Long‐range transport of Saharan dust to northern Europe: The 11–16 October 2001 outbreak observed with EARLINET

Abstract. We use CALIOP nighttime measurements of lidar backscatter, color and depolarization ratios, as well as particulate retrievals during the summer of 2007 to study transatlantic dust properties downwind of Saharan sources, and to examine the influence of nearby clouds on dust. Our analysis suggests that (1) under clear skies, while lidar backscatter and color ratio do not change much with altitude and longitude in the Saharan Air Layer (SAL), depolarization ratio increases with altitude and decreases westward in the SAL; (2) the vertical lapse rate of dust depolarization ratio, introduced here, increases within SAL as plumes move westward; (3) nearby clouds barely affect the backscatter and color ratio of dust volumes within SAL but not so below SAL. Moreover, the presence of nearby clouds tends to decrease the depolarization of dust volumes within SAL. Finally, (4) the odds of CALIOP finding dust below SAL next to clouds are about 2/3 of those far away from clouds. This feature, together with an apparent increase in depolarization ratio near clouds, indicates that particles in some dust volumes loose asphericity in the humid air near clouds, and cannot be identified by CALIPSO as dust.

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“…In addition, we note that the depolarization ratio is predominantly influenced by asphericity of the dust particles (e.g. Ansmann et al, 2003).…”

Section: Relationship Of Depolarization Ratio With Color Ratiomentioning

confidence: 99%

CALIPSO observations of transatlantic dust: vertical stratification and effect of clouds

et al. 2012

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“…Shin et al, 2013;Ansmann et al, 2003;Freudenthaler et al, 2009;Sassen et al, 2007) presented results related to a single-type of aerosol, i.e. mineral dust.…”

Section: A Nemuc Et Al: Assessment Of Aerosol's Mass Concentrationsmentioning

confidence: 99%

Assessment of aerosol's mass concentrations from measured linear particle depolarization ratio (vertically resolved) and simulations

et al. 2013

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Abstract. Multi-wavelength depolarization Raman lidar measurements from Magurele, Romania are used in this study along with simulated mass-extinction efficiencies to calculate the mass concentration profiles of different atmospheric components, due to their different depolarization contribution to the 532 nm backscatter coefficient. Linear particle depolarization ratio (δ part ) was computed using the relative amplification factor and the system-dependent molecular depolarization. The low depolarizing component was considered as urban/smoke, with a mean δ part of 3 %, while for the high depolarizing component (mineral dust) a mean δ part of 35 % was assumed.For this study 11 months of lidar measurements were analysed. Two study cases are presented in details: one for a typical Saharan dust aerosol intrusion, 10 June 2012 and one for 12 July 2012 when a lofted layer consisting of biomass burning smoke extended from 3 to 4.5 km height.Optical Properties of Aerosols and Clouds software package (OPAC) classification and conversion factors were used to calculate mass concentrations. We found that calibrated depolarization measurements are critical in distinguishing between smoke-reach aerosol during the winter and dustreach aerosol during the summer, as well as between elevated aerosol layers having different origins. Good agreement was found between lidar retrievals and DREAM-Dust REgional Atmospheric Model forecasts in cases of Saharan dust. Our method was also compared against LIRIC (The Lidar/Radiometer Inversion Code) and very small differences were observed.

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“…In Europe, systematic Saharan dust studies with polarization lidars began in the 1990s (Gobbi, 1998;Gobbi et al, 2000;di Sarra et al, 2001). Dust was investigated later on by means of polarization lidar in the framework of the European Aerosol Research Lidar Network (e.g., Ansmann et al, 2003). All of the ground-based observations, conducted before SALTRACE, were based on single-wavelength lidar observations, although several single-wavelength-lidar systems were combined during dedicated field campaigns such as SAMUM-1 and 2 Groß et al, 2011b;Tesche et al, 2011a).…”

Section: Triple-wavelength Polarization Lidar Berthamentioning

confidence: 99%

Triple-wavelength depolarization-ratio profiling of Saharan dust over Barbados during SALTRACE in 2013 and 2014

et al. 2017

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Abstract. Triple-wavelength polarization lidar measurements in Saharan dust layers were performed at Barbados (13.1 • N, 59.6 • W), 5000-8000 km west of the Saharan dust sources, in the framework of the Saharan Aerosol Longrange Transport and Aerosol-Cloud-Interaction Experiment (SALTRACE-1, June-July 2013, SALTRACE-3, June-July 2014). Three case studies are discussed. High quality was achieved by comparing the dust linear depolarization ratio profiles measured at 355, 532, and 1064 nm with respective dual-wavelength (355, 532 nm) depolarization ratio profiles measured with a reference lidar. A unique case of long-range transported dust over more than 12 000 km is presented. Saharan dust plumes crossing Barbados were measured with an airborne triple-wavelength polarization lidar over Missouri in the midwestern United States 7 days later. Similar dust optical properties and depolarization features were observed over both sites indicating almost unchanged dust properties within this 1 week of travel from the Caribbean to the United States. The main results of the triple-wavelength polarization lidar observations in the Caribbean in the summer seasons of 2013 and 2014 are summarized. On average, the particle linear depolarization ratios for aged Saharan dust were found to be 0.252 ± 0.030 at 355 nm, 0.280 ± 0.020 at 532 nm, and 0.225 ± 0.022 at 1064 nm after approximately 1 week of transport over the tropical Atlantic. Based on published simulation studies we present an attempt to explain the spectral features of the depolarization ratio of irregularly shaped mineral dust particles, and conclude that most of the irregularly shaped coarse-mode dust particles (particles with diameters > 1 µm) have sizes around 1.5-2 µm. The SALTRACE results are also set into the context of the SAMUM-1 (Morocco, 2006) and SAMUM-2 (Cabo Verde, 2008) depolarization ratio studies. Again, only minor changes in the dust depolarization characteristics were observed on the way from the Saharan dust sources towards the Caribbean.

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Long‐range transport of Saharan dust to northern Europe: The 11–16 October 2001 outbreak observed with EARLINET

Cited by 287 publications

References 37 publications

CALIPSO observations of transatlantic dust: vertical stratification and effect of clouds

CALIPSO observations of transatlantic dust: vertical stratification and effect of clouds

Assessment of aerosol's mass concentrations from measured linear particle depolarization ratio (vertically resolved) and simulations

Triple-wavelength depolarization-ratio profiling of Saharan dust over Barbados during SALTRACE in 2013 and 2014

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