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  • 1
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    Lagrangian temperature and vertical velocity fluctuations due to gravity waves in the lower stratosphere (2016)
    Wiley
    Details
    Publication Date: 2016-03-23
    Description: Wave-induced lagrangian fluctuations of temperature and vertical velocity in the lower stratosphere are quantified using measurements from superpressure balloons (SPBs). Observations recorded every minute along SPB flights allow the whole gravity-wave spectrum to be described, and provide unprecedented information on both the intrinsic-frequency spectrum and the probability distribution function of wave fluctuations. The dataset has been collected during two campaigns coordinated by the French Space Agency in 2010, involving 19 balloons over Antarctica and 3 in the deep tropics. In both regions, the vertical-velocity distributions depart significantly from a Gaussian behavior. Knowledge on such wave fluctuations is essential for modeling microphysical processes along Lagrangian trajectories. We propose a new simple parameterization that reproduces both the non-Gaussian distribution of vertical velocities (or heating/cooling rates) and their observed intrinsic-frequency spectrum.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Evaluating the advective Brewer-Dobson circulation in three reanalyses for the period 1979–2012 (2015)
    Wiley
    Details
    Publication Date: 2015-06-20
    Description: Most chemistry-climate models show an intensification of the Brewer-Dobson circulation (BDC) in the stratosphere associated with increasing greenhouse gas emissions and ozone depletion in the last decades, but this trend remains to be confirmed inobservational data. In this work the evolution of the advective BDC for the period 1979–2012 is evaluated and compared in three modern reanalyses (ERA-Interim, MERRA and JRA-55). Three different estimates of the BDC are computed for each reanalysis, one based on the definition of the residual circulation and two indirect estimates derived from momentum and thermodynamic balances. The comparison among the nine estimates shows substantial uncertainty in the mean magnitude (~40%) but significant common variability. The tropical upwelling series show variability linked to the stratospheric Quasi-Biennial Oscillation (QBO) and to El Nino-Southern Oscillation (ENSO), and also reflect extreme events such as major Sudden Stratospheric Warmings (SSW) and volcanic eruptions. The trend analysis suggests a strengthening of tropical upwelling of around 2-5%/decade throughout the layer 100–10 hPa. The global spatial structure of the BDC trends provides evidence of an overall accelerationof the circulation in both hemispheres, with qualitative agreement among the estimates. The global BDC trends are mainly linked to changes in the boreal winter season and can be tracked to long-term increases in the resolved wave drag in both hemispheres.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    Interannual variability in effective diffusivity in the upper troposphere / lower stratosphere from reanalysis data (2016)
    Wiley
    Details
    Publication Date: 2016-03-04
    Description: The effective diffusivity based on passive tracer advection is used to evaluate the long-term mixing properties for the period 1980–2012 in the lower stratosphere and upper troposphere (UTLS) using data from the ERA-Interim reanalysis. The regions of strongest interannual variability in effective diffusivity coincide with the regions of strong climatological mixing, such as the winter and spring midlatitude stratosphere, the polar lowermost stratosphere and around the edge of the subtropical jets (especially in summer). The annular modes dominate the variability within the winter polar vortices, and the Quasi-Biennial Oscillation in the tropical stratosphere. El Niño/Southern Oscillation modulates the strength of mixing across the subtropical jets, and has a significant impact onmixing in the summer subtropical lower stratosphere. Long-term trends show a vertical shift in the mixing consistent with the effect of ozone depletion on the zonal wind in the austral summer polar stratosphere. Other significant trends include increased mixing in the austral surf zone and a dipolar pattern in the boreal summer and fall, with mixing increased on the equatorward part of the subtropical jet and reduced just above. The results are highly consistent with those from the JRA-55 reanalysis when the same horizontal resolution is used. The calculations are also qualitatively consistent with effective diffusivity obtained directly from the potential vorticity field and, in the UTLS, they are broadly consistent with those obtained from the ozone field.
    Print ISSN: 0035-9009
    Electronic ISSN: 1477-870X
    Topics: Geography , Physics
    Published by Wiley
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  • 4
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    Geosciences, Vol. 7, Pages 84: Assessment of the Combined Sensitivity of Nadir TIR Satellite Observations to Volcanic SO2 and Sulphate Aerosols after a Moderate Stratospheric Eruption (2017)
    MDPI Publishing
    Details
    Publication Date: 2017-09-14
    Description: Geosciences, Vol. 7, Pages 84: Assessment of the Combined Sensitivity of Nadir TIR Satellite Observations to Volcanic SO2 and Sulphate Aerosols after a Moderate Stratospheric Eruption Geosciences doi: 10.3390/geosciences7030084 Authors: Henda Guermazi Pasquale Sellitto Mohamed Serbaji Bernard Legras Farhat Rekhiss Monitoring gaseous and particulate volcanic emissions with remote observations is of particular importance for climate studies, air quality and natural risk assessment. The concurrent impact of the simultaneous presence of sulphur dioxide (SO2) emissions and the subsequently formed secondary sulphate aerosols (SSA) on the thermal infraRed (TIR) satellite observations is not yet well quantified. In this paper, we present the first assessment of the combined sensitivity of pseudo-observations from three TIR satellite instruments (the Infrared Atmospheric Sounding Interferometer (IASI), the MODerate resolution Imaging Spectro radiometer (MODIS) and the Spinning Enhanced Visible and InfraRed Imager (SEVIRI)) to these two volcanic effluents, following an idealized moderate stratospheric eruption. Direct radiative transfer calculations have been performed using the 4A (Automatized Atmospheric Absorption Atlas) radiative transfer model during short-term atmospheric sulphur cycle evolution. The results show that the mutual effect of the volcanic SO2 and SSA on the TIR outgoing radiation is obvious after three to five days from the eruption. Therefore, retrieval efforts of SO2 concentration should consider the progressively formed SSA and vice-versa. This result is also confirmed by estimating the information content of the TIR pseudo-observations to the bi-dimensional retrieved vector formed by the total masses of sulphur dioxide and sulphate aerosols. We find that it is important to be careful when attempting to quantify SO2 burdens in aged volcanic plumes using broad-band instruments like SEVIRI and MODIS as these retrievals present high uncertainties. For IASI, the total errors are smaller and the two parameters can be retrieved as independent quantities.
    Electronic ISSN: 2076-3263
    Topics: Geosciences
    Published by MDPI Publishing
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  • 5
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    Transferts culturels et politiques dans le monde hellénistique : Actes de la table ronde sur les identités collectives (Sorbonne, 7 (2021)
    Éditions de la Sorbonne
    Details
    Publication Date: 2024-03-25
    Description: L'ère hellénistique qui vit le monde grec s'étendre sur une grande partie de la « terre habitée » offre un cadre exceptionnel pour l'étude de la théorie des transferts culturels. Ce livre issu d'une journée d'études en Sorbonne rassemblant des historiens de l'antiquité a pour ambition d'éprouver la pertinence de ce concept encore jeune. Il place le politique au cœur de sa réflexion, car celui-ci permet d'ouvrir la discussion sur des univers qui lui sont indissolublement liés, en particulier le monde institutionnel, le monde juridique et le monde religieux qu'il soit polythéiste païen ou monothéiste juif. La période hellénistique pose de fait une problématique triangulaire, favorable à l'étude du jeu des transferts entre trois pôles : le pouvoir royal des souverains hellénistiques, les cités grecques, anciennes et nouvelles, et les pouvoirs non grecs, qu'il s'agisse des diverses communautés « indigènes », y compris les temples et les sanctuaires, ou bien encore des Romains, tous variablement récepteurs, vecteurs ou bien émetteurs d'éléments culturels, matériels ou immatériels, façonnant leurs propres identités. Il s'est agi de faire le point sur des dossiers importants en associant des synthèses et des exemples précis mettant en scène la problématique dégagée : « le politique et les institutions », « le politique et le droit », « le politique et la religion ». Cette rencontre scientifique, qui s'est voulue dialectique, n'a cependant nullement épuisé la perspective dégagée par les six enquêtes réunies en ce volume : contribuer au débat historique actuel en revisitant avec un regard aussi neuf que possible des phénomènes de réception réciproque qui fondent l'hellénisme.
    Keywords: D1-2009 ; époque hellénistique ; institution ; politique ; théorie des transferts culturels ; Antiquité ; religion ; thema EDItEUR::D Biography, Literature and Literary studies::D Biography, Literature and Literary studies::DN Biography and non-fiction prose
    Language: French
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  • 6
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    Transferts culturels et droits dans le monde grec et hellénistique (2021)
    Éditions de la Sorbonne
    Details
    Publication Date: 2024-03-25
    Description: Le colloque international Transferts culturels et droit dans les mondes grec et hellénistique étudie les phénomènes de réceptions, d'emprunts et d'adaptations dans la sphère juridique, depuis la naissance du droit grec, à l'époque archaïque durant l'âge des législateurs, jusqu'à l'établissement du pouvoir romain sur l'espace méditerranéen. La problématique envisagée a permis des échanges entre spécialistes venus d'horizons différents, historiens, juristes, anthropologues, hellénistes, romanistes, démotisants, sémitisants, orientalistes, dont les regards sur le monde grec et hellénistique sont complémentaires. Leurs deux préoccupations principales ont été, d'une part, de revenir sur les dynamiques juridiques internes au monde grec et, d'autre part, de mesurer les influences réciproques des droits des mondes grecs et des mondes « barbares ». Ce colloque complète et approfondit une première rencontre organisée en Sorbonne, durant l'année 2004 sur le thème Transferts culturels et politique dans le monde hellénistique (Jean-Christophe Couvenhes et Bernard Legras éd., Publications de la Sorbonne, 2006). L'histoire juridique de la Méditerranée antique sur un temps long permet en effet de mesurer comment l'élargissement du monde grec avec la conquête d'Alexandre, puis la formation de l'Empire mondial des Romains ont suscité l'élaboration d'une koinè juridique, qui a offert à des peuples de traditions différentes de vivre globalement en paix dans des sociétés pour l'essentiel multiculturelles.
    Keywords: D1-2009 ; époque hellénistique ; koinè juridique ; Empire romain ; monde barbare ; droit grec ; histoire juridique ; espace méditerranéen ; thema EDItEUR::D Biography, Literature and Literary studies::D Biography, Literature and Literary studies::DN Biography and non-fiction prose
    Language: French
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  • 7
    Electronic Resource
    Electronic Resource
    The elliptical model of two-dimensional vortex dynamics. II: Disturbance equations (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 855-869 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In Part I [Phys. Fluids A 3, (square, solid)(square, solid)(square, solid) (1991)] approximate equations were developed describing the basic evolution of vortices in a general strain field. These equations take the form of a set of coupled, nonlinear ordinary differential equations describing the time evolution of the centroids, aspect ratios, and orientations of a nested set of elliptical contours representing each vortex. Here, in Part II, the model is extended to include disturbances to the elliptical shape of each contour, disturbances that are excited naturally by the interaction with other vortices. This interaction is worked out explicitly for the first time. The final equations obtained decouple into sets of equations for each mode symmetry, allowing for a very simple description of the disturbance evolution. Numerical tests show remarkable agreement between the elliptical model and the full equations of motion in four problems: (1) the equilibrium contour shapes of a multicontour family of vortices, (2) the linear stability of this family, (3) the equilibrium, nonelliptical shapes of two corotating vortex patches, and (4) the interaction between two symmetrical vortex patches, including merging.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858016
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    Paper (German National Licenses)
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  • 8
    Electronic Resource
    Electronic Resource
    Vortex stripping and the erosion of coherent structures in two-dimensional flows (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 6 (1994), S. 3954-3962 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This paper studies the erosion of a monotonically distributed vortex by the joint action of inviscid stripping, induced by an externally imposed adverse shear, and viscous diffusion, either in the form of Newtonian viscosity or hyperviscosity. It is shown that vortex erosion is greatly amplified by the presence of diffusion; abrupt vortex breakup or gradual quasi-equilibrium evolution depend crucially on the strain to peak vorticity ratio and on the Reynolds number. Peculiar, unexpected effects are observed when hyperviscosity is used in place of Newtonian viscosity. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.868385
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  • 9
    Electronic Resource
    Electronic Resource
    The elliptical model of two-dimensional vortex dynamics. I: The basic state (1991)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 3 (1991), S. 845-854 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An approximate model of nonaxisymmetric vortices in a two-dimensional fluid is developed in which each vortex is assumed to consist of a nested stack of elliptical regions of uniform vorticity. The model is governed by a set of coupled nonlinear ordinary differential equations for the aspect ratio, orientation, and centroid of the bounding contour of each region. It also admits a Hamiltonian formulation and possesses all the invariants of the original system. In Part II [Phys. Fluids A 3, XXX (1991)], the model is extended to include disturbances to the elliptical shape of each contour.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858015
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  • 10
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    Dispersive and friction-induced stabilization of the Cahn–Hilliard inverse cascade (2003)
    Elsevier
    Details
    Publication Date: 2003-02-01
    Print ISSN: 0167-2789
    Electronic ISSN: 1872-8022
    Topics: Physics
    Published by Elsevier
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