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Inventing/Inverting Grand Paris. Towards new metropolitan histories?
No full textInternational audienceThe political moment triggered by the Grand Paris international consultation process of 2008 provided an exceptional opportunity to revive research into the history of the Paris Region. Researchers could not help but question the discourse stressing a break with the past promoted then by decision-makers, developers and the media. It was in this spirit that the multidisciplinary research group “Inventer le Grand Paris” (Inventing Grand Paris) was formed in 2012. The word « inventing », understood according to its dual etymology of inventory and invention, has made it possible to renew a number of elements. The first was to move beyond an older historiography that used the succession of major development plans as the main framework that shaped the metropolis’ narrative. The second was to place the example of Paris firmly within an international comparative perspective, highlighting the circulation of knowledge and experts, and analysing the possible ‘moments’ around which common issues become focused within an overlapping history of metropolises. The third consisted of enriching the history of the metropolitan phenomenon with other issues, such as political scenes, landscapes and representations, as well as long-term development.So why add the word ‘inverting’ here? On the one hand, the work of the research group has led to a shift in focus towards multi-faceted approaches to Grand Paris : to the single object of study that has sometimes been placed in a comparative perspective, succeeds one made of multiple areas, brought together by the research question they grapple with. On the other hand, the increasing importance in political and media discourse, as well as in academic disciplines, of environmental concerns, of heritage awareness, of the interests for users or stakeholders who previously played only a minor role, or the growing interest for the situated narrative, are all invitations to adopt a more decentralised perspective as a means of grasping the metropolitan phenomenon. The word « inverting » here explores the potential for the renewal of research in the dual sense of « inverting the perspective » and « changing order and value »
A framework to assess climate change effects on surface air temperature and soil moisture and application to Southwestern France
No full textInternational audienceA comprehensive framework for climate change assessment is a prerequisite for managing multiple risks related to climate extremes, such as droughts, floods, or compound extreme events. It is also useful for addressing the diverging interests of stakeholders in finding regional adaptation solutions. Here, we design such a framework and a general methodology to assess the evolution of regional climate. Both mean values and extreme event characteristics of surface air temperature and soil moisture are analysed, including the likelihood of compound hot-dry, hot-wet, cold-dry, and cold-wet extreme conditions. These analyses are conducted for each month to investigate a variety of climate change impacts. The methodology is designed to be generic and easily applicable to any region of the world. It provides a foundational basis for initiating dialogue with local decisionmakers, which will subsequently allow for further refinement of climatic impact-driver indices and analyses to produce tailored climate services. This work reports an application to Southwestern France, a region vulnerable to both floods and droughts with severe impacts on natural ecosystems and human societies. It foresees a drying and warming throughout the year, more pronounced in summer. It highlights the complexity of designing adaptation solutions and the need for in-depth and comprehensive analyses of the evolution of local climate conditions. Specifically, Southwestern France is expected to experience an increase in drought frequency and intensity, while the region might still have to cope with the opposite phenomenon, floods
On the resolution of cross-liabilities
No full textInternational audienceIn a variety of systems, in particular in a financial system, entities hold liabilities on each other. The reimbursement abilities are intertwined, thereby potentially generating coordination failures and cascades of defaults calling for orderly resolution. With a single indebted firm, a bankruptcy law organizes such an orderly resolution. With cross-liabilities, a resolution rule should be defined at the system level to account for all those affected, directly or indirectly. This paper investigates such rules assuming their primary goal is to avoid defaults on creditors external to the system, say banks’ defaults on customers’ deposits. I define and characterize the constrained-proportional rule building on two approaches: the minimization of an inequality measure on the reimbursements (made and received) and the axiomatization through desirable properties
« La circulation des modèles : illusion ou inspiration ? Une question d’échelle ou de compétence », dossier "La marche en ville : vers l’invention d’unepolitique publique ?"
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An Empirical Parameterization of the Subgrid‐Scale Distribution of Water Vapor in the UTLS for Atmospheric General Circulation Models
No full textInternational audienceTemperature and water vapor are known to fluctuate on multiple scales. In this study 27 years of airborne measurements of temperature and relative humidity from In‐service Aircraft for a Global Observing System (IAGOS) are used to parameterize the distribution of water vapor in the upper troposphere and lower stratosphere. The parameterization is designed to simulate water vapor fluctuations within gridboxes of atmospheric general circulation models (AGCMs) with typical size of a few tens to a few hundred kilometers. The distributions currently used in such models are often not supported by observations at high altitude. More sophisticated distributions are key to represent ice supersaturation, a physical phenomenon that plays a major role in the formation of natural cirrus and contrail cirrus. Here the observed distributions are fitted with a beta law whose parameters are adjusted from the gridbox mean variables. More specifically the standard deviation and skewness of the distributions are expressed as empirical functions of the average temperature and specific humidity, two typical prognostic variables of AGCMs. Thus, the distribution of water vapor is fully parameterized for a use in these models. The new parameterization reproduces the observed distributions with a determination coefficient always greater than 0.917 and with a mean value of 0.997. The parameterization is robust to a selection of various geographical subsets of data and to gridbox sizes varying between 25 and 300 km
Comment comprendre la cause principale du changement climatique avec un minimum de prérequis ?: Proposition de nouvelles expériences et d’une logique de construction du lien entre l’augmentation de la concentration en CO2 dans l’atmosphère et le réchauffement global
No full textInternational audienceThis article proposes a logic of construction of the link between the increase in CO2 concentration in the atmosphere and global warming. Establishing this link provides an initial qualitative argument for understanding the human origin of climate change, prior to understanding the climate models used to establish this knowledge. The central aim of this approach is to make it accessible with a minimum of conceptual prerequisites, so that it can be used with non-specialists, particularly in the context of science teaching in the final year of general education (in France). This proposal is based on a joint analysis of the physical content, existing teaching approaches and the difficulties experienced by students. The logic developed implies first of all a construction of the notion of infrared radiation, in order to be able to interpret pictures of CO2 and air balloons observed with an infrared camera. By extrapolating these observations to the Earth system, it is possible to understand the effect of adding CO2 to its radiation balance. We argued that this explanation, at this level, can only be rigorously carried out with a radiation balance restricted to exchanges between the Earth system and Space (without considering those with the atmosphere).Nous proposons dans cette étude une approche d’enseignement du réchauffement climatique adaptée aux nouveaux programmes de lycée général et professionnel. L’objectif visé est la construction du lien entre augmentation de la concentration en CO 2 et élévation de la température moyenne de la Terre, en s’appuyant autant que possible sur des éléments empiriques explicites. Nous présentons dans un premier temps les approches d’enseignement existantes sur le sujet, qui sont ensuite mises en relation avec les idées et modes de raisonnement connus des élèves, en particulier : la non-évidence des interactions entre gaz et rayonnement. Les choix didactiques structurant le cheminement conceptuel proposé sont alors exposés. Ils s’articulent autour de l’interprétation d’expériences réalisées avec une caméra infrarouge permettant de mettre en évidence l’émission et l’absorption du rayonnement infrarouge par le CO
Droits fonciers familiaux, désir de propriété et circulation de l’argent. Trois logiques de transformations foncières ordinaires dans les franges métropolitaines du Sud du Bénin
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Multi-Criteria Optimization of Distributed Real-Time Network Topologies
No full textInternational audienceCommunication needs in avionics and transportation have radically changed over the recent years. Traditionally, the underlying hard real-time networks were designed in a centralized way, focusing on redundancy and isolation. Today, real-time communication is ubiquitous, from large airplanes to small vehicles. The associated networks must support a wide range of applications, and large amounts of data. Centralized approaches from the avionics domain, e.g., AFDX, are too costly, too heavyweight, and not flexible enough for these applications.In this paper we explore a new distributed network architecture designed to support jumbo airliners, but also small aircraft and drones. Communication redundancy is achieved using redundant paths, which have to be adapted and optimized to the application. The main challenge then is to build an optimized network configuration ensuring safety, fault tolerance, timing, and performance of both critical, and non-critical communication. Minimizing volume and weight of the equipment is also mandatory. Since the solution space is too large to be explored in reasonable time, we propose a genetic algorithm. Our experiments show that our algorithm converges quickly and offers solutions of excellent quality. The computed solutions are in the top 2% among the best solutions obtained using an exhaustive exploration. Our approach thus enables system engineers to quickly explore and choose very good solution for their systems
Global ocean carbon uptake enhanced by rainfall
No full textInternational audienceRain alters local sea surface physical and biogeochemical properties but its spatiotemporal variability has led to its overlook in global ocean carbon uptake studies. Different physical and chemical processes in the gaseous and liquid phases control the transfer of carbon dioxide (CO2) between the atmosphere and ocean. Rain impacts the interfacial flux by (1) increasing turbulence in the ocean and (2) modulating the air–sea CO2 concentration gradient. Concurrently, raindrops inject CO2 absorbed during their fall into the ocean through wet deposition. Here this study presents a comprehensive estimate of these effects on the global ocean carbon uptake over 2008–2018 based on observational products (satellite and in situ) and reanalysis. Using various representations of the ocean surface response to rainfall and different rain products, we show that rain increases the ocean carbon sink by +0.14–0.19 PgC yr‑1 over 2008–2018, representing an increase of 5–7% of the ocean carbon uptake (2.66 PgC yr‑1). Rain-induced interfacial flux and wet deposition have comparable orders of magnitude. The former mainly increases the CO2 sink in the tropics because strong rain rates and weak winds induce noticeable salinity and CO2 dilution. The latter is important in the tropics, storm track regions and the Southern Ocean
Influence of Natural External Forcings on Interdecadal Variation of Global Land Monsoon over the Last Millennium in CESM-LME
No full textInternational audienceInterdecadal variations of the global land monsoon have been previously attributed to internal fluctuations of the climate system, but the role of natural external forcings was underexplored. Here, we investigate this issue by using the Community Earth System Model ensemble simulations over the last millennium (LM) (AD 950-1850). Our analysis reveals that the surface temperature, with two dominant structures (global cooling/warming and longitudinal sea surface temperature gradient in the tropical Pacific, which affects the Walker circulation), predominantly shapes the leading forced mode of the global land monsoon. This mode, representing 19% of the total variance, manifests as consistent features across South Asia, the southern part of East Asia, North Australia, South America, and western South Africa, contrasting with other monsoon regions. Under global cooling conditions, the monsoon intensity is enhanced in the northern parts of the East Asian and eastern parts of the North and South African monsoons, but it decreases in the other monsoon regions. Under weak Walker circulation conditions, changes in atmospheric circulation in response to the sea surface temperature gradient in the tropical Pacific are associated with a substantial attenuation of almost all land monsoon regions. It was further shown that the global mean surface temperature and the tropical Pacific temperature gradient jointly account for 75% of the total variance in the leading mode of the global land monsoon, with 29% and 46% as their respective contributions. Furthermore, our results suggest that volcanic eruptions are the dominant external forcing for these variations. These findings provide valuable insights for future research on global monsoon dynamics