Papers by Bergametti Gilles
Relation between particulate concentration in the atmosphere and aerosol collection efficiency
Environmental Technology Letters
ABSTRACT
We present here a 3-year simulation (1990 to 1992) of the atmospheric cycle of Saharan dust over ... more We present here a 3-year simulation (1990 to 1992) of the atmospheric cycle of Saharan dust over the Atlantic with an off-line three-dimensional transport model. The results of the simulation have been compared with selected relevant measurements. Careful attention has been paid to the spatial and temporal consistency between the observations and the model results. Satellite observations of optical thickness and the model show a closely similar latitudinal shift and change of the aerosol plume extent from month to month over 3 years. This is explained by the dominant role of the large-scale transport, well described by the European Centre for Medium-Range Weather Forecasts winds, a sufficiently consistent description of aerosol physics along with a detailed prognostic source function. A feature not captured perfectly by the model is the winter maximum in observed optical depth, which is south of the satellite observation window. This underestimate in the very southern tropical region in winter suggests that additional aerosol sources become important, such as Sahelian dust and carbonaceous aerosols from biomass burning, not included in our simulation. However, spring and autumn simulated optical thickness is 50% less than that observed, while it is only 30% less in summer and winter. This is found for both the subtropical and the tropical Atlantic Ocean, which points to a general underestimate by the model, not just because of aerosol sources missing in the Sahel region. Another seasonal feature is discussed for Sal Island where measurements suggest that low-level dust transport in winter is replaced by a pronounced high-level Saharan dust layer in summer. The model reproduces this pattern except that there is also significant low level transport in summer, associated mainly with peculiar simulated dust transport events from the western Sahara. On a synoptic scale the frequency of dust outbreaks over the North Atlantic and of major dust deposition events in Spain and a dust vertical profile measured by a lidar over the Azores region are reproduced by the model. Long-term daily monitoring of Saharan dust load over marine areas using Meteosat ISCCP-B2 data, 1, Methodology and preliminary results for 1983-1994 in the western Mediterranean, J. Geophys. Res., 102, 16,947-16,958, 1997a. Moulin, C., F. Dulac, C. E. Lambert, P. Chazette, I. Jankowiak, B. Chatenet, and F. Lavenu, Long-term daily monitoring of Saharan dust load over marine areas using Meteosat ISCCP-B2 data, 2, Accuracy of the method and validation using Sun photometer measurements, J. Geophys. Res., 102, 16,959-16,969, 1997b.
Journal of Geophysical Research Atmospheres
We present here a 3-year simulation (1990 to 1992) of the atmospheric cycle of Saharan dust over ... more We present here a 3-year simulation (1990 to 1992) of the atmospheric cycle of Saharan dust over the Atlantic with an off-line three-dimensional transport model. The results of the simulation have been compared with selected relevant measurements. Careful attention has been paid to the spatial and temporal consistency between the observations and the model results. Satellite observations of optical thickness and the model show a closely similar latitudinal shift and change of the aerosol plume extent from month to month over 3 years. This is explained by the dominant role of the large-scale transport, well described by the European Centre for Medium-Range Weather Forecasts winds, a sufficiently consistent description of aerosol physics along with a detailed prognostic source function. A feature not captured perfectly by the model is the winter maximum in observed optical depth, which is south of the satellite observation window. This underestimate in the very southern tropical region in winter suggests that additional aerosol sources become important, such as Sahelian dust and carbonaceous aerosols from biomass burning, not included in our simulation. However, spring and autumn simulated optical thickness is 50% less than that observed, while it is only 30% less in summer and winter. This is found for both the subtropical and the tropical Atlantic Ocean, which points to a general underestimate by the model, not just because of aerosol sources missing in the Sahel region. Another seasonal feature is discussed for Sal Island where measurements suggest that low-level dust transport in winter is replaced by a pronounced high-level Saharan dust layer in summer. The model reproduces this pattern except that there is also significant low level transport in summer, associated mainly with peculiar simulated dust transport events from the western Sahara. On a synoptic scale the frequency of dust outbreaks over the North Atlantic and of major dust deposition events in Spain and a dust vertical profile measured by a lidar over the Azores region are reproduced by the model. Long-term daily monitoring of Saharan dust load over marine areas using Meteosat ISCCP-B2 data, 1, Methodology and preliminary results for 1983-1994 in the western Mediterranean, J. Geophys. Res., 102, 16,947-16,958, 1997a. Moulin, C., F. Dulac, C. E. Lambert, P. Chazette, I. Jankowiak, B. Chatenet, and F. Lavenu, Long-term daily monitoring of Saharan dust load over marine areas using Meteosat ISCCP-B2 data, 2, Accuracy of the method and validation using Sun photometer measurements, J. Geophys. Res., 102, 16,959-16,969, 1997b.
Simulations of Mineral Dust Content With CHIMERE-Dust Model
ABSTRACT
Geometric and aerodynamic surface roughness in the southern Tunisia and their relation with radar backscatter coefficient
... Béatrice Marticorena 1 , Mouldi Kardous 2 , Gilles Bergametti 1 , Yann Callot, Patrick Chazet... more ... Béatrice Marticorena 1 , Mouldi Kardous 2 , Gilles Bergametti 1 , Yann Callot, Patrick Chazette 3, 4 , Houcine Khatteli 2 , Sylvie Le Hégarat-Mascle 5 , Michel Maille 1 , Jean-Louis Rajot 1 , Daniel Vidal-Madjar 5 , Mehrez Zribi 5. (2006). ...
Atmospheric Environment. Part A. General Topics, 1990
It is well recognized that vertical motions play an important role in long range transport (LRT).... more It is well recognized that vertical motions play an important role in long range transport (LRT). The representation of the vertical movements can be obtained by the calculation of isentropic trajectories or by the use of the synoptic vertical wind component {V) to compute three-dimensional (3-D) trajectories. Furthermore, it is easier to compute air mass trajectories using the latter parameter than to compute isentropic ones. This last technique is a very time consuming computer one. On the other hand, the meaning of V, could be questionable by the meteorologist because of its rather poor time and spatial resolutions. The present paper will discuss and validate the use of V: in trajectory models. This validation needs identified meteorological situations leading to characterized vertical motions. We choose the Saharan dust transport from Africa to the Mediterranean region because this situation may well be defined both by the geochemical tracers of dust (AI, Si) and by satellite imagery. Such an experiment has been performed during the period April 1985-April 1986 on Corsica allowing the study of 17 events of dust transport. At first, we show with a meteorological analysis that all these transports are associated to frontal situations. Secondly, we validate the three dimensional trajectory model with horizontal and vertical transport considerations. Horizontal transport and source locations derived from the three-dimensional trajectory model are in very good agreement with lhe satellite observations. The vertical transport, referred to as frontal transport, is determined by comparing the different vertical motions for different final barometric levels. We conclude that, although the isentropic trajectories represent more realistic vertical motions, our model seems to be well adapted to intensive applications in pollution studies.
Modelling the aeolian erosion thresholds on Mars
ABSTRACT
Journal of Geophysical Research, 1991
Beginning in 1985, daily 24-hour aerosol samples were collected on 0.4-pm pore size filters at a ... more Beginning in 1985, daily 24-hour aerosol samples were collected on 0.4-pm pore size filters at a coastal location in northwestern Corsica. Total atmospheric deposition (wet + dry) were sampled between February 1985 and October 1987 with a collection period of about 15 days. As indicated by three-dimentional air mass trajectories, lead aerosol particles collected at this site are primarily derived from European continental source regions. The variability of lead aerosol concentrations on both daily and seasonal time scales is primarily due to the scavenging of lead aerosol particles by rain rather than to changes in source regions. Our results suggest that the ratio between the total atmospheric deposition of Pb and the corresponding mean daily precipitation (mdp) rate is not constant. This ratio reaches a maximum during the Mediterranean summer. We attribute this difference to wet scavenging processes which wash a more loaded atmosphere during the dry season than during the wet season. The precipitation frequency (Fp) is a major factor influencing seasonal variability of the total atmospheric deposition of lead over the western Mediterranean. An intermediate value of Fp allows sufficient reloading of the atmosphere with long-range transported Pb aerosol particles as well as efficient scavenging by precipitation events. SAMPLING AND ANALYSIS works have suggested that this atmospheric lead is Aerosol Sampling
An optimized particle size bin scheme for modeling mineral dust aerosol
Journal of Geophysical Research, 2006
During transport, atmospheric aerosol particles experience nonlinear size-dependent deposition pr... more During transport, atmospheric aerosol particles experience nonlinear size-dependent deposition processes which affect their size distribution. This implies that the aerosol particle size distribution (PSD) should be well represented in three-dimensional transport models that simulate their transport and their radiative or biogeochemical impacts. In particular, mineral dust aerosols exhibit a broad range of particle sizes but the dust PSD is generally
Journal of Geophysical Research, 2007
1] Evaluating the impacts of atmospheric dust on marine ecosystems and climate requires the use o... more 1] Evaluating the impacts of atmospheric dust on marine ecosystems and climate requires the use of three-dimensional transport models including a size-resolved bins scheme to describe the evolution of the particle size distribution. Recently, Forêt et al. (2006) proposed an alternative size bins scheme to better account for the physical size-dependent processes such as dry deposition. This paper evaluates the benefit of using this new bin scheme in three-dimensional transport models. This is achieved by performing a one-and-a-half month simulation with the CHIMERE-DUST model forced by the Mesoscale Model, Version 5 (MM5)/National Center for Environmental Prediction (NCEP) analysis fields, for an area covering the northern Atlantic Sea and the western Africa. Compared to a reference run performed using a large number of size bins (40), our results show that the size bins scheme proposed by reduces at least by a factor of 2 the numerical errors on the simulated concentrations compared to the classical isolog bins scheme for the same number of size bins. However, with this new bins scheme requiring to define the bins according to a dry deposition velocity corresponding to a given friction velocity, we examine the errors associated to this constraint.
Journal of Geophysical Research, 1995
A soil-derived dust emission scheme has been designed to provide an explicit representation of th... more A soil-derived dust emission scheme has been designed to provide an explicit representation of the desert dust sources for the atmospheric transport models dealing with the simulation of the desert dust cycle. Two major factors characterizing the erodible surface are considered: (1) the size distribution of the erodible loose particles of the soil which controls the erosion threshold and the emission strength and (2) the surface roughness which imposes the efficient wind friction velocity acting on the erodible surface. These two parameters are included in a formulation of the threshold wind friction velocity by adapting a size-dependent parameterization proposed by Iversen and White (1982) and by applying to the rough erodible surfaces a drag partition scheme derived from Arya (1975). This White (1979). This allows to attribute a specific production rate to each soil size range for each type of surface. The dust flux F is then considered as a fraction of the total horizontal flux G, the value of the ratio F/G being imposed, at this time, by the soil clay content. In summary, the computed mass fluxes depend on the soil size distribution, the roughness lengths, and the wind friction velocity. The different steps of this scheme have been independently validated by comparison with relevant experimental data. Globally, the agreement is satisfying, so that the dust fluxes could be retrieved with less uncertainties than those observed in previous simulations of the desert dust cycle.
Journal of Geophysical Research, 1997
A physical model was developed to explain threshold friction velocities u., for particles of the ... more A physical model was developed to explain threshold friction velocities u., for particles of the size 60-120 [tm lying on a rough surface in loose soils for semiarid and arid parts of the United States. The model corrected for the effect of momentum absorption by the noncredible roughness. For loose or disturbed soils the most important parameter that controls u., is the aerodynamic roughness height z0. For physical crusts damaged by wind the size of credible crust pieces is important along with the roughness. The presence of cyanobacteriallichen soil crusts roughens the surface, and the biological fibrous growth aggregates soil particles. Only undisturbed sandy soils and disturbed soils of all types would be expected to be credible in normal wind storms. Therefore disturbance of soils by both cattle and humans is very important in predicting wind erosion as continned by our measurements.
Assessing the actual size distribution of atmospheric aerosols collected with a cascade impactor
Journal of Aerosol Science, 1990
ABSTRACT
Comptes Rendus Physique, 2005
This paper presents the Geostationary Fourier Imaging Spectrometer (GeoFIS), a new satellite inst... more This paper presents the Geostationary Fourier Imaging Spectrometer (GeoFIS), a new satellite instrument that has been proposed to monitor tropospheric key pollutants (O 3 , CO) in order to improve the predictive capability of tropospheric chemistry models. The horizontal resolution of GeoFIS is about 15 × 15 km 2 and the temporal resolution is about 60 minutes. It is shown that the current instrument concept (based on available or under development optical, detector and platform technologies) is sufficient to provide tropospheric concentrations of O 3 and CO as well as columns of species like PAN with the required accuracies. To cite this article: J. Orphal et al., C. R. Physique 6 (2005). 2005 Académie des sciences. Published by Elsevier SAS. All rights reserved. Résumé Surveillance de la pollution troposphérique par spectroscopie infrarouge à partir d'une orbite géostationnaire. Dans cet article nous présentons le « Geostationary Fourier Imaging Spectrometer » (GeoFIS), un nouvel instrument satellite qui a été proposé pour surveiller les polluants troposphériques les plus importants (O 3 , CO) afin d'améliorer la précision des prédictions fournies par les modèles de la chimie troposphérique. La résolution horizontale de GeoFIS est de 15 × 15 km 2 environ et la résolution temporelle est de 60 minutes. Nous montrons que le concept actuel de cet instrument (basé sur des technologies optiques, détecteur et plateforme disponibles ou en développement) est bien adapté pour fournir des concentrations troposphériques d'O 3 et de CO, ainsi que des colonnes d'espèces comme le PAN, avec les précisions requises. Pour citer cet article : J. Orphal et al., C. R. Physique 6 (2005).
Assuming an oceanic mixed layer depth of 100 m [Blain et al., 2001] and a few-days residence time... more Assuming an oceanic mixed layer depth of 100 m [Blain et al., 2001] and a few-days residence time of soluble iron in surface waters, atmospheric deposition provides an additional ~10 -5 nmol/L of soluble Fe, whereas the marine concentration is ~1 nmol/L [Blain et al., 2001].
Annales Geophysicae, 1999
Large-scale simulation of the soil-derived dust emission in semi-arid regions needs to account fo... more Large-scale simulation of the soil-derived dust emission in semi-arid regions needs to account for the in¯uence of the soil moisture on the wind erosion threshold. Soil water retention consists of molecular adsorption on the soil grain surface and capillary forces between the grain. Interparticle capillary forces (characterized by the moisture tension) are the main factor responsible for the increase of the wind erosion threshold observed when the soil moisture increases. When the soil moisture content is close to but smaller than the maximum amount of adsorbed water, w¢ (depending on the soil texture), these capillary forces are considered as not strong enough to signi®cantly increase the erosion threshold. An expression of the moisture tension as a function of soil moisture and w¢ is derived from retention curves. From this expression, a parametrization of the ratio of the wet to dry erosion thresholds has been developed as a function of soil moisture and soil texture. The coecients of this parametrization have been determined by using experimental data from the literature. An empirical relationship between w¢ and soil clay content has been established. The erosion threshold ratios simulated for dierent soil textures were found to be in good agreement with the experimental data.
Influence de la teneur en particules de l'atmosphere sur l'efficacite de piegeage des aerosols relation between particulate concentration in the atmosphere and aerosol collection efficiency
Environmental Technology Letters, 1982
ABSTRACT
Inversion of surface NO x anthropogenic emission fluxes in the Paris area during the ESQUIF campaign
Z. Marine Geology 159 1999 241--252
ABSTRACT
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Papers by Bergametti Gilles