Weather regimes and related atmospheric composition at a Pyrenean observatory characterized by hierarchical clustering of a 5-year data set

Atmospheric composition measurements taken at many high-altitude stations around the world, aim to collect data representative of the free troposphere and of an intercontinental scale. However, the high-altitude environment favours vertical mixing and the transportation of air masses at local or regional scales, which has a potential influence on the composition of the sampled air masses. Mixing processes, source-receptor pathways, and atmospheric chemistry may strongly depend on local and regional weather regimes, and these should be characterized specifically for each station. The Pic du Midi (PDM) isa mountaintop observatory (2850 m a.s.l.) on the north side of the Pyrenees. PDM is associated with the Centre de Recherches Atmosph{\'e}riques (CRA), a site in the foothills ar 600 m a.s.l. 28 km north-east of the PDM. The two centers make up the Pyrenean Platform for the Observation of the Atmosphere (P2OA). Data measured at PDM and CRA were combined to form a5-year hourly dataset of 23 meteorological variables notably: temperature, humidity, cloud cover, wind at several altitudes. The dataset was classified using hierarchical clustering, with the aim of grouping together the days which had similar meteorological characteristics. To complete the clustering, we computed several diagnostic tools, in order to provide additional information and study specific phenomena (foehn, precipitation, atmospheric vertical structure, and thermally driven circulations). This classification resulted in six clusters: three highly populated clusters which correspond to the most frequent meteorological conditions (fair weather, mixed weather and disturbed weather, respectively); a small cluster evidencing clear characteristics of winter northwesterly windstorms; and two small clusters characteristic of south foehn (south- to southwesterly large-scaleflow, associated with warm and dry downslope flow on the lee side of the chain). The diagnostic tools applied to the six clusters provided results in line with the conclusions tentatively drawn from 23 meteorological variables. This, to some extent,validates the approach of hierarchical clustering of local data to distinguish weather regimes. Then statistics of atmospheric composition at PDM were analysed and discussed for each cluster. Radon measurements, notably, revealed that the regional background in the lower troposphere dominates the influence of diurnal thermal flows when daily averaged concentrations are considered. Differences between clusters were demonstrated by the anomalies of CO, CO$_2$, CH$_4$, O$_3$ and aerosol number concentration, and interpretations in relation with chemical sinks and sources are proposed.Comment: Atmospheric Chemistry and Physics, In pres

Cellular and Behavioral Effects of Cranial Irradiation of the Subventricular Zone in Adult Mice

Background: In mammals, new neurons are added to the olfactory bulb (OB) throughout life. Most of these new neurons, granule and periglomerular cells originate from the subventricular zone (SVZ) lining the lateral ventricles and migrate via the rostral migratory stream toward the OB. Thousands of new neurons appear each day, but the function of this ongoing neurogenesis remains unclear. Methodology/Principal Findings: In this study, we irradiated adult mice to impair constitutive OB neurogenesis, and explored the functional impacts of this irradiation on the sense of smell. We found that focal irradiation of the SVZ greatly decreased the rate of production of new OB neurons, leaving other brain areas intact. This effect persisted for up to seven months after exposure to 15 Gray. Despite this robust impairment, the thresholds for detecting pure odorant molecules and short-term olfactory memory were not affected by irradiation. Similarly, the ability to distinguish between odorant molecules and the odorant-guided social behavior of irradiated mice were not affected by the decrease in the number of new neurons. Only long-term olfactory memory was found to be sensitive to SVZ irradiation. Conclusion/Significance: These findings suggest that the continuous production of adult-generated neurons is involved i

Widespread pesticide distribution in the European atmosphere questions their degradability in air

Risk assessment of pesticide impacts on remote ecosystems makes use of model-estimated degradation in air. Recent studies suggest these degradation rates to be overestimated, questioning current pesticide regulation. Here, we investigated the concentrations of 76 pesticides in Europe at 29 rural, coastal, mountain, and polar sites during the agricultural application season. Overall, 58 pesticides were observed in the European atmosphere. Low spatial variation of 7 pesticides suggests continental-scale atmospheric dispersal. Based on concentrations in free tropospheric air and at Arctic sites, 22 pesticides were identified to be prone to long-range atmospheric transport, which included 15 substances approved for agricultural use in Europe and 7 banned ones. Comparison between concentrations at remote sites and those found at pesticide source areas suggests long atmospheric lifetimes of atrazine, cyprodinil, spiroxamine, tebuconazole, terbuthylazine, and thiacloprid. In general, our findings suggest that atmospheric transport and persistence of pesticides have been underestimated and that their risk assessment needs to be improved

Widespread pesticide distribution in the European atmosphere questions their degradability in air

Risk assessment of pesticide impacts on remote ecosystems makes use of model-estimated degradation in air. Recent studies suggest these degradation rates to be overestimated, questioning current pesticide regulation. Here, we investigated the concentrations of 76 pesticides in Europe at 29 rural, coastal, mountain, and polar sites during the agricultural application season. Overall, 58 pesticides were observed in the European atmosphere. Low spatial variation of 7 pesticides suggests continental-scale atmospheric dispersal. Based on concentrations in free tropospheric air and at Arctic sites, 22 pesticides were identified to be prone to long-range atmospheric transport, which included 15 substances approved for agricultural use in Europe and 7 banned ones. Comparison between concentrations at remote sites and those found at pesticide source areas suggests long atmospheric lifetimes of atrazine, cyprodinil, spiroxamine, tebuconazole, terbuthylazine, and thiacloprid. In general, our findings suggest that atmospheric transport and persistence of pesticides have been underestimated and that their risk assessment needs to be improved

Ozone Photochemical Production Rates in the Western Mediterranean

International audienc

Analyses eulériennes et lagrangiennes des systèmes convectifs quasi-stationnaires sur les Alpes

This thesis is related to the scientific objective "Orographic precipitation mechanisms" of MAP (Mesoscale Alpine Programme) and investigates how the precipitation is triggered and enhanced over mountain slopes exposed to quasi-stationary humid air-flows. The problem of the numerical forecast of heavy rain at the scale of few kilometers is also tackled. Most heavy-precipitation events in autumn over the Alps are characterized by a quasi-stationary southerly or south-westerly flow advecting maritime air from the Mediterranean towards the Alpine ridge. The case of MAP IOP (Intensive Observation Period) 2B is modelled with the numerical simulation system MesoNH. An original Lagrangian analysis method enables to identify a dry air-mass at the scale meso-beta over the Mediterranean and to study its evolution and influence on the rain distribution over the Alps. The heavy precipitation over the southern slopes of the Alps is studied with idealised numerical simulations, where the southerly or south-westerly upstream flow is prescribed as uniform and stationary. The obtained rain distributions are in agreement with the climatological analysis. This indicates that the maximum areas correspond to regions of enhanced orographic lifting of the incident flow. Further simulations at high-resolution and with a purely resolved cloud physics allow to characterize triggering and development mechanisms which are specific for the south side of the Alps. Some were observed during MAP. They appear as very complex, even in the simulations despite the simplification of the upstream flow.La thèse s'inscrit dans le thème "Mécanismes des précipitations orographiques" de MAP (Mesoscale Alpine Programme). Elle étudie le déclenchement et l'intensification des précipitations sur un relief exposé à un flux humide quasi-stationnaire, et examine le problème de la prévision numérique des fortes précipitations à l'échelle de quelques kilomètres. Un flux de sud à sud-ouest quasi-stationnaire caractérise la plupart des épisodes de pluies diluviennes sur les Alpes à l'automne, où de l'air méditerranéen est advecté vers le relief. Le cas de la POI (Période d'Observation Intensive) 2B de MAP est simulé avec le modèle MesoNH. Une méthode d'analyse lagrangiennne originale permet d'identifier une masse d'air sec d'échelle méso-béta sur la Méditerranée, et d'étudier son évolution et son influence sur la répartition des précipitations sur les Alpes. Les fortes précipitations sur les versants sud des Alpes sont étudiées grâce à des simulations idéalisées, où l'écoulement incident de sud ou sud-ouest est rendu uniforme et stationnaire. Les distributions obtenues, proches des données climatologiques, indiquent que les zones les plus arrosées correspondent à un forçage orographique du flux incident plus prononcé. Enfin, ces simulations permettent, à haute résolution et avec une microphysique explicite, l'identification de mécanismes de déclenchement et de développement de la convection spécifiques à la région sud-alpine - dont certains ont pu être observés pendant MAP. Ils se révèlent très complexes malgré la simplification des conditions en amont

Analyses eulériennes et lagrangiennes des systèmes convectifs quasi-stationnaires sur les Alpes

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Autumnal precipitation distribution on the southern flank of the Alps: A numerical-model study of the mechanisms

During the autumn there are frequent events of heavy precipitation on the southern slopes of the meso-α-scale Alpine chain. Moreover, the accompanying climatology exhibits a distinctive spatial distribution with some meso-β-scale regions of enhanced precipitation such as the ‘wet spot’ in the vicinity of Lago Maggiore.Possible mechanisms to account for the observed spatial distribution are established using a heuristic model-based approach. It is shown using a mesoscale model that the response to a steady, horizontally uniform, and moisture-laden flow impinging upon a comparatively realistic representation of the Alpine chain can reproduce both the overall meso-α-scale precipitation distribution and its meso-β-scale sub-structure. The nature of the simulated flow regime (over, around or intermediate) is sensitive to the strength of the ambient geostrophic flow and its modification in the planetary boundary layer. Contrariwise, the simulated precipitation distribution in the Lago Maggiore ‘wet spot’ is comparatively insensitive to the changes in direction of the incident geostrophic flow from south to south-west, and in strength in the range 10–30 m s−1, although there is a marked change in the structure of the near-Alpine flow. This systematic precipitation enhancement appears to be related to the relative strength and compensating effects of an easterly barrier jet tracking along the zonally elongated part of the Alps and an air stream channelled between the Maritime Alps and the Apennines.Further evidence to the above interpretation of the meso-β-scale precipitation distribution is given with simulations conducted using a smoothed and schematic representation of the Alpine chain. Likewise, the sensitivity to the presence of a Lago Maggiore-like indentation of the topography is tested, and evidence is provided of a further ‘indentation-induced’ precipitation enhancement at the local scale

Autumnal precipitation distribution on the southern flank of the Alps: A numerical-model study of the mechanisms

During the autumn there are frequent events of heavy precipitation on the southern slopes of the meso-α-scale Alpine chain. Moreover, the accompanying climatology exhibits a distinctive spatial distribution with some meso-β-scale regions of enhanced precipitation such as the ‘wet spot’ in the vicinity of Lago Maggiore.Possible mechanisms to account for the observed spatial distribution are established using a heuristic model-based approach. It is shown using a mesoscale model that the response to a steady, horizontally uniform, and moisture-laden flow impinging upon a comparatively realistic representation of the Alpine chain can reproduce both the overall meso-α-scale precipitation distribution and its meso-β-scale sub-structure. The nature of the simulated flow regime (over, around or intermediate) is sensitive to the strength of the ambient geostrophic flow and its modification in the planetary boundary layer. Contrariwise, the simulated precipitation distribution in the Lago Maggiore ‘wet spot’ is comparatively insensitive to the changes in direction of the incident geostrophic flow from south to south-west, and in strength in the range 10–30 m s−1, although there is a marked change in the structure of the near-Alpine flow. This systematic precipitation enhancement appears to be related to the relative strength and compensating effects of an easterly barrier jet tracking along the zonally elongated part of the Alps and an air stream channelled between the Maritime Alps and the Apennines.Further evidence to the above interpretation of the meso-β-scale precipitation distribution is given with simulations conducted using a smoothed and schematic representation of the Alpine chain. Likewise, the sensitivity to the presence of a Lago Maggiore-like indentation of the topography is tested, and evidence is provided of a further ‘indentation-induced’ precipitation enhancement at the local scale