Spectroradiométrie du rayonnement solaire UV (mesures et analyses)

Le rayonnement solaire atteignant le sol a un impact important sur le monde du vivant (animal et végétal) ; ses effets sont d'autant plus importants que les photons incidents sont plus énergétiques (courtes longueurs d'onde). Le rayonnement UV solaire atteignant le sol ne représente environ que 5% du rayonnement solaire total mais à ces courtes longueurs d'onde, son efficacité biologique est importante. L'ozone, situé pour 90% dans la stratosphère entre 15 et 40 km d'altitude, constitue une véritable barrière du rayonnement. Une diminution de la quantité d'ozone stratosphérique est observée aux latitudes moyennes induisant une augmentation du rayonnement UV B. Divers réseaux de surveillance du rayonnement solaire UV B se mettent en place à travers le monde, avec pour but de mesurer cette évolution. L'ozone n'est pas le seul élément modulant la quantité d'UV B et par conséquent la puissance érythémale. L'altitude et l'enneigement ont aussi un rôle important. L'objectif de cette thèse est de créer deux stations de mesures automatisées du rayonnement UV et d'initier une analyse des paramètres qui influent sur ce rayonnement. Nous présentons les instruments utilisés et leurs caractéristiques techniques, et plus particulièrement celles du second spectroradiomètre développé au cours de cette thèse. Nous présentons également les méthodes et protocoles utilisés pour garantir la qualité des mesures. Après validation des instruments, nous avons débuté les mesures automatisées du rayonnement UV dans deux stations: la première à Villeneuve d'Ascq (59), et une seconde à Villard Saint Pancrace (05). A partir des mesures des éclairements spectriques UV, nous déterminons la colonne totale d'ozone. Par comparaison des mesures à des modèles d'éclairements, nous avons également évalué la réflectance d'un sol enneigé en milieu alpin. Cette thèse s'inscrit dans le cadre des projets européens SUVDAMA et CUVRALILLE1-BU (590092102) / SudocSudocFranceF

Variability of UV irradiance in Europe

The diurnal and annual variability of solar UV radiation in Europe is described for different latitudes, seasons and different biologic weighting functions. For the description of this variability under cloudless skies the widely used onedimensional version of the radiative transfer model UVSPEC is used. We reconfirm that the major factor influencing the diurnal and annual variability of UV irradiance is solar elevation. While ozone is a strong absorber of UV radiation its effect is relatively constant when compared with the temporal variability of clouds. We show the significant role that clouds play in modifying the UV climate by analyzing erythemal irradiance measurements from 28 stations in Europe in summer. On average, the daily erythemal dose under cloudless skies varies between 2.2 kJ m-2 at 70N and 5.2 kJ m-2 at 35N, whereas these values are reduced to 1.5–4.5 kJ m-2 if clouds are included. Thus clouds significantly reduce the monthly UV irradiation, with the smallest reductions, on average, at lower latitudes, which corresponds to the fact that it is often cloudless in the Mediterranean area in summer

A Climate Observatory in South West Indian Ocean: The Maïdo Observatory in La Réunion. Current achievements and Future Prospects

International audienceObservatories of the climate system are essential to assess future climate predictions that are central and fundamental requirements for determining future mitigation strategies. such observing platforms are very few ones in the tropical southern hemisphere. Cnrs, Université de la réunion, région réunion and the european FeDer program support together the construction of a high- altitude observatory which is operational since October 2012 in La Réunion (South West Indian Ocean, 2160 m asl, latitude 21°S, longitude 55°E). The Maïdo observatory takes over from its predecessor programs at sea level over the island who started long-term observation data of atmospheric chemical composition since 1994. the Maïdo observatory is an ideal platform to sample the atmosphere with different techniques (in-situ analysers, radiosounding, passive and active remote sensing) and to record surface measurements and vertical profiles from ground to the mesosphere over a subtropical latitude band poorly sampled by other international programs. The Maïdo observatory hosts lidars, one UV spectrometer, one radiosonding station, Ftir spectrometers, microwave radiometers, one lightning antenna, cameras, one Gnss station, microbarometers, etc. these devices sample many atmospheric parameters (e.g., meteorological parameters, reactive and greenhouse gases, aerosols, lightning and transient luminous events, infrasounds, etc). part of this very extensive range of instruments is approved and belongs to international networks like nDaCC (network for the Detection of atmospheric Composition Change), sHaDOZ (southern Hemisphere aDditional OZonesondes), tCCOn (total Carbon Column Observing network), and WWLLN (World Wide Lightning Location Network). in-situ analysers regroup measurements of reactive and greenhouse gases, and aerosols measurements approved by or applying to networks like GAW/WMO (Global Atmospheric Watching / World Meteorological Organization), iCOs (integrated Carbon Observing system). The Maïdo observatory is currently the only way to provide regular remote and in-situ atmospheric observations at subtropical latitudes and at high resolutions (seconds in time, few tenths of meters vertically) over a marine-remote region poorly sampled by other programs. it provides data for users in science and policy including air quality forecasting, verification of CO2 emissions and Kyoto monitoring, numerical weather prediction, and validation of global chemical transport model, global climate chemical model and satellite products. since its participation in on-going european projects (nOrs, aCtris-2, arise-2), and thanks to the start of delivery of data in near real time, the Maïdo observatory will largely contribute to the Copernicus atmosphere Monitoring services (CaMs). the Maïdo observatory is open to transnational access thanks to its participation in european programmes like aCtris-2 and enVriplus. this presentation will give an overview of results achieved so far and a number of highlights to illustrate the promise Maïdo observatory data hold for the future, allowing new applications and analysis for a broad community of users

Ozone column retrieval from solar UV measurements at ground level: Effects of clouds and results from six European sites

A differential absorption method, developed by the Laboratoire d'Optique Atmospherique (LOA), is applied to retrieve the total ozone column from UV global irradiance spectra under clear and cloudy sky conditions. Contrarily to clear sky, cloudy sky generates a high uncertainty in the retrieved ozone column. This study shows that under cloudy conditions the daily ozone mean is a rather good estimation of the true value. The standard deviation allows us to estimate the relative uncertainty of this mean value, i.e., about 7%. Results for all conditions from 3 years at Villeneuve d'Ascq are presented, as well as a comparison with TOMS (Total Ozone Mapping Spectrometer) data. The results are very similar to those obtained for clear days: In 75% of cases both values agree to within 5%; however, some cases present larger relative differences. Over the 3 years considered, there is a bias less than 3% (LOA>TOMS). This method is applied to five other European sites involved in the EDUCE (European Database for UV Climatology and Evaluation) project. Three of them are Brewer stations. The results of the comparison between the LOA-retrieved ozone and TOMS data show that a relative difference smaller than 5% is obtained in 63-80% of the cases, depending on site and year. Biases smaller than 3% are observed (LOA>TOMS). The comparison between the LOA-retrieved ozone and total ozone data from direct sun and zenith sky observations of the Brewer instruments shows better agreement. For more than about 80% of cases, except at one site, the relative difference is smaller than 5%, and the biases are smaller than 1%. The LOA method allows us to obtain a complementary data set and hence to provide time series of reliable measurements of total ozone column under all sky conditions

L'Observatoire de Physique de l'Atmosphère de la Réunion

National audienceCommunication about L'Observatoire de Physique de l'Atmosphère de la Réunio

Soil carbon,multiple benefits

In March 2013,40 leading experts from across the world gathered at a workshop, hosted by the EuropeanCommission, Directorate General Joint Research Centre, Italy, to discuss the multiple benefits o fsoil carbon as part of a Rapid Assessment Process (RAP) project commissioned by Scientific Committee on Problems of the Environment (SCOPE). This collaboration led to the publication of the SCOPE Series Volume 71 “Soil Carbon:Science, Management and Policy for Multiple Benefits”; which brings together the essential scientific evidence and policy opportunities regarding the global importance of soil carbon.This short communication summarizes the key messages of the assessment including research and policy implications. & 2014ElsevierLtd.JRC.H.5-Land Resources Managemen