HyMeX: A 10-Year Multidisciplinary Program on the Mediterranean Water Cycle

Drobinski, P. ... et. al.-- 20 pages, 10 figures, 1 table, supplement material http://journals.ametsoc.org/doi/suppl/10.1175/BAMS-D-12-00244.1HyMeX strives to improve our understanding of the Mediterranean water cycle, its variability from the weather-scale events to the seasonal and interannual scales, and its characteristics over one decade (2010–20), with a special focus on hydrometeorological extremes and the associated social and economic vulnerability of the Mediterranean territoriesHyMeX was developed by an international group of scientists and is currently funded by a large number of agencies. It has been the beneficiary of financial contributions from CNRS; Météo-France; CNES; IRSTEA; INRA; ANR; Collectivité Territoriale de Corse; KIT; CNR; Université de Toulouse; Grenoble Universités; EUMETSAT; EUMETNET; AEMet; Université Blaise Pascal, Clermont Ferrand; Université de la Méditerranée (Aix-Marseille II); Université Montpellier 2; CETEMPS; Italian Civil Protection Department; Université Paris- Sud 11; IGN; EPFL; NASA; New Mexico Tech; IFSTTAR; Mercator Ocean; NOAA; ENEA; TU Delft; CEA; ONERA; IMEDEA; SOCIB; ETH; MeteoCat; Consorzio LAMMA; IRD; National Observatory of Athens; Ministerio de Ciencia e Innovación; CIMA; BRGM; Wageningen University and Research Center; Department of Geophysics, University of Zagreb; Institute of Oceanography and Fisheries, Split, Croatia; INGV; OGS; Maroc Météo; DHMZ; ARPA Piemonte; ARPA-SIMC Emilia-Romagna; ARPA Calabria; ARPA Friuli Venezia Giulia; ARPA Liguria; ISPRA; University of Connecticut; Università degli Studi dell'Aquila; Università di Bologna; Università degli Studi di Torino; Università degli Studi della Basilicata; Università La Sapienza di Roma; Università degli Studi di Padova; Università del Salento; Universitat de Barcelona; Universitat de les Illes Balears; Universidad de Castilla-La Mancha; Universidad Complutense de Madrid; MeteoSwiss; and DLR. It also received support from the European Community's Seventh Framework Programme (e.g., PERSEUS, CLIM-RUN)Peer reviewe

Spatial analysis of trend in extreme daily rainfall in southern France

International audienceThis paper makes a regional evaluation of trend in yearly maxima of daily rainfall in southern France, both at point and spatial scales on a regular grid of 8 × 8 km2. In order to filter out the high variability of rainfall maxima, the current analysis is based on a non-stationary GEV modeling in which the location parameter is allowed to vary with time. Three non-stationary models are considered for each series of maxima by constraining the location parameter to vary either linearly, linearly after a given date or linearly up to a final date. Statistical criteria are used to compare these models and select the best starting or final point of putative trends. The analysis shows that, at regional scale, the best distribution of maxima involves a linear trend starting in year 1985 and that this trend is significant in half the region, including most of the mountain ranges and part of the Rhône valley. Increases in yearly maxima are considerable since they reach up more than 60 mm/day in 20 years, which is more than 40 % of the average maximum in this area

A stochastic lightning-flash scheme for 3D explicitly resolving cloud models

International audienceThe paper presents a stochastic lightning-flash scheme designed for mesoscale cloud-resolving models (MCRMs). The lightning-flash scheme is implemented on-line in an MCRM. It is fully parallellized and vectorized. A lightning flash is schematized as two single conducting channels (single tracks) propagating in opposite directions from the lightning ignition point, and of branch patterns propagating from the single tracks. On the base of scale similarities between lightning flashes and discharges in dielectrics at centimetre scales, a stochastic scheme has been designed to compute branch trajectories. A fractal relationship is used to limit the branch number. Charge neutralization operates along the single tracks and branch trajectories to threshold the cloud charge density. The scheme has been implemented in the French meteorological community model M´esoNH. Two kinds of tests were designed to assess the scheme's capabilities. A first set consists of single-lightning simulations, which demonstrate that, thanks to branches, the simulated lightning flashes are (i) able to reach sparse electric charges and (ii) are fractal objects. The second set consists of comprehensive 3D-thundercloud life-cycle simulations. A simple non-inductive charging process is activated in order to assess the sensitivity of thundercloud electrical behaviour to lightning patterns. It is shown that, paradoxically, lightning flashes with quasi-plane branch propagations (i.e. fractal dimension close to 2) lead to more steady electrical behaviour than those completely filling volumes (i.e. fractal dimension close to 3)

Uncertainty estimation of Intensity–Duration–Frequency relationships: A regional analysis

International audienceWe propose in this article a regional study of uncertainties in IDF curves derived from point-rainfall maxima. We develop two generalized extreme value models based on the simple scaling assumption, first in the fre-quentist framework and second in the Bayesian framework. Within the frequentist framework, uncertainties are obtained i) from the Gaussian density stemming from the asymptotic normality theorem of the maximum likelihood and ii) with a bootstrap procedure. Within the Bayesian framework, uncertainties are obtained from the posterior densities. We confront these two frameworks on the same database covering a large region of 100, 000 km 2 in southern France with contrasted rainfall regime, in order to be able to draw conclusion that are not specific to the data. The two frameworks are applied to 405 hourly stations with data back to the 1980's, accumulated in the range 3h-120h. We show that i) the Bayesian framework is more robust than the frequentist one to the starting point of the estimation procedure, ii) the posterior and the bootstrap densities are able to better adjust uncertainty estimation to the data than the Gaussian density, and iii) the bootstrap density give unreasonable confidence intervals, in particular for return levels associated to large return period. Therefore our recommendation goes towards the use of the Bayesian framework to compute uncertainty

Aspects microphysiques et électriques d'un modèle explicite de nuage : description et étude d'un orage académique

An electrification scheme, consistent with the mixed-phase microphysical parameterization, has been developed for the French cloud resolving model MésoNH. There are four successive steps: (i) charge separation is assumed to result only from non-inductive processes; (ii) electrical charges carried by the different hydrometeor species are transported along the air flow and redistributed according to the microphysical processes; (iii) the electric field is deduced from the integration of a modified Poisson equation; (iv) a lightning parameterization simulates triggering, propagation and pseudo-fractal branching of the flashes and associated charge neutralization. Two numerical experiments are conducted firstly to evaluate the performances of the lightning scheme, secondly to test the simulated evolution of the electrical characteristics of a idealized supercellular storm.Un schéma d'électrisation, cohérent avec la paramétrisation microphysique en phase mixte, a été développé pour le modèle numérique de nuage MésoNH. Il y a quatre étapes successives : (i) la séparation de charges est supposée résulter uniquement des processus non-inductifs ; (ii) les charges électriques emportées par les différents types d'hydrométéores sont transportées par le flux atmosphérique et redistribuées par les processus microphysiques ; (iii) le champ électrique est déduit de l'intégration d'une équation de Poisson modifiée ; (iv) une paramétrisation des éclairs simule le déclenchement, la propagation et les branchements pseudo-fractals des décharges et les neutralisations de charge associées. Deux expériences numériques sont conduites, d'abord pour évaluer les performances du schéma d'éclairs, ensuite pour tester l'évolution simulés des caractéristiques électriques d'un orage supercellulaire idéalis

Severe storms in mountainous Mediterranean regions: Uncertainties on extreme rainfall estimations

International audienc

Spatial analysis of extreme rainfalls in the Cévennes-Vivarais region

International audienceThis study takes place in the MedUP project, founded by the ''Agence Nationale de la Recherche'' (French Research Agency) through its VMC program (''Vulnérabilité, Milieux, Climats ''). MedUP deals with the quantification and identification of sources of uncertainties associated with the forecast and climate projection for Mediterranean high-impact weather events. Here, we focus on the estimation of return periods and return levels of extreme rainfalls in the Cevennes-Vivarais region. The hourly data were collected from 142 raingauges located in this region between 1993 and 2000. A first analysis revealed that, the excess rainfall distribution depends on the raingauges location. We propose to model the excess rainfall distribution by a Generalized Pareto Distribution with positive shape parameter depending on geographical covariates. This so-called ''conditional tail-index'' is then estimated with a nearest neighbour approach. This permits to derive return period maps on the region of interest

Development and first results of an explicit electrical scheme in the 3D French mesoscale model "Meso NH"

(9-13 juin 2003

Première analyse des pluies extrêmes dans la région Cévennes-Vivarais

Ce rapport présente l'estimation des périodes et niveaux de retour des pluies ponctuelles en Cévennes-Vivarais. On montre que la loi de Pareto généralisée (GPD) avec un paramètre de forme positif est la mieux adaptée pour modéliser les pluies intenses. Dans la première partie de ce rapport, pour chaque station pluviométrique, on estime les périodes de retour. Les cartes de périodes de retour pour les pluies horaires sont obtenues par krigeage. Dans la seconde partie, on montre que la stationnarité des séries de pluies est erronée. On propose donc un modèle basé sur le découpage de la série temporelle en saisons homogènes