Combination of WENO and Explicit Runge–Kutta Methods for Wind Transport in the Meso-NH Model

This paper investigates the use of the weighted essentially nonoscillatory (WENO) space discretization methods of third and fifth order for momentum transport in the Meso-NH meteorological model, and their association with explicit Runge–Kutta (ERK) methods, with the specific purpose of finding an optimal combination in terms of wall-clock time to solution. A linear stability analysis using von Neumann theory is first conducted that considers six different ERK time integration methods. A new graphical representation of linear stability is proposed, which allows a first discrimination between the ERK methods. The theoretical analysis is then completed by tests on numerical problems of increasing complexity (linear advection of high wind gradient, orographic waves, density current, large eddy simulation of fog, and windstorm simulation), using a fourth-order-centered scheme as a reference basis. The five-stage third-order and fourth-order ERK combinations appear as the time integration methods of choice for coupling with WENO schemes in terms of stability. An explicit time-splitting method added to the ERK temporal scheme for WENO improves the stability properties slightly more. When the spatial discretizations are compared, WENO schemes present the main advantage of maintaining stable, nonoscillatory transitions with sharp discontinuities, but WENO third order is excessively damping, while WENO fifth order provides better accuracy. Finally, WENO fifth order combined with the ERK method makes the whole physics of the model 3 times faster compared to the classical fourth-order centered scheme associated with the leapfrog temporal scheme

Interaction d'un cyclone tropical avec une onde de Rossby planétaire

La migration d'un cyclone tropical aux moyennes latitudes est un problème récurrent pour les modèles de prévision du temps. En particulier, l'interaction entre un cyclone tropical et une onde de Rossby planétaire réduit la prévisibilité en aval. Une simulation numérique avec le modèle atmosphérique Méso-NH reproduit cette interaction d'échelle grâce à sa résolution kilométrique étendue à une domaine semi-hémisphérique. Cette résolution élevée permet pour la première fois de décrire explicitement les phénomènes fortement diabatiques associés à la convection du cyclone

Modélisation numérique de la méso-échelle á l’échelle des LES: interactions entre la dynamique et la physique

Atmospheric research relies on observation and modeling tools. Among the modeling tools, mesoscale models allow atmospheric simulations at resolutions of a few kilometers to a few meters. An atmospheric model represents both resolved features (through the dynamical core) and unresolved or under-resolved processes (through the physical parameterizations). The interactions between dynamics and physics are essential and complex. Submesh patterns and spatial resolution must complement each other, leading to the notion of "seamless" physics. It is necessary to progress simultaneously on the dynamic core and the numerical schemes, the physical parameterizations, and their interactions.The improvement of the dynamics of the Meso-NH research model has been one of our objectives, with in particular the renovation of the numerical schemes to gain in computation time while ensuring a good level of accuracy. It was also a question of developing the faculties of use of the model in LES (Large Eddy Simulation) mode for real cases. The second objective is to improve the representation of clouds and precipitation through physical parameterizations for the AROME and Meso-NH models, in terms of microphysics and macrophysics. It also appeared important to improve the turbulence in deep convective clouds, currently under-represented at kilometer scales. The approach is based on process studies conducted with Meso-NH on various phenomena, such as fog, stratocumulus to cumulus transitions or extra-tropical transitions. Developing new couplings in the framework of multidisciplinary collaborations has also been an opportunity to address other societal issues related to meteorology, such as the propagation of forest fires or the dispersion of pollutants.Finally, perspectives to this research work are presented.La recherche atmosphérique repose sur des moyens d'observation et de modélisation. Parmi les outils de modélisation, les modèles de méso-échelle permettent des simulations atmosphériques à des résolutions de quelques kilomètres à quelques mètres. Un modèle atmosphérique représente à la fois des caractéristiques résolues (grâce au coeur dynamique) et des processus non résolus ou sous-résolus (par les paramétrisations physiques). Les interactions entre la dynamique et la physique sont essentielles et complexes. Schémas sous-maille et résolution spatiale doivent se compléter, menant à la notion de physique « sans couture ». Il est nécessaire de progresser simultanément sur le coeur dynamique et les schémas numériques, les paramétrisations physiques, ainsi que leurs interactions.L’amélioration de la dynamique du modèle de recherche Méso-NH a constitué l’un de nos objectifs, avec notamment la rénovation des schémas numériques pour gagner en temps de calcul tout en assurant un bon niveau de précision. Il s’est agi également de développer les facultés d’utilisation du modèle en mode LES (Large Eddy Simulation) pour des cas réels. Le second objectif est d’améliorer la représentation des nuages et des précipitations au travers des paramétrisations physiques pour les modèles AROME et Méso-NH, en terme de microphysique et de macrophysique. Il est aussi apparu important d'améliorer la turbulence dans les nuages convectifs profonds, actuellement sous-représentée aux échelles kilométriques. La démarche s'appuie sur des études de processus menées avec Méso-NH sur des phénomènes variés, comme le brouillard, les transitions de stratocumulus à cumulus ou les transitions extra-tropicales. Développer de nouveaux couplages dans le cadre de collaborations pluridisciplinaires a également constitué une opportunité d'aborder d'autres sujets sociétaux en lien avec la météorologie, comme la propagation des feux de forêt ou la dispersion de polluants.Des perspectives à ces travaux de recherche sont enfin présentés

Women and children first: A comparative study of Louisa May Alcott and Sophie de Segur (Rostopchine)

The purpose of this dissertation is to determine why Louisa May Alcott and Sophie de Segur, two prominent writers of children\u27s literature of the nineteenth century, have been deleted from the canon by critics at large. I have used several approaches to analyze the art of Alcott and Segur. Studying biographical elements show how exceptional both women were in their own time. Each author was raised by parents who defied the established social order; each author battled with illness, grief, and isolation; each author maintained a very close yet antagonistic relationship with her own mother. The novels produced by Alcott and Segur reflect the events in their own life very closely; yet each one of these fictional testimonies also represent the definite will of the author to beat fate and to rework pain and drudgery into viable solutions. I have examined this specific vision in opposition to nineteenth century writers of the canon (Hawthorne, James, Eliot, Sand, Balzac, Flaubert, and others) and to twentieth century contemporary writers (Duras, Conde, Walker, Ehrdrich) and concluded Alcott and Segur have a more established kinship with very contemporary twentieth century women writers, especially minority writers, than to the male writers of the nineteenth century. The feature that Alcott and Segur have in common with each other and with contemporary women writers is the structure of their text, characterization, and vision according to a process I have called hypallage. This process is based on the reciprocity of influence between events, characters, and thoughts. It emphasizes realistically the fluidity of the fabric of life: one event influences another, a reaction which leads the second event to change the first one in turn. The dialogical and generative nature of this process stresses the non-finality of events. The process creates an open text which is very different from canonical texts where final solutions are the rule. Through this process, the authors are able to describe the probability of success as opposed to the certainty of failure. The literature it creates is then ideally suited to the audience of the young or the powerless, an audience with which the canon has not been truly concerned very often

Editorial

Mias Christine, Lac Michel. Editorial. In: Les dossiers des sciences de l'éducation, N°17, 2007. Travail social et formation : voies pour la professionnalisation. pp. 5-10

Editorial

Mias Christine, Lac Michel. Editorial. In: Les dossiers des sciences de l'éducation, N°17, 2007. Travail social et formation : voies pour la professionnalisation. pp. 5-10

Modélisation micrométéorologique d'un site

National audienc

Dynamique de l'interface nuage-environnement et effets de turbulence dans une LES d'un Cumulus Congestus en croissance

International audienceA giga-large-eddy simulation of a cumulus congestus has been performed with a 5-m resolution to examine the fine-scale dynamics and mixing on its edges. At 5-m resolution, the dynamical production of subgrid turbulence clearly dominates over the thermal production, whereas the situation is reversed for resolved turbulence, the tipping point occurring near the 250-m scale. For cloud dynamics, the toroidal circulation already obtained in previous observational and numerical studies remains, with a strong signature on the resolved turbulent fluxes, the most important feature for the exchanges between the cloud and its environment even though numerous smaller eddies are also well resolved. The environment compensates for the upward mass flux through a large-scale compensating subsidence and the so-called subsiding shell composed of cloud-edge downdrafts, both having a significant contribution. A partition is used to characterize the dynamics, buoyancy, and turbulence of the inner and outer edges of the cloud, the cloud interior, and the far environment. On the edges of the cloud, downdrafts caused by the eddies and by evaporative cooling effects coexist with a buoyancy reversal while the cloud interior is mostly rising and positively buoyant. An alternative simulation in which evaporative cooling is suppressed indicates that this process reinforces the downdrafts near the edges of the cloud and causes a general decrease of the convective circulation. Evaporative cooling also has an impact on the buoyancy reversal and on the fate of the engulfed air inside the cloud