Published under the terms of the Creative Commons Attribution-Noncommercial 3.0 Unported LicenseVertical profiles of the linear particle depolarization ratio of pure dust clouds were measured during the Saharan Mineral Dust Experiment (SAMUM) at Ouarzazate, Morocco (30.9 degrees N, -6.9 degrees E), close to source regions in May-June 2006, with four lidar systems at four wavelengths (355, 532, 710 and 1064 nm). The intercomparison of the lidar systems is accompanied by a discussion of the different calibration methods, including a new, advanced method, and a detailed error analysis. Over the whole SAMUM periode pure dust layers show a mean linear particle depolarization ratio at 532 nm of 0.31, in the range between 0.27 and 0.35, with a mean angstrom ngstrom exponent (AE, 440-870 nm) of 0.18 (range 0.04-0.34) and still high mean linear particle depolarization ratio between 0.21 and 0.25 during periods with aerosol optical thickness less than 0.1, with a mean AE of 0.76 (range 0.65-1.00), which represents a negative correlation of the linear particle depolarization ratio with the AE. A slight decrease of the linear particle depolarization ratio with wavelength was found between 532 and 1064 nm from 0.31 +/- 0.03 to 0.27 +/- 0.04

North Africa is the world’s largest source of dust, a large part of which is transported across the Atlantic to the Caribbean and beyond where it can impact radiation and clouds. Many aspects of this transport and its climate effects remain speculative. The Saharan Aerosol Long-Range Transport and Aerosol–Cloud-Interaction Experiment (SALTRACE; www.pa.op.dlr.de/saltrace) linked ground-based and airborne measurements with remote sensing and modeling techniques to address these issues in a program that took place in 2013/14. Specific objectives were to 1) characterize the chemical, microphysical, and optical properties of dust in the Caribbean, 2) quantify the impact of physical and chemical changes (“aging”) on the radiation budget and cloud microphysical processes, 3) investigate the meteorological context of transatlantic dust transport, and 4) assess the roles of removal processes during transport. SALTRACE was a German-led initiative involving scientists from Europe, Cabo Verde, the Caribbean, and the United States. The Falcon research aircraft of the Deutsches Zentrum für Luft- und Raumfahrt (DLR), equipped with a comprehensive aerosol and wind lidar payload, played a central role. Several major dust outbreaks were studied with 86 h of flight time under different conditions, making it by far the most extensive investigation on long-range transported dust ever made. This article presents an overview of SALTRACE and highlights selected results including data from transatlantic flights in coherent air masses separated by more than 4,000-km distance that enabled measurements of transport effects on dust properties. SALTRACE will improve our knowledge on the role of mineral dust in the climate system and provide data for studies on dust interactions with clouds, radiation, and health.

Routine aerosol measurements have been carried out at INTA-El Arenosillo (Huelva, Spain) since February 2000 with a Cimel sun photometer integrated in the global aerosol monitoring network AERONET. A 5-year aerosol database allows characterization and classification of aerosol properties, which define the local aerosol climatology. In this work two basic parameters for aerosol characterization, aerosol optical depth (AOD) andÅngström exponent, α, are used for aerosol analysis. The mean AOD is 0.18 (±0.14) and the mean α is 1.05 (±0.43). The AOD presents two peaks during the year, at the end of the winter and during the summer, which are related to the seasonal patterns of the desert dust aerosols which arrive at the south-western Iberian Peninsula from North Africa. TheÅngström exponent presents two frequency modes, related to the two main aerosol types present at El Arenosillo: coastal marine aerosols and desert dust. A main aerosol scenario (66% of data) is defined as coastal marine aerosols, with the influence of local sources of continental and polluted aerosols. Continental aerosols are present in 11% of cases, while the desert dust has a very relevant occurrence in around 20% of the data.

T E L L U SCharacterization of Saharan dust, marine aerosols and mixtures of biomass-burning aerosols and dust by means of multi-wavelength depolarization and Raman lidar measurements during SAMUM 2 A B S T R A C T The particle linear depolarization ratio δ p of Saharan dust, marine aerosols and mixtures of biomass-burning aerosols from southern West Africa and Saharan dust was determined at three wavelengths with three lidar systems during the SAharan Mineral dUst experiMent 2 at the airport of Praia, Cape Verde, between 22 January and 9 February 2008. The lidar ratio S p of these major types of tropospheric aerosols was analysed at two wavelengths. For Saharan dust, we find wavelength dependent mean particle linear depolarization ratios δ p of 0.24-0.27 at 355 nm, 0.29-0.31 at 532 nm and 0.36-0.40 at 710 nm, and wavelength independent mean lidar ratios S p of 48-70 sr. Mixtures of biomass-burning aerosols and dust show wavelength independent values of δ p and S p between 0.12-0.23 and 57-98 sr, respectively. The mean values of marine aerosols range independent of wavelength for δ p from 0.01 to 0.03 and for S p from 14 to 24 sr.

Abstract. Dual-wavelength Raman and depolarization lidar observations were performed during the Saharan Aerosol Long-range Transport and Aerosol-Cloud interaction Experiment in Barbados in June and July 2013 to characterize the optical properties and vertical distribution of long-range transported Saharan dust after transport across the Atlantic Ocean. Four major dust events were studied during the measurements from 15 June to 13 July 2013 with aerosol optical depths at 532 nm of up to 0.6. The vertical aerosol distribution was characterized by a three-layer structure consisting of the boundary layer, the entrainment or mixing layer and the pure Saharan dust layer. The upper boundary of the pure dust layer reached up to 4.5 km in height. The contribution of the pure dust layer was about half of the total aerosol optical depth at 532 nm. The total dust contribution was about 50-70 % of the total aerosol optical depth at 532 nm. The lidar ratio within the pure dust layer was found to be wavelength independent with mean values of 53 ± 5 sr at 355 nm and 56 ± 7 sr at 532 nm. For the particle linear depolarization ratio, wavelength-independent mean values of 0.26 ± 0.03 at 355 nm and 0.27 ± 0.01 at 532 nm have been found.