A GPS network for tropospheric tomography in the framework of the Mediterranean hydrometeorological observatory Cévennes-Vivarais (south-eastern France)

International audienceThe Mediterranean hydrometeorological observatory Cévennes-Vivarais (OHM-CV) coordinates hydrometeorological observations (radars, rain gauges, water level stations) on a regional scale in southeastern France. In the framework of OHM-CV, temporary GPS measurements have been carried out for 2 months in autumn 2002, when the heaviest rainfall are expected. These measurements increase the spatial density of the existing permanent GPS network, by adding three more receivers between the Mediterranean coast and the Cévennes-Vivarais range to monitor maritime source of water vapour flow feeding the precipitating systems over the Cévennes-Vivarais region. In addition, a local network of 18 receivers covered an area of 30 by 30 km within the field of view of the meteorological radar. These regional and local networks of permanent and temporary stations are used to monitor the precipitable water vapour (PWV) with high temporal resolution (15 min). Also, the dense local network provided data which have been inverted using tomographic techniques to obtain the 3-D field of tropospheric water vapour content. This study presents methodological tests for retrieving GPS tropospheric observations from dense networks, with the aim of assessing the uncertainties of GPS retrievals. Using optimal tropospheric GPS retrieval methods, high resolution measurements of PWV on a local scale (a few kilometres) are discussed for rain events. Finally, the results of 3-D fields of water vapour densities from GPS tomography are analysed with respect to precipitation fields derived from a meteorological radar, showing a good correlation between precipitation and water vapour depletion areas

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

Mesure des précipitations à l'aide d'un radar en bande X non-cohérent à haute résolution et d'un radar en bande K à visée verticale. Application à l'étude de la variabilité des précipitations lors de la campagne COPS

L estimation quantitative des précipitations à l échelle locale est une nécessité sociétale, à cause de l augmentation des dégâts provoqués par des inondations exacerbées par l urbanisation croissante. Or, des estimations locales sont particulièrement difficiles à réaliser à cause de la forte variabilité des précipitations. De plus, ce genre d estimation est sollicité par de petits organismes tels qu une commune, pour lesquels il n est pas envisageable d utiliser des instruments à la pointe de la recherche technologique à cause de leur coût prohibitif. Ainsi, il est nécessaire de développer des méthodes d estimation quantitative des précipitations applicables à un dispositif expérimental de prix abordable. Dans ce but, un dispositif expérimental innovant est utilisé dans cette thèse. Il est constitué d instruments de mesure directe, au sol, tels que des pluviomètres et des disdromètres, et d un prototype de radar à balayage horizontal basé sur un radar nautique commercial, associé à un MRR (Micro Rain Radar) à visée verticale qui fournissent une estimation en altitude de la pluie, respectivement sur une surface donnée et le long d un profil vertical. Le radar à balayage horizontal est un radar en bande X, c est-à-dire qu il fonctionne à une longueur d onde lui procurant une très haute résolution radiale, mais qui est très atténuée par les précipitations. Le MRR permet d obtenir une description précise de la microphysique des précipitations et sert de relais entre les mesures au sol et les mesures en altitude du radar en bande X. Ces deux radars étant novateurs, une grande partie de cette thèse consiste à valider leurs mesures : étalonnage, filtrage d échos aberrants, correction de l atténuation, etc. Une fois les mesures rendues exploitables, cette thèse se focalise sur l étude de la variabilité des précipitations afin de proposer et développer différentes méthodes de classification, selon leur type ou leur variations locales, et de vérifier leur potentiel pour l amélioration de l estimation des précipitations. Les résultats montrent que cet objectif ne peut être atteint que si la qualité des mesures des radars est encore améliorée : moins d échos parasites pour le radar en bande X et prise en compte du vent vertical pour le MRR.Due to the increase of damage associated with floods enhanced by expanding urbanisation, the quantitative estimation of precipitation on a local scale is a societal need. However, such estimations are difficult because of the high variability of precipitation. Moreover, these estimations are requested by small organisations such as local authorities which cannot afford top level research instruments. Hence, new methods of estimation applicable to a cheap experimental set are needed. Toward this goal, an innovative experimental set is used in this work. It consists of ground instruments such as raingauges and disdrometers, and two radars, a prototype of a scanning radar based on a modified marine radar and a vertically pointing MRR (Micro Rain Radar), which give estimation of rain aloft, over an area and along a profile, respectively. The scanning radar works at X-band, meaning that it uses a longwave very attenuated by precipitation, but which provides a high range resolution. The MRR yields a detailed description of microphysics of precipitation and fills the gap between ground measurements and X-band radar measurements aloft. As both these radars are innovative, a large part of this PhD thesis was spent on the measurements validation : radar calibration, abnormal echoes filtering, attenuation consideration, etc. Using these corrected measurements, this PhD focus then on the study of the variability of precipitation, and aims to propose and develop several classification methods based on precipitation type or local variability, and to check their potential for the improvement of precipitation estimation. Results show that this goal can be reached only if the radar measurements quality is further improved : less interference echoes for the X-band radar, and consideration of vertical wind for the MRR.CLERMONT FD-Bib.électronique (631139902) / SudocSudocFranceF

Estimation des paramètres atmosphériques par GPS (analyse de la variabilité spatio-temporelle de la vapeur d'eau)

La vapeur d'eau joue un rôle important en météorologie.Toutefois, sa variabilité spatio-temporelle a été un frein à son étude. Des chercheurs ont pu mettre en évidence le potentiel du Global Positioning System pour l'étudier. Les résultats sont nombreux. Une distribution 2D grâce aux valeurs intégrées ou une distribution 3D au moyen de la tomographie. Ce travail de thèse présente le logiciel de tomographie troposphérique GPS développé au sein du Laboratoire de météorologie physique. Il fonctionne grâce aux données GPS brutes et aux fichiers météorologiques au sol. L'application opérationnelle est ensuite présentée. Les résultats concernent l'Observatoire Hydrométéorologique des Cévènnes-Vivarais, le réseau GPS permanent de l'Institut Royal Météorologique de Belgique et la campagne Convective and Orographically-induced Precipitation Study. Ces résultats ont fait l'objet d'une étude avec des radars météorologiques afin d'appréhender le rôle de l'humidité pour l'initiation convectiveCLERMONT FD-BCIU Sci.et Tech. (630142101) / SudocSudocFranceF

Geostatistical Merging of a Single-Polarized X-Band Weather Radar and a Sparse Rain Gauge Network over an Urban Catchment

International audienceOptimal Quantitative Precipitation Estimation (QPE) of rainfall is crucial to the accuracy of hydrological models, especially over urban catchments. Small-to-medium size towns are often equipped with sparse rain gauge networks that struggle to capture the variability in rainfall over high spatiotemporal resolutions. X-band Local Area Weather Radars (LAWRs) provide a cost-effective solution to meet this challenge. The Clermont Auvergne metropolis monitors precipitation through a network of 13 rain gauges with a temporal resolution of 5 min. 5 additional rain gauges with a 6-minute temporal resolution are available in the region, and are operated by the national weather service Météo-France. The LaMP (Laboratoire de Météorologie Physique) laboratory's X-band single-polarized weather radar monitors precipitation as well in the region. In this study, three geostatistical interpolation techniques-Ordinary kriging (OK), which was applied to rain gauge data with a variogram inferred from radar data, conditional merging (CM), and kriging with an external drift (KED)-are evaluated and compared through cross-validation. The performance of the inverse distance weighting interpolation technique (IDW), which was applied to rain gauge data only, was investigated as well, in order to evaluate the effect of incorporating radar data on the QPE's quality. The dataset is comprised of rainfall events that occurred during the seasons of summer 2013 and winter 2015, and is exploited at three temporal resolutions: 5, 30, and 60 min. The investigation of the interpolation techniques performances is carried out for both seasons and for the three temporal resolutions using raw radar data, radar data corrected from attenuation, and the mean field bias, successively. The superiority of the geostatistical techniques compared to the inverse distance weighting method was verified with an average relative improvement of 54% and 31% in terms of bias reduction for kriging with an external drift and conditional merging, respectively (cross-validation). KED and OK performed similarly well, while CM lagged behind in terms of point measurement QPE accuracy, but was the best method in terms of preserving the observations' variance. The correction schemes had mixed effects on the multivariate geostatistical methods. Indeed, while the attenuation correction improved KED across the board, the mean field bias correction effects were marginal. Both radar data correction schemes resulted in a decrease of the ability of CM to preserve the observations variance, while slightly improving its point measurement QPE accuracy

Study of water vapor vertical variability and possible cloud formation with a small network of GPS stations

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Radar interferometry technique: 3-D wind measurement theory

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Influence of the wind profile on the initiation of convection in mountainous terrain

International audienceA number of days with small precipitating convective cells were investigated using weather radars during the COPS (Convective and Orographically-induced Precipitation Study) field campaign in the region of the Vosges and the Rhine Valley in Central Europe. Depending on the weather situation, two distinct mechanisms could be identified for the initiation of convection. On some days, cells were initiated over the ridge of the Vosges, whereas on other days cells were initiated in the lee of the Vosges. The initiation of convection appeared to be concentrated in a few favourable locations. Using the Froude number, it was possible to describe the two distinct mechanisms. When the Froude number was low, the flow was diverted around the Vosges and thermally driven convergence at the ridge initiated convection, whereas when the Froude number was high, the flow passed through mountain gaps and then converged on the lee side with the flow in the Rhine Valley. The convergence on the lee side was enhanced at locations where the outflows through valleys converged. Low Froude numbers were accompanied by weak winds varying with height, whereas high Froude numbers were observed during situations with stronger southwesterly winds increasing with height

Investigation of the links between water vapor field evolution and rain rate based on 5 years of measurements at a midlatitude site

International audienceBased on 5 years of measurements of integrated water vapor (IWV), surface mixing ratio (MR), and rain rate, we investigate the relationship between the water vapor field evolution and the precipitation lifecycle. We show that in 76% of the cases the IWV reaches a maximum before the peak of precipitation, with the precipitation peak occurring on average 20 min after the IWV maximum. This delay can be related to the fall time of the precipitation. We also show that the moister the atmosphere, the greater the precipitation rates and the longer the delay. Unlike the IWV, the MR reaches a maximum after the precipitation peak in 60% of the cases, highlighting the interest of IWV compared to surface MR only. This paper and the discussions within it open a pathway to complementary studies and applications for heavy precipitation prediction

Histoire de radars

International audienceIn 1970, Henri Dessens, director of the Clermont-Fd Observatory, wanted to use radar to study the physics of the atmosphere. The idea became a reality with Serge Godard, who took over from Dessens at the head of the Observatory. He succeeded in recovering a military radar that was diverted from its original function to become a study and research instrument called ANATOL (ANAlyse et Trajectoire d'Orages Locaux). ANATOL's long career came to an end in 1995 after more than 45 years of good and loyal service in atmospheric research. However, the idea of using radars continued to grow and in 1993, under the direction of Daniel Ramon, an ST (Stratosphere-Troposphere) radar was installed with Météo-France. Then, in the mid-1990s, Jacques Kornprobst, director, launched the Observatory on the design and technical production of a prototype "volcanological" Doppler radar, VOLDORAD-1. Responding to volcanological needs, it was tested in a pioneering way at Etna in 1998. This success led to the construction of two other unique volcanological radars (VOLDORAD-2 and 2B) and a third (VOLDORAD-3). Since 2002, these radars have been combined into a dedicated observation service within the OPGC and are used for monitoring volcanic eruptions but also for atmospheric studies.En 1970, Henri Dessens, directeur de l'Observatoire de Clermont-Ferrand, souhaite utiliser des radars pour l'étude de la physique de l'atmosphère. L'idée se concrétise avec Serge Godard, qui prend la suite de Dessens à la tête de l'Observatoire. Il réussit à récupérer un radar militaire qui va être détourné de sa fonction première pour devenir un instrument d'étude et de recherche baptisé ANATOL (ANAlyse et Trajectoire d'Orages Locaux). La longue carrière d'ANATOL s'achève en 1995 après plus de 45 ans de bons et loyaux services dans la recherche atmosphérique. Mais l'idée d'utiliser des radars poursuit son chemin et dès 1993, sous la direction de Daniel Ramon, c'est l'installation d'un radar ST (Stratosphère-Troposphère) menée avec Météo-France. Puis, au milieu des années 1990, Jacques Kornprobst, directeur, lance l'Observatoire sur la conception et la réalisation technique d'un prototype de radar « volcanologique » à effet Doppler, VOLDORAD-1. Répondant à des besoins en volcanologie, il fut testé de façon pionnière sur le site de l’Etna en 1998. Ce succès conduisit dans la foulée à la construction de deux autres radars uniques en volcanologie (VOLDORAD-2 et 2B) puis d'un troisième (VOLDORAD-3). Réunis en un service d’observation dédié au sein de l’OPGC depuis 2002, ces radars sont utilisés pour la surveillance des éruptions volcaniques mais également pour des études atmosphériques