, sans action extérieure qu'elle soit stochastique ou en lien avec la variabilité des plus hautes latitudesDans ce contexte particulier, il est alors question de mécanismes nonlinéaires pour expliquer comment la stabilité d'ENSO peut être influencée par la variabilité climatique. Ceci a servi d'hypothèse de travail pour l'ensemble de cette thèse. Nous avons ainsi abordé la possibilité qu'ENSO pouvait être rectifié sur des échelles de temps longues (interdécennales) par la modulation de la nonlinéarité elle-même. Pour cela, nous avons utilisé des méthodes mathématiques originales qui nous ont permis d'une part de détecter des changements brusques (statistiquement significatifs) de l'état moyen du Pacifique tropical et d'autre part d'accéder à un proxy de la nonlinéarité intégrée dans le système tropical. En combinant ces deux démarches, nous avons pu mettre en évidence une boucle de rétroaction auto entretenue sur des échelles de temps longues qui serait pilotée par des mécanismes nonlinéaires qui auraient la capacité de faire interférer diverses échelles temporelles et ainsi de transférer l'énergie des basses fréquences (état moyen du pacifique tropical) vers les hautes fréquences (oscillation australe) et vice-versa. Dans la seconde partie de cette thèse nous nous sommes focalisés sur la modélisation climatique du Pacifique tropical oriental. En effet, cette région, pourtant au cœur des préoccupations de la communauté scientifique en raison de son écosystème parmi les plus productifs de la planète, reste mal connue du point de vue des processus océanographiques et climatiques. En particulier, les modèles climatiques globaux présentent des biais importants dans cette région en terme d'état climatologique moyen. Nous avons testé, dans une approche de modélisation haute résolution, différentes sources possibles de ces biais : les caractéristiques bathymétriques des îles Galápagos (mal représentées dans les modèles globaux) capables de par leur position équatoriale de modifier la circulation régionale moyenne et donc le bilan thermodynamique; ou alors les processus associés aux mélanges turbulents (et par extension les processus nonlinéaires) à l'aide d'un modèle régional. Pour ce faire, nous avons procédé à des expériences de sensibilité qui nous ont permis d'une part de relativiser le rôle de l'archipel des Galápagos comme source de biais et d'autre part de mettre en exergue le rôle de la variabilité intra-saisonnière dans la rectification de l'état moyen du Pacifique tropical est

Conception des lois de commande optimales pour l'amélioration de l'efficacité globale d'une chaîne de traction automobile

L'objectif premier des travaux thèse est de réduire la consommation d'essence d un véhicule hybride parallèle en réponse à une requête du conducteur. Après modélisation des transferts énergétiques au sein du véhicule, des algorithmes de contrôle locaux ont été développés pour déterminer le rapport de boîte et la répartition optimale de couple entre les motorisations en minimisant un critère incluant les aspects de consommation et d'agrément de conduite. Un second point consiste à déterminer les comportements optimaux d'un véhicule sur un trajet connu a priori. Une optimisation globale permettant de déterminer la consommation minimale a été développée. L'analyse des résultats permet alors, avec un système de navigation, d améliorer les algorithmes locaux pour mieux gérer les changements de rapport et le niveau de charge de la batterie. Pour valider cette approche, des tests de prototypage rapide et des test sur véhicule ont été réalisés.The main aim of the study is to determine the minimal fuel consumption of a parallel hybrid vehicle that fulfill the driver's request. First, a model representing the energy flows inside the vehicle was set. Then local control algorithms were developed to determine the optimal gear ratio and torque repartition between the motors by minimizing a criterion including consumption and driveability aspects. A second point of the thesis consists in extracting the optimal behavior of the car on a planned trip. A global optimization that computes the minimal consumption on the planned trip was developed. Considering a vehicle with a navigation system, the analysis of the results allows to improve the gear ratio and the battery charging management of the local algorithms. Fast prototyping tests and vehicle tests were made to validate this approach.TOULOUSE-ENSEEIHT (315552331) / SudocSudocFranceF

Direct and Rectified Effects of Tropical Instability Waves on the Eastern Tropical Pacific Mean State in a Regional Ocean Model

International audienceTropical instability waves (TIWs) are oceanic features propagating westward along the northern front of the Pacific cold tongue. Observational and modeling studies suggest that TIWs may have a large impact on the eastern tropical Pacific background state from seasonal to interannual time scales through heat advection and mixing. However, observations are coarse or limited to surface data, and modeling studies are often based on the comparison of low- versus high-resolution simulations. In this study, we perform a set of regional high-resolution ocean simulations (CROCO 1/12°) in which we strongly damp (NOTIWs-RUN) or not (TIWs-RUN) TIW propagation, by nudging meridional current velocities in the TIW region toward their monthly climatological values. This approach, while effectively removing TIW mesoscale activity, does not alter the model internal physics in particular related to the equatorial Kelvin wave dynamics. The impact of TIWs on the oceanic mean state is then assessed by comparing the two simulations. While the well-known direct effect of TIW heat advection is to weaken the meridional temperature gradient by warming up the cold tongue (0.34°C month−1), the rectified effect of TIWs onto the mean state attenuates this direct effect by cooling down the cold tongue (−0.10°C month−1). This rectified effect occurs through the TIW-induced deepening and weakening of the Equatorial Undercurrent, which subsequently modulates the mean zonal advection and counterbalances the TIWs' direct effect. This approach allows quantifying the rectified effect of TIWs without degrading the model horizontal resolution and may lead to a better characterization of the eastern tropical Pacific mean state and to the development of TIW parameterizations in Earth system models. Significance Statement Tropical instability waves (TIWs), meandering features at the surface of the equatorial Pacific Ocean, have long been recognized as a key component of the climate system that can even impact marine ecosystems. Yet, they are still hardly simulated in coupled global climate models. Here, we introduce a new framework to isolate and quantify their complex influence on the tropical Pacific background climate. This approach allows revealing a so far overlooked effect of TIWs on the mean circulation and heat transport in this region that should be accounted for in the next generation of global coupled climate models through parameterization or increased resolution

La vie culturelle juive en France après la Seconde Guerre mondiale (le "Colloque des intellectuels juifs de langue française" (1957-2000))

Au lendemain de la Seconde Guerre mondiale, la France fut le théâtre d un renouveau culturel aux développements inédits en Europe. Après la Shoah, des intellectuels juifs cherchèrent à redéfinir leur appartenance au judaïsme en développant un mouvement de pensée original, connu sous le nom d Ecole de pensée juive de Paris. Avec l école d Orsay, le Colloque des intellectuels juifs de langue française en fut le prolongement. Ses animateurs discutaient les thèmes liés à l actualité à la lumière des sources juives et de leurs questionnements. Le premier Colloque eut lieu en 1957 en présence d universitaires juif comme Edmond Fleg, André Néher, Eliane Amado Lévy-Valensi, Léon Askénazi, Vladimir Jankélévitch, Emmanuel Lévinas ou Jean Wahl. Le succès de la première édition leur permit d en organiser d autres. Les Colloques se succédèrent annuellement, puis tous les deux ans, soit près de trente-huit rencontres jusqu à la fin du XXe siècle. Les communications soulevaient des problèmes contemporains qui agitaient la conscience juive : la politique, la guerre, ou le Shabbat et Israël. La guerre des Six-Jours et l émigration vers Israël de personnalités charismatiques du Comité préparatoire laissa la scène intellectuelle esseulée. Graduellement, l élément marquant du renouveau de la pensée juive française de l après-guerre, devenu une véritable institution avec ses règles et ses habitudes, commença à s essouffler. Dès lors, la symbiose judéo-universelle que les intellectuels juifs de l après-guerre avaient souhaité unifier au sein du Colloque des intellectuels juifs de langue française laissait la place à une autre définition de l identité juive, en devenir à la fin du XXe siècle.One cannot possibly declare oneself as a Jew by the end of the war. Starting from 1957, Symposium of French speaking Jewish intellectuals meets in order to think over about the meaning of Judaism in contemporary France, with moreover a feeling of bruised citizenship. Initiated by Edmond Fleg and Leon Algazi, they gather many Jewish intellectuals who choose to start again from tradition as a question about their condition as modern men. First closely related to Orsay School, many members of which appear in these meetings. The link with history ans messianism represents the heart of their questionings.PARIS-EPHE-Sciences religieuses (751052336) / SudocSudocFranceF

A simple theory for the modulation of tropical instability waves by ENSO and the annual cycle

International audienceMotivated by a recent active period of Tropical Instability Waves (TIWs) that followed the extreme 2015/2016 El Niño, we developed a stochastically forced linear model for TIWs with its damping rate modulated by the annual cycle and El Niño Southern Oscillation (ENSO). The model's analytical and numerical solutions capture relatively well the observed Pacific TIWs amplitude variability dominated by annual and ENSO timescales. In particular, our model reproduces the seasonal increase in TIWs variance during summers and falls and the nonlinear relationship with the ENSO phase characterised by a suppression, respectively increase of TIW activity during El Niño, respectively La Niña. A substantial fraction of TIWs amplitude modulation emerges from the deterministic nonlinear interaction between ENSO and the annual cycle. This simple mathematical formulation allows capturing the nonlinear rectifications of TIWs activity onto the annual cycle and ENSO through, for instance, TIWs-induced ocean heat transport. Moreover, our approach serves as a general theoretical framework to quantify the deterministic variability in the covariance of climate transients owing to the combined modulation of the annual cycle and ENSO

Battery & Energy Management by Real-Time Model-based Optimisations

International audienceDigital Models for Mechanics, Power Train, Power Sources, Generators, Converters and Electrical Consumers are today developed and used in a large extend, for simulation and validation in different industrial domains. In Automotive applications, the increasing use of electronics and electrical modules lead to a more and more complex on-board powertrain & power-net in a serial production car. In that context, for a better durability and cost reduction, main problems to face are: engine & powertrain optimization, battery sizing, miss-discharge preservation, diagnosis of electric components, consumption optimization, and more generally on energy management. For this purpose, models are helpful used for preliminary off-line analysis and optimization. But in standard automotive on-board controllers, only pre-defined (mapped) outputs are implemented, mainly because of real-time constraints of serial µ-controllers and lack of adequate algorithms development. The real-time optimization described in this paper is applied to Battery Management Systems and to Vehicle Energy Management Systems, based on internal models of battery and of electrical consumers. The optimization strategy depends on the driver request, on the external driving conditions, on the current running point efficiency of the powertrain (combustion engine, electrical motor with or without automated transmission), and on the electrical status (battery state of charge, alternator efficiency, electrical consumers characteristics). For this purpose, a new approach is described in this paper, using model-based algorithms. The optimization is on-line computerized with fast ‘internal simulation’ of the global system. Kind of recursive algorithms can then provide the optimal solutions at each sample time. Main advantages of the model-based optimization are: a better performance (results are tested at each sample time), a better robustness to deviations (the internal models can be auto-adapted), and a better flexibility and maintainability, since any modification of any component of the global vehicle system can be simply translated in modifications of the internal models. Thus, the optimization algorithms themselves are not modified, and any long re-tuning is no more necessary. The direct application concerns a more robust battery diagnosis and electrical power-net control, for energy use optimization. Some simulation and real tests are described, which provide promising results, able to improve significantly the energy use in a vehicle. Applications are wide open: for automotive powertrain & power-net management as described here, as well as for many other industrial applications, as aerospace electrical control, building lighting, handy phones, etc

Hybrid vehicle efficiency optimization on a planned trip

International audienceThe stringent fuel consumption and pollutants reduction standards enforce manufacturers and carmakers to have a closer look on new powertrain architectures for individual vehicles. In that context, studies on hybrid vehicles appear today in a substantial scale. The association of a high efficiency electrical motor with an internal combustion engine needs specific control laws in order to optimize the energy management.This paper presents a new control strategy developed by SiemensVDO Automotive and the LEEI laboratory on an electrical parallel hybrid vehicle. A supervisor is built to have a full control of the drive train (clutch, gearshifts, thermal IC engine torque and electrical motor torque) to improve fuel consumption and to maintain an admissible battery state of charge. The optimization algorithm is realized on the overall trip. An offline global optimization is made to analyze the main optimal behavior of the system. The results of that analysis are associated to an onboard navigation system that provides information on the vehicle environment, traffic, distance and road type between the starting point and the destination of the planned trip. Such information is used to analyze the different phases of the trip and to determine a vehicle speed profile and torque needs during the trip, for a better battery management with larger electrical motor torque possibilities. It will also provide optimal gear ratio that can be applied knowing the future acceleration constrains. This includes the concept of driveability in our criterion that is often in contradiction with energy savings.It is clear that this strategy is not intended to calculate the global optimal solution. But we hope to obtain greater reduction of fuel consumption by adding trip prediction to the supervision system, instead of an offline tuning of mapped working points

On the key influence of remote climate variability from Tropical Cyclones, North and South Atlantic mid-latitude storms on the Senegalese coast (West Africa)

International audienc