J. Pelon

LATMOS, Guyancourt, Île-de-France, France

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Publications (168)264.21 Total impact

  • 01/2015; 8(2):2143-2189. DOI:10.5194/amtd-8-2143-2015
  • Atmospheric Chemistry and Physics 01/2015; 15(6):3497-3516. DOI:10.5194/acp-15-3497-2015 · 5.51 Impact Factor
  • EGU, Vienna, Austria; 04/2014
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    ABSTRACT: A daytime underflight of CALIPSO with the Facility for Airborne Atmospheric Measurements has been performed on 20 September 2012 in the Amazon region, during the biomass burning season. The scene is dominated by a thin elevated layer (aerosol optical depth 0.03 at 532 nm) and a moderately turbid boundary layer (aerosol extinction coefficient ∼110 Mm-1). The boundary layer is topped with small broken stratocumulus clouds. In this complex scene, a comparison of observations from the airborne and spaceborne lidars reveals a few discrepancies. The CALIPSO detection scheme tends to miss the elevated thin layer, and also shows several gaps (∼30%) in the boundary layer. The small clouds are not correctly detected in the atmospheric volume description flags, and are therefore not removed from the signals; this causes the CALIPSO aerosol subtype to oscillate between smoke and polluted dust and may introduce distorsion in the aerosol retrieval scheme. The magnitude of the average extinction coefficient estimated from CALIPSO level 2 data in the boundary layer is as expected, when compared to the aircraft lidar and accounting for wavelength scaling. However, when the gaps in aerosol detection mentioned above are accounted for, we are left with an overall estimate of aerosol extinction for this particular scene that is of the order of two thirds of that determined with the airborne lidar.
    Atmospheric Chemistry and Physics 03/2014; 14(7). DOI:10.5194/acpd-14-9203-2014 · 5.51 Impact Factor
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    ABSTRACT: Lidar and in situ observations performed during POLARCAT campaign are reported here in terms of statistics to characterize aerosol properties over northern Europe using daily airborne measurements conducted between Svalbard Island and Scandinavia from 30 March to 11 April 2008. It is shown that during this period, a rather large number of aerosol layers was observed in the troposphere, with a backscatter ratio at 532 nm of 1.2 (1.5 below 2 km, 1.2 between 5 and 7 km and a minimum in-between). Their sources were identified using multispectral backscatter and depolarization airborne lidar measurements after careful calibration analysis. Transport analysis and comparisons between in situ and airborne lidar observations are also provided to assess the quality of this identification. Comparison with level 1 backscatter observations of the spaceborne CALIOP lidar were done to adjust CALIOP multispectral observations to airborne observations on a statistical basis. Re-calibration for CALIOP daytime 1064 nm signals led to an increase of their values by about 30% in agreement with previous analyses. No re-calibration is made at 532 nm, but scattering ratios appear to be biased low. Regional analyses in the European Arctic then performed as a test, emphasize the potential of the CALIOP spaceborne lidar to further monitor more in depth properties of the aerosol layers over Arctic using infrared and depolarization observations. The CALIOP April 2008 global distribution of the aerosol backscatter reveal two regions with large backscatter below 2 km: the Northern Atlantic between Greenland and Norway, and Northern Siberia. The aerosol color ratio increase between the sources regions and the observations at latitudes above 70° N is consistent with a growth of the aerosol size once transported to the Arctic. The distribution of the aerosol optical properties in the mid troposphere supports the known main transport pathways between mid-latitudes and the Arctic.
    Atmospheric Chemistry and Physics 02/2014; 14(5). DOI:10.5194/acpd-14-5721-2014 · 5.51 Impact Factor
  • 01/2014; 7(8):8777-8816. DOI:10.5194/amtd-7-8777-2014
  • EarthCARE Workshop 2014; 01/2014
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    ABSTRACT: The Saharan Air Layer (SAL) influences large-scale environment from western Africa to eastern tropical Americas, by carrying large amounts of dust aerosols. However, the vertical distribution of the SAL is not well established due to a lack of systematic measurements away from the continents. This can be overcome by using the observations of the spaceborne lidar CALIOP onboard the satellite CALIPSO. By taking advantage of CALIOP's capability to distinguish dust aerosols from other types of aerosols through depolarization, the seasonal vertical distribution of the SAL is analyzed at 1 degrees horizontal resolution over a period of 5 yr (June 2006-May 2011). This study shows that SAL can be identified all year round displaying a clear seasonal cycle. It occurs higher in altitude and more northern in latitude during summer than during winter, but with similar latitudinal extent near Africa for the four seasons. The south border of the SAL is determined by the Intertropical Convergence Zone (ITCZ), which either prohibits dust layers from penetrating it or reduces significantly the number of dust layers seen within or south of it, as over the eastern tropical Atlantic. Spatially, near Africa, it is found between 5 degrees S and 15 degrees N in winter and 5-30 degrees N in summer. Towards the Americas (50 degrees W), SAL is observed between 5 degrees S and 10 degrees N in winter and 10-25 degrees N in summer. During spring and fall, SAL is found between the position of winter and summer not only spatially but also vertically. In winter, SAL occurs in the altitude range 0-3 km off western Africa, decreasing to 0-2 km close to South America. During summer, SAL is found to be thicker and higher near Africa at 1-5 km, reducing to 0-2 km in the Gulf of Mexico, farther west than during the other seasons. SAL is confined to one layer, of which the mean alti-tude decreases with westward transport by 13 mdeg(-1) during winter and 28mdeg(-1), after 30 degrees W, during summer. Its mean geometrical thickness decreases by 25mdeg(-1) in winter and 9mdeg(-1) in summer. Spring and fall present similar characteristics for both mean altitude and geometrical thickness. Wind plays a major role not only for the transport of dust within the SAL but also by sculpting it. During winter, the trade winds transport SAL towards South America, while in spring and summer they bring dust-free maritime air masses mainly from the North Atlantic up to about 50 degrees W below the SAL. The North Atlantic westerlies, with their southern border occurring between 15 and 30 ffi N (depending on the season, the longitude and the altitude), prevent the SAL from developing further northward. In addition, their southward shift with altitude gives SAL its characteristic oval shape in the northern part. The effective dry deposition velocity of dust particles is estimated to be 0.07 cms(-1) in winter, 0.14 cms(-1) in spring, 0.2 cms(-1) in summer and 0.11 cms(-1) in fall. Finally, the African Easterly Jet (AEJ) is observed to collocate with the maximum dust load of the SAL, and this might promote the differential advection for SAL parts, especially during summer.
    Atmospheric Chemistry and Physics 11/2013; DOI:10.5194/acp-13-11235-2013 · 4.88 Impact Factor
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    ABSTRACT: [1] This paper presents the implementation of a new version of the DARDAR (radar lidar) classification derived from CloudSat and CALIPSO data. The resulting target classification called DARDAR v2 is compared to the first version called DARDAR v1. Overall DARDAR v1 reports more cloud or rain pixels than DARDAR v2. In the low troposphere this is because v1 detects too many liquid cloud pixels, and in the higher troposphere this is because v2 is more restrictive in lidar detection than v1. Nevertheless, the spatial distribution of different types of hydrometeors show similar patterns in both classifications. The French airborne Radar-Lidar (RALI) platform carries a CloudSat/CALIPSO instrument configuration (lidar at a wavelength of 532nm and a 95GHz cloud radar) as well as an EarthCare instrument configuration (high spectral resolution lidar at 355nm and a 95GHz Doppler cloud radar). It therefore represents an ideal go-between for A-Train and EarthCare. The DARDAR v2 classification algorithm is adapted to RALI data for A-Train overpasses during dedicated airborne field experiments using the lidar at 532nm and the radar Doppler measurements. The results from the RALI classification are compared with the DARDAR v2 classification to identify where the classification should still be interpreted with caution. Finally, the RALI classification algorithm with lidar at 532nm is adapted to RALI with high spectral resolution lidar data at 355nm in preparation for EarthCare.
    07/2013; 118(14). DOI:10.1002/jgrd.50579
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    ABSTRACT: Major disruptions of the aviation system from recent volcanic eruptions have intensified discussions about and increased the international consensus toward improving volcanic ash warnings. Central to making progress is to better discern low volcanic ash loadings and to describe the ash cloud structure more accurately in three-dimensional space and time. Here, dispersed volcanic ash observed by the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) space-based lidar near 20 000-40 000 ft [~(6-13) km] over Australia and New Zealand during June 2011 is studied. This ash event took place 3 weeks after the Puyehue-Cordon Caulle eruption, which disrupted air traffic in much of the Southern Hemisphere. The volcanic ash layers are shown to exhibit color ratios (1064/532 nm) near 0.5, significantly lower than unity, as is observed with ice. Those optical properties are used to develop an ash detection algorithm. A "trajectory mapping" technique is then demonstrated wherein ash cloud observations are ingested into a Lagrangian model and used to construct ash dispersion maps and cross sections. Comparisons of the model results with independent observations suggest that the model successfully reproduces the 3D structure of volcanic ash clouds. This technique has a potential operational application in providing important additional information to worldwide volcanic ash advisory centers.
    Journal of Applied Meteorology and Climatology 07/2013; 52(9). DOI:10.1175/JAMC-D-12-0279.1 · 2.10 Impact Factor
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    ABSTRACT: We analyzed different models to estimate absorption at W-band by gaseous species by taking advantage of the collocated CloudSat-Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) measurements. We used the power backscattered by the surface in the green visible wavelength of the lidar of CALIPSO as a reference to infer CloudSat's 94-GHz ocean surface backscatter in clear air and infer the attenuation introduced by gaseous absorption. Different millimeter-wave propagation models (MPMs) and different sources to determine the profile of atmospheric thermodynamic state are used to estimate CloudSat attenuation. These estimates are compared to the observations to calculate the residual dispersion. We show here that we need to adjust the empirical constants of preexisting water vapor absorption models to minimize the dispersion. Our results indicate an overestimation of absorption by the water vapor continuum at 94 GHz in Liebe-based MPM. We also propose a new empirical model to better represent the absorption of the water vapor continuum near 94 GHz. When this model is used in combination with the Advanced Microwave Scanning Radiometer for the Earth Observing System water vapor path and the Global Modeling and Assimilation Office water vapor vertical profile distribution, it leads to the lowest dispersion of the data on a statistical basis (global data over one month). The improved model is expected to optimize water vapor correction applied to CloudSat data and, potentially, also to improve interpretation of brightness temperature measurements in the W-band (e.g., 85- and 98-GHz radiometric channels).
    IEEE Transactions on Geoscience and Remote Sensing 07/2013; 51(7). DOI:10.1109/TGRS.2012.2228659 · 2.93 Impact Factor
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    ABSTRACT: A statistical linear relationship between NO2 surface concentration and its integrated content in the atmospheric boundary layer (ABL) is established in urban conditions, using ABL depth as an ancillary parameter. This relationship relies on a unique data set including 20 months of observations from a ground-based UV-visible light spectrometer and from an aerosol lidar, both located in Paris inner city center. Measurements show that in all seasons, large vertical gradients of NO2 concentration exist in Paris developed ABL, explaining why the average concentration retrieved is only about 25% of NO2 surface concentration. This result shows that the commonly used hypothesis of constant mixing ratio in the ABL is not valid over urban areas, where large NOx emissions occur. Moreover, the relationship obtained is robust, and the studied area lacks of any particular orographic features, so that our results should be more widely applicable to pollution survey from space-borne observations.
    03/2013; 40(6):n/a-n/a. DOI:10.1002/grl.50242
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    ABSTRACT: Two complementary case studies are conducted to analyse convective system properties in the region where strong cloud-top lidar backscatter anomalies are observed as reported by Platt et al. (2011). These anomalies were reported for the first time using in-situ microphysical measurements in an isolated continental convective cloud over Germany during the CIRCLE2 experiment (Gayet et al., 2012). In this case, quasi collocated in situ observations with CALIPSO, CloudSat and Meteosat-9/SEVIRI observations confirm that regions of backscatter anomalies represent the most active and dense convective cloud parts with likely the strongest core updrafts and unusual high values of the particle concentration, extinction and ice water content (IWC), with the occurrence of small ice crystal sizes. Similar spaceborne observations are then analyzed in a maritime mesoscale cloud system (MCS) on 20 June 2008 located off the Brazil coast between 0° and 3° N latitude. Near cloud-top backscatter anomalies are evidenced in a region which corresponds to the coldest temperatures with maximum cloud top altitudes derived from collocated CALIPSO/IIR and Meteosat-9/SEVIRI infrared brightness temperatures. The interpretation of CALIOP data highlights significant differences of microphysical properties from those observed in the continental isolated convective cloud. Indeed, SEVIRI retrievals in the visible confirm much smaller ice particles near-top of the isolated continental convective cloud, i.e. effective radius (Reff) ~15 μm against 22–27 μm in the whole MCS area. 94 GHz Cloud Profiling Radar observations from CloudSat are then used to describe the properties of the most active cloud regions at and below cloud top. The cloud ice water content and effective radius retrieved with the CloudSat 2B-IWC and DARDAR inversion techniques, show that at usual cruise altitudes of commercial aircraft (FL 350 or ~10 700 m level), high IWC (i.e. up to 2 to 4 g m−3) could be identified according to specific IWC-Z relationships. These values correspond to a maximum reflectivity factor of +18 dBZ (at 94 GHz). Near-top cloud properties also indicate signatures of microphysical characteristics according to the cloud-stage evolution as revealed by SEVIRI images to identify the development of new cells within the MCS cluster. It is argued that the availability of real time information of the km-scale cloud top IR brightness temperature decrease with respect to the cloud environment would help identify MCS cloud areas with potentially high ice water content and small particle sizes against which onboard meteorological radar may not be suitable to provide timely warning.
    Atmospheric Chemistry and Physics 01/2013; 14(2013):22535-22574. DOI:10.5194/acp-14-899-2014 · 4.88 Impact Factor
  • Journal of Atmospheric and Oceanic Technology 07/2012; 29:911-921. DOI:10.1175/JTECH-D-11-00040.1 · 1.82 Impact Factor
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    ABSTRACT: A central question to understanding the climate of North Africa is to better comprehend and explain the existence of the Central Saharan dust loading maxima in summer. This dust 'hotspot' has been apparent in many satellite products. However, The actual physical processes involved are not clear. Indeed, qualitative maps of dust emissions suggest that emission sources are not co-located with the aerosol optical depth maximum. Therefore, it is not known to what extent the hotspot represents local emission and/or transport from remote emission sources. In this work, we aim to address this question by analysis of the long-term six year Level 1 and 2 Caliop data archive. The vertical profiles of aerosol from the caliop lidar potentially enables identification and quantification of active dust emission events. We then classify emission events according to the driving meteorological processes (e.g. harmatan flow, monsoon flow, mixing of low level jets, cold pools, etc.) from coincident analysis/reanalysis fields. This identification from caliop and classification of processes is based on a set of 'rules' informed by analysis of dust events during the Fennec project observational campaign.
  • 04/2012; 8(22):14. DOI:10.4267/2042/47046
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    04/2012; 8(16):11. DOI:10.4267/2042/47000
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    ABSTRACT: Recent studies using satellite observations show that numerous dust sources are located in the foothills of the Saharan mountains. Generally, dust emission is closely related to sediment supply and surface wind. Thus, dust emission can be inhibited by either lack of high wind speeds or by unsuitable surface characteristics. Significant rainfall and flash flood events have been proposed to lead to changes in pluvial sediment supplies in mountain drainage systems. These sediments are suitable for dust uplift and assumed to have a main contribution to the dust emission fluxes over these areas. This mechanism could help to explain the observed marked interannual variability of some dust sources, which is currently not well understood. This study uses a novel combination of airborne and space-borne measurements to explore dust sources within complex terrain. It consists of two main parts: First, dust emission forced by the break-down of nocturnal low-level jets is investigated by analysing data from the RAIN4DUST/FENNEC-France aircraft campaign in June 2011 based at Fuerteventura, Spain. Local dust emission over North Mauritania is observed using a combination of different measurement systems flying aboard the French Falcon FA20, such as high resolution aerial ground camera, high-resolution lidar instrument and drop-sondes. The orientation of the flight legs allows for the characterisation of the evolution of a developing dust plume in time and space combining information on ground surface structure and vertical dust distribution. Supplementary analysis of model simulations and satellite remote sensing products provide additional information on the location of dust sources and dust transport paths. Second, the role of pluvial sediment supply for dust emission in desert valleys is investigated. For a selected area over West Africa ENVISAT SAR (synthetic aperture radar) measurements from 2003-2010 are analysed to identify changes in surface sediments through loss of coherence between two consecutive images. Results from this study highlight the contribution of flash floods for dust sources located within complex terrain. Together the two approaches provide a detailed picture of dust emission from sources within complex terrain revealing controls on dust emission from both atmospheric factors and sediment supply.
    EGU 2012; 04/2012
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    ABSTRACT: Water vapor measurements from a Raman lidar developed conjointly by the IGN and the LATMOS/CNRS are used for documenting the water vapor heterogeneities and correcting GPS signal propagation delays in clear sky conditions. We use data from four 6 h-observing sessions during the VAPIC experiment (15 May–15 June 2004). The retrieval of zenith wet delays (ZWDs) from our Raman lidar is shown to agree well with radiosonde (0.6 ± 2.5 mm) and microwave radiometers (−6.6 ± 1.2 and 6.0 ± 3.8 mm) retrievals. ZWDs estimated from GPS data present a good consistency too (−2.0 ± 2.7 mm) but they are still shown to not represent properly the fast evolutions with high frequency variations correlation about 0.12. Part of the errors is also due to multipath and antenna phase center variations. Within this framework, methodologies for integrating of zenith lidar observations into the GPS processing are described. They include also a correction for multipath and antenna phase center variation. The best results are obtained when the lidar ZWDs are used for a priori correcting the GPS phase observations: discrepancies between lidar and GPS estimates are then reduced to −1.1 ± 1.4 mm. It is shown also that mapping function derived from the lidar vertical profiles performs nearly as well as the VMF1 mapping function.
    01/2012: pages 795-800;
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    ABSTRACT: This study reports on the optical and microphysical characterization of particles contained in volcanic ash clouds using thermal infrared radiometry. Several works have shown the potential of the split window technique for estimating the effective particle size and optical thickness of semi-transparent clouds from two channels in the infrared atmospheric window (8 - 12 μm). In the present study, this approach is applied to the characterization of volcanic particles. The inversion algorithm is based on LUTs built with an accurate radiative transfer code, including gaseous absorption as well as multiple scattering and absorption by particles. Realistic spectral variations for optical properties of several types of volcanic particle (Ash, H2SO4 ...) and water or ice clouds have been calculated from refractive indices and Mie theory. In addition, this inversion procedure needs to define the altitude, temperature and thickness of the ash cloud. Consequently, meteorological data relative to the atmosphere and the state of ash cloud have been calculated using the Regional Atmospheric Modeling System (RAMS). This model allows giving a 3D dynamical transport of the ash plume and its vertical distribution. Ash sources and scenes area have been studied in detail with higher resolution using nested grid system of the model. In a first step, a sensitivity study based on radiative transfer calculations is presented in order to illustrate the potential of this approach. This technique is then applied to volcanic plumes in April-May 2010. Brightness temperatures from the MODIS spectroradiometer, the Infrared Imaging Radiometer (IIR) and the SEVIRI radiometer are used for some scenes acquired simultaneously over North / West of Europe with similar spectral or spatial resolutions. Spatial distribution of the retrieved optical thickness and effective size of particles are presented and analyzed. Comparisons between retrievals from IIR, MODIS and SEVIRI are presented. Contributions of the spectral channels to retrievals, as well as the influence of the particle type are also discussed.

Publication Stats

2k Citations
264.21 Total Impact Points

Institutions

  • 2014
    • LATMOS
      Guyancourt, Île-de-France, France
  • 2009–2014
    • Université de Versailles Saint-Quentin
      Versailles, Île-de-France, France
  • 1989–2013
    • Pierre and Marie Curie University - Paris 6
      Lutetia Parisorum, Île-de-France, France
  • 1980–2010
    • French National Centre for Scientific Research
      • • Laboratoire d'aérologie (LA)
      • • Laboratoire de météorologie dynamique (LMD)
      Lutetia Parisorum, Île-de-France, France
  • 1995–2008
    • Institut Pierre Simon Laplace
      Lutetia Parisorum, Île-de-France, France
  • 2003
    • Hampton VA Medical Center
      Hampton, Virginia, United States
    • Université du Littoral Côte d'Opale (ULCO)
      Dunkirk, Nord-Pas-de-Calais, France
  • 2002
    • Polytech Paris-UPMC
      Lutetia Parisorum, Île-de-France, France
  • 1999
    • NASA
      Вашингтон, West Virginia, United States