J. Pelon

UPMC, Pittsburgh, Pennsylvania, United States

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Publications (179)303.91 Total impact

  • 01/2015; 8(2):2143-2189. DOI:10.5194/amtd-8-2143-2015
  • Atmospheric Chemistry and Physics 01/2015; 15(7):3831-3850. DOI:10.5194/acp-15-3831-2015 · 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
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    ABSTRACT: Recently, two Types of Ice Clouds (TICs) properties have been characterized using ISDAC airborne measurements (Alaska, April 2008). TIC-2B were characterized by fewer (<10 L-1) and larger (>110 μm) ice crystals, a larger ice supersaturation (>15%) and a fewer ice nuclei (IN) concentration (<2 order of magnitude) when compared to TIC-1/2A. It has been hypothesized that emissions of SO2 may reduce the ice nucleating properties of IN through acidification, resulting to a smaller concentration of larger ice crystals and leading to precipitation (e.g. cloud regime TIC-2B) because of the reduced competition for the same available moisture. Here, the origin of air masses forming the ISDAC TIC-1/2A (1 April 2008) and TIC-2B (15 April 2008) is investigated using trajectory tools and satellite data. Results show that the synoptic conditions favor air masses transport from the three potentials SO2 emission areas to Alaska: eastern China and Siberia where anthropogenic and biomass burning emission respectively are produced and the volcanic region from the Kamchatka/Aleutians. Weather conditions allow the accumulation of pollutants from eastern China/Siberia over Alaska, most probably with the contribution of acid volcanic aerosol during the TIC-2B period. OMI observations reveal that SO2 concentrations in air masses forming the TIC-2B were larger than in air masses forming the TIC-1/2A. Airborne measurements show high acidity near the TIC-2B flight where humidity was low. These results strongly support the hypothesis that acidic coating on IN are at the origin of the formation of TIC-2B.
    Atmospheric Chemistry and Physics 01/2014; 14(3). DOI:10.5194/acpd-13-4331-2013 · 5.51 Impact Factor
  • EarthCARE Workshop 2014; 01/2014
  • 01/2014; 7(8):8777-8816. DOI:10.5194/amtd-7-8777-2014
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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: The Eyjafjallajökull eruption during May 2010 is used as a case study to evaluate the consistency of retrievals from different thermal infrared instruments for the detection and characterization of volcanic ash plumes. In this study, the split window technique is used to estimate the optical thickness, the effective particle size and the mass concentration of volcanic particles from brightness temperatures measured in the infrared atmospheric window (8-12 μm). Retrievals are obtained for several mineral compositions whose optical properties are computed using Mie theory accounting for spectral variations of the refractive index. The method is applied similarly to data from MODIS, SEVIRI and IASI space-borne instruments, using two channels at 11 μm and 12 μm. Despite different instrumental characteristics, the results are in good agreement, which denotes the robustness of the retrieval method and the consistency of the observations. Nevertheless, the refractive index data and altitude used for the plume in the inversion may lead to large uncertainties in retrieved effective size and mass concentration in dense plumes and makes it difficult to estimate its composition. While it brings additional constrains, the use of a third channel (8.7 μm) does not allow determining the nature of the particles. As confirmed with high spectral resolution radiative transfer simulations, hyperspectral sensors, such as IASI, are well-suited to study the particle composition of volcanic plumes.
    Atmospheric Measurement Techniques 03/2013; 6(2):2793-2828. DOI:10.5194/amtd-6-2793-2013 · 3.21 Impact Factor
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    ABSTRACT: The Development of Methodologies for Water Vapour Measurement (DEMEVAP) project aims at assessing and improving humidity sounding techniques and establishing a reference system based on the combination of Raman lidars, ground-based sensors and GPS. Such a system may be used for climate monitoring, radiosonde bias detection and correction, satellite measurement calibration/validation, and mm-level geodetic positioning with Global Navigation Satellite Systems. A field experiment was conducted in September-October 2011 at Observatoire de Haute Provence. Two Raman lidars, a stellar spectrometer (SOPHIE), a differential absorption spectrometer (SAOZ), a sun photometer (AERONET), 5 GPS receivers and 4 types of radiosondes (Vaisala RS92, MODEM M2K2-DC and M10, and Meteolabor Snow-White) participated in the campaign. A total of 26 balloons with multiple radiosondes were flown during 16 clear nights. This paper presents preliminary findings from the analysis of all these datasets. Several classical Raman lidar calibration methods are evaluated which use either Vaisala RS92 measurements, point capacitive humidity measurements, or GPS integrated water vapour (IWV) measurements. A novel method proposed by Bosser et al. (2010) is also tested. It consists in calibrating the lidar measurements during the GPS data processing. The methods achieve a repeatability of 4-5%. A drift in the IGN-LATMOS Raman lidar calibration of 15% over the 45 days of the experiment is evidenced but not yet explained. When this drift is removed, the precision of the calibration factors improves to 2-3%. However, the variations in the absolute calibration factor between methods and types of reference data remain at the level of 7%. The intercomparison of radiosonde measurements shows good agreement between RS92 and Snow-White measurements up to 12 km. An overall dry bias is found in the measurements from both MODEM radiosondes. Investigation of situations with low RH values (<10%) in the lower and middle troposphere reveals, on occasion, a lower RH detection limit in the Snow-White measurements compared to RS92 due to a saturation of the Peltier device. However, on other occasions, a dry bias is found in RS92, instead. Raman lidar water vapour measurements were useful to distinguish between which of the radiosondes was biased. On average, both RS92 and Snow-White measurements show a slight moist bias at night-time compared to GPS IWV, while the MODEM measurements show a large dry bias. The spectrometer IWV measurements contained a large bias that is currently under investigation. The sun photometer (daytime) and calibrated Raman lidar (night-time) IWV measurements showed excellent agreement with the GPS IWV measurements.
    Atmospheric Measurement Techniques 01/2013; 6(2-2):3439-3509. DOI:10.5194/amtd-6-3439-2013 · 3.21 Impact Factor
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    ABSTRACT: Cirrus are cloud types that are recognized to have a strong impact on the Earth-atmosphere radiation balance. This impact is however still poorly understood, due to the difficulties in describing the large variability of their properties in global climate models. Consequently, numerous airborne and space-borne missions have been dedicated to their study in the last decades. The satellite constellation A-Train has for instance proven to be particularly helpful for the study of cirrus. More particularly, the Infrared Imaging Radiometer (IIR) carried onboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite shows a great sensitivity to the radiative and microphysical properties of these clouds. Our study presents a novel methodology that uses the thermal infrared measurements of IIR to retrieve the ice crystal effective size and optical thickness of cirrus. This methodology is based on an optimal estimation scheme, which possesses the advantage of attributing precise uncertainties to the retrieved parameters. Two IIR airborne validation campaigns have been chosen as case studies for illustrating the results of our retrieval method. It is observed that optical thicknesses could be accurately retrieved but that large uncertainties may occur on the effective diameters. Strong agreements have also been found between the products of our method when separately applied to the measurements of IIR and of the airborne radiometer CLIMAT-AV, which consolidates the results of previous validation studies of IIR level-1 measurements. Comparisons with in situ observations and with operational products of IIR are also discussed and appear to be coherent with our results. However, we have found that the quality of our retrievals can be strongly impacted by uncertainties related to the choice of a pristine crystal model and by poor constraints on the properties of possible liquid cloud layers underneath cirrus. Simultaneous retrievals of liquid clouds radiative and microphysical properties and/or the use of different ice crystal models should therefore be considered in order to improve the quality of the results.
    Atmospheric Chemistry and Physics 01/2013; 13(16-2):5553-5599. DOI:10.5194/acpd-13-5553-2013 · 4.88 Impact Factor
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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

Publication Stats

2k Citations
303.91 Total Impact Points


  • 2014
    • UPMC
      Pittsburgh, Pennsylvania, United States
  • 2013–2014
    • 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
    • Université du Littoral Côte d'Opale (ULCO)
      Dunkirk, Nord-Pas-de-Calais, France
    • Hampton VA Medical Center
      Hampton, Virginia, United States
  • 2002
    • Polytech Paris-UPMC
      Lutetia Parisorum, Île-de-France, France
  • 1999
    • NASA
      Вашингтон, West Virginia, United States