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- ItemCharacterization 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(Milton Park : Taylor & Francis, 2017) Groß, Silke; Tesche, Matthias; Freudenthaler, Volker; Toledano, Carlos; Wiegner, Matthias; Ansmann, Albert; Althausen, Dietrich; Seefeldner, MeinhardThe particle linear depolarization ratio δp 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 Sp of these major types of tropospheric aerosols was analysed at two wavelengths. For Saharan dust, we find wavelength dependent mean particle linear depolarization ratios δp 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 Sp of 48–70 sr. Mixtures of biomass-burning aerosols and dust show wavelength independent values of δp and Sp between 0.12–0.23 and 57–98 sr, respectively. The mean values of marine aerosols range independent of wavelength for δp from 0.01 to 0.03 and for Sp from 14 to 24 sr.
- ItemVertical profiling of Saharan dust with Raman lidars and airborne HSRL in southern Morocco during SAMUM(Milton Park : Taylor & Francis, 2017) Tesche, Matthias; Ansmann, Albert; MüLLER, Detlef; Althausen, Dietrich; Mattis, Ina; Heese, Birgit; Freudenthaler, Volker; Wiegner, Matthias; Esselborn, Michael; Pisani, Gianluca; Knippertz, PeterThree ground-based Raman lidars and an airborne high-spectral-resolution lidar (HSRL) were operated duringSAMUM 2006 in southern Morocco to measure height profiles of the volume extinction coefficient, the extinction-to-backscatter ratio and the depolarization ratio of dust particles in the Saharan dust layer at several wavelengths. Aerosol Robotic Network (AERONET) Sun photometer observations and radiosoundings of meteorological parameters complemented the ground-based activities at the SAMUM station of Ouarzazate. Four case studies are presented. Two case studies deal with the comparison of observations of the three ground-based lidars during a heavy dust outbreak and of the ground-based lidars with the airborne lidar. Two further cases show profile observations during satellite overpasses on 19 May and 4 June 2006. The height resolved statistical analysis reveals that the dust layer top typically reaches 4–6 km height above sea level (a.s.l.), sometimes even 7 km a.s.l.. Usually, a vertically inhomogeneous dust plume with internal dust layers was observed in the morning before the evolution of the boundary layer started. The Saharan dust layer was well mixed in the early evening. The 500 nm dust optical depth ranged from 0.2–0.8 at the field site south of the High Atlas mountains, Ångström exponents derived from photometer and lidar data were between 0–0.4. The volume extinction coefficients (355, 532 nm) varied from 30–300Mm−1 with a mean value of 100Mm−1 in the lowest 4 km a.s.l.. On average, extinction-to-backscatter ratios of 53–55 sr (±7–13 sr) were obtained at 355, 532 and 1064 nm.
- ItemCharacterization of the planetary boundary layer during SAMUM-2 by means of lidar measurements(Milton Park : Taylor & Francis, 2017) Groß, Silke; Gasteiger, Josef; Freudenthaler, Volker; Wiegner, Matthias; Geiß, Alexander; Schladitz, Alexander; Toledano, Carlos; Kandler, Konrad; Tesche, Matthias; Ansmann, Albert; Wiedensohler, AlfredMeasurements with two Raman-depolarization lidars of the Meteorological Institute of the Ludwig-Maximilians- Universit¨at, M¨unchen, Germany, performed during SAMUM-2, were used to characterize the planetary boundary layer (PBL) over Praia, Cape Verde. A novel approach was used to determine the volume fraction of dust υd in the PBL. This approach primarily relies on accurate measurements of the linear depolarization ratio. Comparisons with independent in situ measurements showed the reliability of this approach. Based on our retrievals, two different phases could be distinguished within the measurement period of almost one month. The first (22–31 January 2008) was characterized by high aerosol optical depth (AOD) in the PBL and large υd > 95%. During the second phase, the AOD in the PBL was considerably lower and υd less than ∼40%. These findings were in very good agreement with ground based in situ measurements, when ambient volume fractions are considered that were calculated from the actual measurements of the dry volume fraction. Only in cases when dust was not the dominating aerosol component (second phase), effects due to hygroscopic growth became important.
- ItemOptical and microphysical properties of smoke over Cape Verde inferred from multiwavelength lidar measurements(Milton Park : Taylor & Francis, 2017) Tesche, Matthias; Müller, Detlef; Gross, Silke; Ansmann, Albert; Althausen, Dietrich; Freudenthaler, Volker; Weinzierl, Bernadett; Veira, Andreas; Petzold, AndreasLidar measurements of mixed dust/smoke plumes over the tropical Atlantic ocean were carried out during the winter campaign of SAMUM-2 at Cape Verde. Profiles of backscatter and extinction coefficients, lidar ratios, and Ångstr¨om exponents related to pure biomass-burning aerosol from southern West Africa were extracted from these observations. Furthermore, these findings were used as input for an inversion algorithm to retrieve microphysical properties of pure smoke. Seven measurement days were found suitable for the procedure of aerosol-type separation and successive inversion of optical data that describe biomass-burning smoke. We inferred high smoke lidar ratios of 87 ± 17 sr at 355 nm and 79 ± 17 sr at 532 nm. Smoke lidar ratios and Ångstr¨om exponents are higher compared to the ones for the dust/smoke mixture. These numbers indicate higher absorption and smaller sizes for pure smoke particles compared to the dust/smoke mixture. Inversion of the smoke data set results in mean effective radii of 0.22 ± 0.08 μm with individual results varying between 0.10 and 0.36 μm. The single-scattering albedo for pure biomass-burning smoke was found to vary between 0.63 and 0.89 with a very low mean value of 0.75 ± 0.07. This is in good agreement with findings of airborne in situ measurements which showed values of 0.77 ± 0.03. Effective radii from the inversion were similar to the ones found for the fine mode of the in situ size distributions.
- ItemVertically resolved dust optical properties during SAMUM: Tinfou compared to Ouarzazate(Milton Park : Taylor & Francis, 2017) Heese, Birgit; Althausen, Dietrich; Dinter, Tilman; Esselborn, Michael; Müller, Thomas; Tesche, Matthias; Wiegner, MatthiasVertical profiles of dust key optical properties are presented from measurements during the Saharan Mineral Dust Experiment (SAMUM) by Raman and depolarization lidar at two ground-based sites and by airborne high spectral resolution lidar. One of the sites, Tinfou, is located close to the border of the Sahara in Southern Morocco and was the main in situ site during SAMUM. The other site was Ouarzazate airport, the main lidar site. From the lidar measurements the spatial distribution of the dust between Tinfou and Ouarzazate was derived for 1 d. The retrieved profiles of backscatter and extinction coefficients and particle depolarization ratios show comparable dust optical properties, a similar vertical structure of the dust layer, and a height of about 4 km asl at both sites. The airborne cross-section of the extinction coefficient at the two sites confirms the low variability in dust properties. Although the general picture of the dust layer was similar, the lidar measurements reveal a higher dust load closer to the dust source. Nevertheless, the observed intensive optical properties were the same. These results indicate that the lidar measurements at two sites close to the dust source are both representative for the SAMUM dust conditions.
- ItemSpatial distribution and optical properties of Saharan dust observed by airborne high spectral resolution lidar during SAMUM 2006(Milton Park : Taylor & Francis, 2017) Esselborn, Michael; Wirth, Martin; Fix, Andreas; Weinzierl, Bernadett; Rasp, Katharina; Tesche, Matthias; Petzold, AndreasAirborne measurements of pure Saharan dust extinction and backscatter coefficients, the corresponding lidar ratio and the aerosol optical thickness (AOT) have been performed during the Saharan Mineral Dust Experiment 2006, with a high spectral resolution lidar. Dust layers were found to range from ground up to 4–6 km above sea level (asl). Maximum AOT values at 532 nm, encountered within these layers during the DLR Falcon research flights were 0.50–0.55. A significant horizontal variability of the AOT south of the High Atlas mountain range was observed even in cases of a well-mixed dust layer. High vertical variations of the dust lidar ratio of 38–50 sr were observed in cases of stratified dust layers. The variability of the lidar ratio was attributed to dust advection from different source regions. The aerosol depolarization ratio was about 30% at 532 nm during all measurements and showed only marginal vertical variations.
- ItemMeasurement report: Balloon-borne in situ profiling of Saharan dust over Cyprus with the UCASS optical particle counter(Katlenburg-Lindau : European Geosciences Union, 2021) Kezoudi, Maria; Tesche, Matthias; Smith, Helen; Tsekeri, Alexandra; Baars, Holger; Dollner, Maximilian; Estellés, VÃctor; Bühl, Johannes; Weinzierl, Bernadett; Ulanowski, Zbigniew; Müller, Detlef; Amiridis, VassilisThis paper presents measurements of mineral dust concentration in the diameter range from 0.4 to 14.0 µm with a novel balloon-borne optical particle counter, the Universal Cloud and Aerosol Sounding System (UCASS). The balloon launches were coordinated with ground-based active and passive remote-sensing observations and airborne in situ measurements with a research aircraft during a Saharan dust outbreak over Cyprus from 20 to 23 April 2017. The aerosol optical depth at 500 nm reached values up to 0.5 during that event over Cyprus, and particle number concentrations were as high as 50 cm−3 for the diameter range between 0.8 and 13.9 µm. Comparisons of the total particle number concentration and the particle size distribution from two cases of balloon-borne measurements with aircraft observations show reasonable agreement in magnitude and shape despite slight mismatches in time and space. While column-integrated size distributions from balloon-borne measurements and ground-based remote sensing show similar coarse-mode peak concentrations and diameters, they illustrate the ambiguity related to the missing vertical information in passive sun photometer observations. Extinction coefficient inferred from the balloon-borne measurements agrees with those derived from coinciding Raman lidar observations at height levels with particle number concentrations smaller than 10 cm−3 for the diameter range from 0.8 to 13.9 µm. An overestimation of the UCASS-derived extinction coefficient of a factor of 2 compared to the lidar measurement was found for layers with particle number concentrations that exceed 25 cm−3, i.e. in the centre of the dust plume where particle concentrations were highest. This is likely the result of a variation in the refractive index and the shape and size dependency of the extinction efficiency of dust particles along the UCASS measurements. In the future, profile measurements of the particle number concentration and particle size distribution with the UCASS could provide a valuable addition to the measurement capabilities generally used in field experiments that are focussed on the observation of coarse aerosols and clouds.
- ItemDust mobilization and transport in the northern Sahara during SAMUM 2006 - A meteorological overview(Milton Park : Taylor & Francis, 2017) Knippertz, Peter; Ansmann, Albert; Althausen, Dietrich; Müller, Detlef; Tesche, Matthias; Bierwirth, Eike; Dinter, Tilman; Müller, Thomas; Von Hoyningen-Huene, Wolfgang; Schepanski, Kerstin; Wendisch, Manfred; Heinold, Bernd; Kandler, Konrad; Petzold, Andreas; Tegen, InaThe SAMUM field campaign in southern Morocco in May/June 2006 provides valuable data to study the emission, and the horizontal and vertical transports of mineral dust in the Northern Sahara. Radiosonde and lidar observations show differential advection of air masses with different characteristics during stable nighttime conditions and up to 5-km deep vertical mixing in the strongly convective boundary layer during the day. Lagrangian and synoptic analyses of selected dust periods point to a topographic channel from western Tunisia to central Algeria as a dust source region. Significant emission events are related to cold surges from the Mediterranean in association with eastward passing upper-level waves and lee cyclogeneses south of the Atlas Mountains. Other relevant events are local emissions under a distinct cut-off low over northwestern Africa and gust fronts associated with dry thunderstorms over the Malian and Algerian Sahara. The latter are badly represented in analyses from the European Centre for Medium–Range Weather Forecasts and in a regional dust model, most likely due to problems with moist convective dynamics and a lack of observations in this region. This aspect needs further study. The meteorological source identification is consistent with estimates of optical and mineralogical properties of dust samples.
- ItemProfiling of Saharan dust and biomass-burning smoke with multiwavelength polarization Raman lidar at Cape Verde(Milton Park : Taylor & Francis, 2017) Tesche, Matthias; Gross, Silke; Ansmann, Albert; Müller, Detlef; Althausen, Dietrich; Freudenthaler, Volker; Esselborn, MichaelExtensive lidar measurements of Saharan dust and biomass-burning smoke were performed with one airborne and three ground-based instruments in the framework of the second part of the SAharan Mineral dUst experiMent (SAMUM-2a) during January and February of 2008 at Cape Verde. Further lidar observations with one system only were conducted duringMay and June of 2008 (SAMUM-2b). The active measurements were supported by Sun photometer observations. During winter, layers of mineral dust from the Sahara and biomass-burning smoke from southern West Africa pass Cape Verde on their way to South America while pure dust layers cross the Atlantic on their way to the Caribbean during summer. The mean 500-nm aerosol optical thickness (AOT) observed during SAMUM-2a was 0.35 ± 0.18. SAMUM-2a observations showed transport of pure dust within the lowermost 1.5 km of the atmospheric column. In the height range from 1.5 to 5.0 km, mixed dust/smoke layers with mean lidar ratios of 67 ± 14 sr at 355 and 532 nm, respectively, prevailed. Within these layers, wavelength-independent linear particle depolarization ratios of 0.12–0.18 at 355, 532, and 710 nm indicate a large contribution (30–70%) of mineral dust to the measured optical properties. Ångstr¨om exponents for backscatter and extinction of around 0.7 support this finding. Mean extinction coefficients in the height range between 2 and 4 km were 66 ± 6 Mm−1 at 355 nm and 48 ± 5 Mm−1 at 532 nm. Comparisons with airborne high-spectral-resolution lidar observations show good agreement within the elevated layers. 3–5 km deep dust layers where observed during SAMUM-2b. These layers showed optical properties similar to the ones of SAMUM-1 in Morocco with a mean 500-nm AOT of 0.4 ± 0.2. Dust extinction coefficients were about 80 ± 6 Mm−1 at 355 and 532 nm. Dust lidar ratios were 53 ± 10 sr at 355 and 532 nm, respectively. Dust depolarization ratios showed an increase with wavelength from 0.31 ± 0.10 at 532 nm to 0.37 ± 0.07 at 710 nm.