462 research outputs found
Remote sensing of cirrus clouds and aerosols by a sun photometer in Tunisia
International audienceSome ground based measurements of solar radiation by using a sun photometer, have been conducted in Tunisia during the period of November 2000âFebruary 2002. Five key measurement sites were selected: Three Sites (Tunis, Sousse, Gabes) are located on the Mediterranean coast and Two sites (Gafsa, Tozeur) on the boarder of Sahara. Over a total of 149 measurement days, 21 days are identified as clear sky, 114 days as Cirrus clouds and 14 days as aerosols. Aerosols and Cirrus clouds Optical Thickness (AOT) are derived from photometric measurements at 532 nm wavelength. Spatial and temporal variabilities of AOT are presented and discussed in this paper. Cirrus clouds were frequently observed at Gafsa and Tozeur where saharan aerosol events are expected to be more frequent than cirrus clouds. The mediterranean sea and saharan aerosols are suspected to have the main role in cirrus clouds formation, by providing water vapor and high concentrations of cloud condensation and ice forming nuclei
Lagrangian dust model simulations for a case of moist convective dust emission and transport in the western Sahara region during Fennec/LADUNEX
Due to the harshness and inaccessibility of desert regions, the uncertainties concerning the processes of dust mobilization at the surface, airborne transport, and sedimentation are still considerable, limiting the ability to perform model simulations. In June 2011, a comprehensive data set of ground-based and airborne in situ measurements and remote sensing observations was acquired within the Fennec/Lagrangian Dust Source Inversion Experiment (LADUNEX) field campaign in the western Sahara region. Here we evaluate the ability of the state-of-the-art Lagrangian particle dispersion model FLEXPART, newly fitted with a dust mobilization capability, to simulate dust transport in this region. We investigate a case where a large mesoscale convective system (MCS) triggered dust emissions in central Mali, which subsequently moved as a large cold pool dust front toward northern Mauritania. Specifying dust mobilization for this case is shown to be an important obstacle to simulating dust transport during this event, since neither the MCS nor the associated cold pool-causing dust emission is represented in the meteorological analysis. Obtaining a realistic dust transport simulation for this case therefore requires an inversion approach using a manual specification of the dust sources supported by satellite imagery. When compared to in situ and remote sensing data from two aircraft, the Lagrangian dust transport simulations represent the overall shape and evolution of the dust plume well. While accumulation and coarse mode dust are well represented in the simulation, giant mode particles are considerably underestimated. Our results re-emphasize that dust emission associated with deep moist convection remains a key issue for reliable dust model simulations in northern Africa
Estimation des paramÚtres génétiques de la vitesse de croissance et du poids des agneaux avant le sevrage en race mérinos d'arles
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Is periventricular heterotopia a useful endpoint for developmental thyroid hormone system disruption in mouse toxicity studies?
Data availability: Data will be made available on request.In rats, hypothyroidism during fetal and neonatal development can disrupt neuronal migration and induce the formation of periventricular heterotopia in the brain. However, it remains uncertain if heterotopia also manifest in mice after developmental hypothyroidism and whether they could be used as a toxicological endpoint to detect TH-mediated effects caused by TH system disrupting chemicals. Here, we performed a mouse study where we induced severe hypothyroidism by exposing pregnant mice (n = 3) to a very high dose of propylthiouracil (PTU) (1500 ppm) in the diet. This, to obtain best chances of detecting heterotopia. We found what appears to be very small heterotopia in 4 out of the 8 PTU-exposed pups. Although the incidence rate could suggest some utility for this endpoint, the small size of the ectopic neuronal clusters at maximum hypothyroidism excludes the utility of heterotopia in mouse toxicity studies aimed to detect TH system disrupting chemicals. On the other hand, parvalbumin expression was manifestly lower in the cortex of hypothyroid mouse offspring demonstrating that offspring TH-deficiency caused an effect on the developing brain. Based on overall results, we conclude that heterotopia formation in mice is not a useful toxicological endpoint for examining TH-mediated developmental neurotoxicity.EU Horizon 2020 programme to two projects: grant number 825161 for the project âATHENA: Assays for the identification of Thyroid Hormone axis-disrupting chemicals: Elaborating Novel Assessment strategiesâ (Kortenkamp et al., 2020), and grant number 825753 for the project âERGO: Breaking Down the Wall Between Human Health and Environmental Testing of Endocrine Disruptorsâ (Holbech et al., 2020) as well as the Danish Environmental Protection Agency, Ministry of Environment of Denmark
Impact of upstream moisture structure on a back-building convective precipitation system in south-eastern France during HyMeX IOP13
The present study examines the impact of the environmental moisture structure
in the lower troposphere (below 2 km above sea level, a.s.l.) on the
precipitation development, observed in southern France during Intensive
Observation Period (IOP) 13 of the first Special Observation Period of the
Hydrological cycle in the Mediterranean Experiment (HyMeX SOP-1), through a
series of sensitivity experiments using the non-hydrostatic mesoscale
atmospheric numerical model (Meso-NH). The control simulation (CNTL) and all
the other 12 sensitivity experiments examined in this study succeed in
reproducing a heavy precipitation event (HPE) in the coastal mountainous
region of Var in south-eastern France as observed. The sensitivity
experiments are designed to investigate the response of the HPE to the
variability of the water vapour content upstream in the moist marine
atmospheric boundary layer (MABL) and the drier air above. The comparisons
between CNTL and the 12 sensitivity experiments show how the life cycle of
precipitation associated with the HPE, but also the upstream flow (over the
sea), is modified, even for moisture content changes of only 1 g kgâ1
below 2 km a.s.l. Within the low-level wind convergence between southerlies
and south-westerlies, a small increase of moisture content in the MABL
prolongs moderate precipitation (â„5 mm in 15 min) and enlarges the
area of weak precipitation (â„1 mm in 15 min). The moistening in the
1â2 km a.s.l. layer, just above the MABL, prolongs the duration of
moderate precipitation, for a similar total precipitation amount as in CNTL.
The drier MABL and 1â2 km a.s.l. layer shorten the lifetime of
precipitation and reduce the total precipitation amount with respect to CNTL.
We also found that the moisture in the MABL has a stronger impact on
producing enhanced precipitation (both in terms of amount and intensity) than
the moisture just above (1â2 km a.s.l.). Also, it is worth noting that
adding moisture in the MABL does not necessarily lead to enhanced
precipitation amount. In moistening the MABL, the duration of moderate
precipitation increases with increasing moisture as does the area covered by
weak precipitation, while the area covered by the intense precipitation (â„30 mm) decreases. Despite a simplified moisture-profile modification
approach, this study suggests that moisture structure in the lower
troposphere is key for accurate prediction at short-term range of the timing
and location of precipitation in the coastal mountainous region in southern
France.</p
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