Improving solar wind persistence forecasts: removing transient space weather events, and using observations away from the Sun-Earth line

This study demonstrates two significant ways of improving persistence forecasts of the solar wind, which exploit the relatively unchanging nature of the ambient solar wind to provide 27 day forecasts, when using data from the Lagrangian L1 point. Such forecasts are useful as a prediction tool for the ambient wind, and for benchmarking of solar wind models. We show that solar wind persistence forecasts can be improved by removing transient solar wind features such as coronal mass ejections (CMEs). Using CME indicators to automatically identify CME-contaminated periods in ACE data from 1998 to 2011, and replacing these with solar wind from a previous synodic rotation, persistence forecasts improve (relative to a baseline): skill scores for Bz, a crucial parameter for determining solar wind geoeffectiveness, improve by 7.7 percentage points when using a proton temperature-based indicator with good operational potential. We also show that persistence forecasts can be improved by using measurements away from L1, to reduce the requirement on coronal stability for an entire synodic period, at the cost of reduced lead time. Using STEREO-B data from 2007 to 2013 to create such a reduced lead time persistence forecast, we show that Bz skill scores improve by 17.1 percentage points relative to ACE. Finally, we report on implications for persistence forecasts from any future missions to the L5 Lagrangian point and on the successful operational implementation (in spring 2015) of the normal (ACE-based) and reduced lead time (STEREO-based) persistence forecasts in the Met Office's Space Weather Operations Centre, as well as plans for future improvements

Origins of Negative Gas Adsorption

International audienceNegative gas adsorption by a porous crystalline solid, DUT-49, observed by spontaneous desorption of gas during a pressure increase raises fundamental questions on the physical origin of this puzzling behavior. Importantly, a framework that can transform a large amount of strain into pressure has many possible technological applications. To address this question, we studied the mechanics and thermodynamics of DUT-49 at both the molecular unit and framework scales by applying quantum density functional theory and extensive classical molecular-dynamics simulations. We demonstrate that negative gas adsorption originates from molecular buckling of the organic structural unit and thus allows a colossal framework transformation. Methane adsorption is subsequently shown to activate this transition, in full agreement with experimental observations. The molecular insight presented here unveils the mechanics and thermodynamics responsible for negative gas adsorption and provides unparalleled understanding to aid the discovery of new examples of similarly responsive porous metamaterials

Modélisation numérique et assimilation de données de la dispersion de radionucléides en champ proche et à l'échelle continentale

La justification de l'application de l'assimilation de données à la dispersion de radionucléides découle de la confrontation de modèles aux observations. En champ proche, l'approche variationnelle standard a permis de coupler l'adjoint du modèle de dispersion, pX 0.1, et des mesures collectées dans une soufflerie. Le débit de la source a été inversé. L'optimisation des paramètres de forçage, qui gouverne la forme géométrique du panache, a amélioré l'accord entre les mesures et le modèle. La réduction des réseaux de mesures a été abordée. A l'échelle continentale, la méthode du maximum d'entropie a été utilisée pour reconstruire des sources. Des nouvelles fonctions coût, adaptées au problème, ont été construites. Leur performance a été illustrée sur une série des mesures synthétiques, parfaites et bruitées, générées par le modèle POLAIR 3D. Une méthode opérationnelle de réduction des sites suspectés a été testée. Le profil temporel de la source de l'incident d'Algéciras a été inversé.Model-to-data comparisons justify using data assimilation in dispersion of radionuclides. Near-field measurements collected in a wind tunnel experiment have been coupled to an adjoint of the dispersion model, pX 0.1. Standard variational data assimilation let invert activity rate. Forcing parameters that define the geometric form of the plume, have been optimised and a better model-to-data agreement has been achieved. Reduction of measurement networks has been tackled. At continental scale, the maximum entropy method has been used to invert sources of accidental releases. New, problem-adapted cost functions have been derived. They have been tested on twin experiments using perfect or noisy measurements that have been generated by POLAIR 3D. An operationally useful method of reducing the number of suspected sites has been shown. The temporal profile of the source of Algeciras incident has been inverted.PARIS12-CRETEIL BU Multidisc. (940282102) / SudocSudocFranceF

Angers, Jublains, Le Mans et Nantes. Quatre capitales de cités antiques à l’époque mérovingienne (Ve-VIIe siècles). État des connaissances et actualité des recherches

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Angers, Jublains, Le Mans, Nantes. Quatre chefs-lieux de cités antiques à l’époque mérovingienne. État des connaissances

International audienc

Angers, Jublains, Le Mans, Nantes. Quatre chefs-lieux de cités antiques à l’époque mérovingienne. État des connaissances

International audienc

Angers, Jublains, Le Mans, Nantes. Quatre chefs-lieux de cités antiques à l’époque mérovingienne. État des connaissances

International audienc

Angers, Jublains, Le Mans, Nantes. Quatre chefs-lieux de cités antiques à l’époque mérovingienne. État des connaissances

International audienc