As a first step towards coupling atmospheric and hydrological models, this article describes the implementation of the Interface Soil Biosphere Atmosphere (ISBA) surface scheme within a macroscale ...hydrological model at the regional scale. The introduction of the diurnal cycle in the hydrological model allows a coupling with the atmosphere through the energy balance and water budget computations. The coupled model is used in a forced mode, i.e. atmospheric forcing is imposed on the surface scheme without any retroaction of the surface exchanges on the atmosphere. The initial version of ISBA was modified to account for sub-grid runoff. Existing classifications of soil and vegetation at high spatial resolution (1
km) were used in conjunction with satellite information to monitor the monthly evolution of the vegetation. A dense surface network facilitated the interpolation of atmospheric fields with a time step of 3
h. The two years considered show large differences of annual precipitation and potential evaporation, which have an impact on the regime of the river flows. A one-dimensional study presents the sensitivity of the partitioning of precipitation into evaporation and runoff to the sub-grid runoff and drainage parameterizations, soil depth, and vegetation cover.
Les modèles météorologiques qui travaillent à méso-échelle intègrent de nouveaux schémas de surface qui ont été spécialement conçus pour simuler le comportement des villes. Ces schémas les rendent en ...principe aptes à simuler spécifiquement les contraintes qu’exerce la ville sur les basses couches de l’atmosphère. Lorsqu’ils sont activés, ils permettent d’étudier le comportement de la couche limite urbaine ou les interactions qui existent entre la ville et la campagne. Cependant, avant d’accorder une confiance aveugle à ces modèles, il est indispensable d’en vérifier les aptitudes. C’est pourquoi, dans un premier temps, il est nécessaire de faire la simulation d’un cas réel pour lequel on dispose de données observées servant à valider la simulation. L’objectif de cet article consiste à présenter un certain nombre d’analyses qui ont été réalisées à partir d’une simulation dont les résultats ont été validés et vérifiés par une confrontation avec des données de terrain. Cette simulation concerne l’agglomération de Strasbourg (450 000 habitants) et a pour objectif d’en reproduire l’îlot de chaleur urbain. Elle a été effectuée à l’aide de la version standard du modèle Méso-NH, qui est un modèle qui appartient conjointement à Météo-France et au Laboratoire d’Aérologie de l’Université Paul Sabatier de Toulouse. La simulation a été réalisée pour des journées anticycloniques d’été pour lesquelles les conditions météorologiques sont favorables à l’apparition du phénomène : à savoir un ensoleillement maximum et des vitesses de vent faibles. La simulation se prolonge sur 5 jours, du 13 au 17 août 2002. Le 13 août est encore un peu perturbé et est marqué par des passages nuageux. C’est une journée d’initialisation et de mise à l’équilibre des champs du modèle. La procédure de simulation consiste à initialiser les champs du modèle et à les contraindre périodiquement aux limites (toutes les 6h) grâce aux réanalyses du centre de prévision européen (CEPMMT), et ceci afin d’en limiter la dérive. La qualité de la simulation a été vérifiée à l’aide de données qui ont été acquises en 2002 lors d’une campagne de mesures réalisée dans le cadre d’un projet de recherche appelé Rayonnement Energie dans la Couche Limite Urbaine à Strasbourg (RECLUS). Les résultats ont été comparés aux mesures pour un certain nombre de variables fondamentales et dans l’ensemble, force est de constater que pour la plupart des paramètres analysés, les résultats obtenus sont très cohérents. Par conséquent, il est possible de se baser sur cette simulation pour réaliser des investigations que ne permettent pas (ou difficilement) les réseaux de mesures (comme par exemple l’obtention d’informations spatialisées). Après une journée de simulation, lorsque le beau temps s’installe vraiment (
i.e.
le 14 août), l’îlot de chaleur apparaît systématiquement les nuits sur Strasbourg. La simulation est alors utilisée pour réaliser une analyse fine des processus et de leurs conséquences sur l’atmosphère urbaine. En conclusion, cette étude confirme l’utilité de ces modélisations du climat urbain qui sont maintenant suffisamment fiables pour devenir indispensables en recherche fondamentale (pour mettre en évidence les mécanismes), mais aussi en recherche appliquée (dans la perspective de l’aménagement urbain).
The mesoscale meteorological models include new surface schemes that have been design to simulate the urban behaviour. These schemes made them able to simulate the constraint exerted by the town on the low level layers of the atmosphere. When they are activated, they allow to study the behaviour of the urban boundary layer dynamics or the interaction that exists between the town and the rural areas. But, all these models have their own weaknesses and it is necessary to verify the quality of their results. It is the reason why, in a first step, it is necessary to do a simulation on a real case, for which validation data are available. The aim of this paper is to present a simulation of the urban heat island at Strasbourg (450 000 inhabitants). The simulation is done with the Méso-NH model of Météo-France and the Laboratoire d’Aérologie of the Paul Sabatier University (Toulouse). It is done for anticyclonic summer days for which the weather conditions permits the development of the phenomenon (low winds and maximum incoming radiation). The simulation extends on 5 days (from august 13 to 17, 2002). The first day (august 13) was still concerned by some clouds and is considered as an initialisation day. The simulation procedure consists to initialise the meteorological fields and to constrain them every 6 hours with the reanalysis of the European Prevision Centre (CEPMMT). The quality of the simulation was verified with data acquired during a measurement campaign that took place in 2002 in the frame of a research project called (RECLUS). The simulation results were compared to the measurements for some fundamental variables. On the whole, the results are satisfactory. Consequently, it is possible to use the simulation to investigate the urban climate better than with the measurements alone (especially with regard to the spatial information). After one simulation day, when the weather conditions become ideal (the august 14), the urban heat island is fully developed during all the nights. The simulation can be used to do an analysis of the processes and their consequences on the urban atmosphere. As a conclusion, this study confirms the usefulness to obtain realistic simulations of the urban climate. The results are helpful in fundamental research (to understand the mechanisms) and also in the field of the applied research (especially for the need of urban planning).
The CarboEurope Regional Experiment Strategy (CERES) experiment took place in May and June 2005 in France and offers a comprehensive database on atmospheric CO sub(2) and boundary layer processes at ...the regional scale. One golden day of CERES is interpreted with the mesoscale atmospheric model Meso-NH coupled on-line with the Interactions between Soil, Biosphere and Atmosphere, CO sub(2)-reactive (ISBA-A-gs) surface scheme, allowing a full interaction of CO sub(2) between the surface and the atmosphere. The rapid diurnal cycle of carbon coupled with water and energy fluxes is parameterized including, e.g., plant assimilation, respiration, anthropogenic emissions, and sea fluxes. During the analyzed day, frequent vertical profiles and aircraft transects revealed high spatial and temporal variabilities of CO sub(2) concentrations within the boundary layer at the regional scale: a 10- ppm gradient of CO sub(2)-mixing ratio is observed during the day by the aircraft measurements. The Meso-NH model proved able to simulate very well the CO sub(2) concentration variability as well as the spatial and temporal evolution of the surface fluxes and the boundary layer in the domain. The model is used to explain the CO sub(2) variability as a result of two complementary processes: (1) the regional heterogeneity of CO sub(2) surface fluxes related to the land cover (e.g., winter crops versus a pine forest) and (2) the variability of mesoscale circulation across the boundary layer: development of the sea breeze in the western part of the domain and dominating wind flow in the eastern part of the domain.
A macroscale hydrological model including an improved representation of the surface processes is validated at a regional scale using the data set collected during the Hapex-Mobilhy experiment (1986). ...Using observed atmospheric forcing with a resolution of 5
km and realistic fields of vegetation and soil types in a large area, the hydrological model correctly simulates daily streamflows for two contrasting climatological years in 1986 and 1987, provided that a sub-grid scale parameterization of surface runoff is included in the surface scheme. The comparison with point observations of evaporation and soil water content shows that the surface scheme satisfactorily reproduces the annual water budget for very diverse land uses. It is shown that, although the annual rainfall was significantly lower in 1987, the annual evaporation was higher than in 1986 because precipitation fell mainly in summer. The reduction of precipitation contributed to a comparable reduction of total runoff, and therefore a drastic decrease in the river flows as confirmed by the observations. The second part of the study addresses the issue of modelling the surface water budget at a large grid scale. Once validated, the macroscale hydrological model is used as a reference to test aggregation methods. Aggregated fluxes of evaporation, drainage and surface runoff are found to be close to the reference fluxes provided that sub-grid scale surface runoff and interception losses are taken into account in the aggregation procedure.
To provide an accurate water budget over a whole basin, hydrological models need to know the spatial variability of evapotranspiration at the watershed scale. The three-dimensional (3D) atmospheric ...models can provide such estimations at a regional scale, since they calculate the different energy and water fluxes by accounting for the landscape heterogeneity with a mesh grid varying from a few metres to several kilometres. We have used such a transfer model (Meso-NH) at a high spatial scale (50 m) to simulate the small agricultural region of the Alpilles (4 km × 5 km), where an experiment took place in 1997 and included intense ground measurements on different types of crops and airborne and satellite data collection. It was the first time that this model was used at such a fine resolution. The aim of this paper is to analyze the effects of the various crops on the spatial variability of the main energy fluxes, particularly evapotranspiration. We also wished to validate Meso-NH from this important available dataset. All input parameters were derived from remote sensing or airborne data: leaf area index (LAI) and albedo were computed from polarization and directionality of the earth's reflectances (POLDER) images. Roughness length was estimated combining both a land-use map obtained from Satellite pour l'Observation de la Terre (SPOT) images and the POLDER images. Maps of the main energy fluxes and temperatures were simulated for two periods in April and June and showed large spatial variations because of differences in soil moisture and in roughness of the crop types. Comparisons between the simulations and the measurements gave satisfactory results. Thermal images acquired by the infrared airborne camera were in good agreement with the surface temperatures estimated by the model. Significant differences were observed when we compared, on the same area, the value of averaged fluxes with the value of fluxes calculated with averaged surface parameters. This was due to the nonlinearity processes associated with averaging of environmental variables. The interest in using a mesoscale model applied at microscale is that coherent structures can be observed in the surface boundary layer, particularly on transects of the vertical wind speed. Such structures cannot be simulated at a larger scale or analyzed with simplified models. Remote sensing data acquired at a fine spatial resolution are a useful tool to provide accurate surface parameters to such a model. This allows quantification of the effect of each crop type on the spatial variation of temperature and evapotranspiration and thus improves our knowledge of the water budget of an agricultural landscape and the watershed functioning.
We update our previous search for trapped magnetic monopoles in LHC Run 2 using nearly six times more integrated luminosity and including additional models for the interpretation of the data. The ...MoEDAL forward trapping detector, comprising 222 kg of aluminium samples, was exposed to 2.11 fb−1 of 13 TeV proton–proton collisions near the LHCb interaction point and analysed by searching for induced persistent currents after passage through a superconducting magnetometer. Magnetic charges equal to the Dirac charge or above are excluded in all samples. The results are interpreted in Drell–Yan production models for monopoles with spins 0, 1/2 and 1: in addition to standard point-like couplings, we also consider couplings with momentum-dependent form factors. The search provides the best current laboratory constraints for monopoles with magnetic charges ranging from two to five times the Dirac charge.
A macroscale hydrological model including an improved representation of the surface processes is validated at a regional scale using the data set collected during the Hapex-Mobilhy experiment (1986). ...Using observed atmospheric forcing with a resolution of 5 km and realistic fields of vegetation and soil types in a large area, the hydrological model correctly simulates daily streamflows for two contrasting climatological years in 1986 and 1987, provided that a sub-grid scale parameterization of surface runoff is included in the surface scheme. The comparison with point observations of evaporation and soil water content shows that the surface scheme satisfactorily reproduces the annual water budget for very diverse land uses. It is shown that, although the annual rainfall was significantly lower in 1987, the annual evaporation was higher than in 1986 because precipitation fell mainly in summer. The reduction of precipitation contributed to a comparable reduction of total runoff, and therefore a drastic decrease in the river flows as confirmed by the observations. The second part of the study addresses the issue of modelling the surface water budget at a large grid scale. Once validated, the macroscale hydrological model is used as a reference to test aggregation methods. Aggregated fluxes of evaporation, drainage and surface runoff are found to be close to the reference fluxes provided that sub-grid scale surface runoff and interception losses are taken into account in the aggregation procedure.
As a first step towards coupling atmospheric and hydrological models, this article describes the implementation of the Interface Soil Biosphere Atmosphere (ISBA) surface scheme within a macroscale ...hydrological model at the regional scale. The introduction of the diurnal cycle in the hydrological model allows a coupling with the atmosphere through the energy balance and water budget computations. The coupled model is used in a forced mode, i.e. atmospheric forcing is imposed on the surface scheme without any retroaction of the surface exchanges on the atmosphere. The initial version of ISBA was modified to account for sub-grid runoff. Existing classifications of soil and vegetation at high spatial resolution (1 km) were used in conjunction with satellite information to monitor the monthly evolution of the vegetation. A dense surface network facilitated the interpolation of atmospheric fields with a time step of 3 h. The two years considered show large differences of annual precipitation and potential evaporation, which have an impact on the regime of the river flows. A one-dimensional study presents the sensitivity of the partitioning of precipitation into evaporation and runoff to the sub-grid runoff and drainage parameterizations, soil depth, and vegetation cover.
The CarboEurope Regional Experiment Strategy (CERES) experiment took place in May and June 2005 in France and offers a comprehensive database on atmospheric CO
2
and boundary layer processes at the ...regional scale. One “golden” day of CERES is interpreted with the mesoscale atmospheric model Meso‐NH coupled on‐line with the Interactions between Soil, Biosphere and Atmosphere, CO
2
‐reactive (ISBA‐A‐gs) surface scheme, allowing a full interaction of CO
2
between the surface and the atmosphere. The rapid diurnal cycle of carbon coupled with water and energy fluxes is parameterized including, e.g., plant assimilation, respiration, anthropogenic emissions, and sea fluxes. During the analyzed day, frequent vertical profiles and aircraft transects revealed high spatial and temporal variabilities of CO
2
concentrations within the boundary layer at the regional scale: a 10‐ppm gradient of CO
2
‐mixing ratio is observed during the day by the aircraft measurements. The Meso‐NH model proved able to simulate very well the CO
2
concentration variability as well as the spatial and temporal evolution of the surface fluxes and the boundary layer in the domain. The model is used to explain the CO
2
variability as a result of two complementary processes: (1) the regional heterogeneity of CO
2
surface fluxes related to the land cover (e.g., winter crops versus a pine forest) and (2) the variability of mesoscale circulation across the boundary layer: development of the sea breeze in the western part of the domain and dominating wind flow in the eastern part of the domain.
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