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- ItemOptical properties of long-range transported Saharan dust over Barbados as measured by dual-wavelength depolarization Raman lidar measurements(München : European Geopyhsical Union, 2015) Groß, S.; Freudenthaler, V.; Schepanski, K.; Toledano, C.; Schäfler, A.; Ansmann, A.; Weinzierl, B.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.
- ItemCeilometer lidar comparison: Backscatter coefficient retrieval and signal-to-noise ratio determination(München : European Geopyhsical Union, 2010) Heese, B.; Flentje, H.; Althausen, D.; Ansmann, A.; Frey, S.The potential of a new generation of ceilometer instruments for aerosol monitoring has been studied in the Ceilometer Lidar Comparison (CLIC) study. The used ceilometer was developed by Jenoptik, Germany, and is designed to find both thin cirrus clouds at tropopause level and aerosol layers at close ranges during day and night-time. The comparison study was performed to determine up to which altitude the ceilometers are capable to deliver particle backscatter coefficient profiles. For this, the derived ceilometer profiles are compared to simultaneously measured lidar profiles at the same wavelength. The lidar used for the comparison was the multi-wavelengths Raman lidar PollyXT. To demonstrate the capabilities and limits of ceilometers for the derivation of particle backscatter coefficient profiles from their measurements two examples of the comparison results are shown. Two cases, a daytime case with high background noise and a less noisy night-time case, are chosen. In both cases the ceilometer profiles compare well with the lidar profiles in atmospheric structures like aerosol layers or the boundary layer top height. However, the determination of the correct magnitude of the particle backscatter coefficient needs a calibration of the ceilometer data with an independent measurement of the aerosol optical depth by a sun photometer. To characterizes the ceilometers signal performance with increasing altitude a comprehensive signal-to-noise ratio study was performed. During daytime the signal-to-noise ratio is higher than 1 up to 4–5 km depending on the aerosol content. In our night-time case the SNR is higher than 1 even up to 8.5 km, so that also aerosol layers in the upper troposphere had been detected by the ceilometer.
- 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.
- ItemOptical and geometrical aerosol particle properties over the United Arab Emirates(Katlenburg-Lindau : EGU, 2020) Filioglou, Maria; Giannakaki, Elina; Backman, John; Kesti, Jutta; Hirsikko, Anne; Engelmann, Ronny; O’Connor, Ewan; Leskinen, Jari T.T.; Shang, Xiaoxia; Korhonen, Hannele; Lihavainen, Heikki; Romakkaniemi, Sami; Komppula, MikaOne year of ground-based night-time Raman lidar observations has been analysed under the Optimization of Aerosol Seeding In rain enhancement Strategies (OASIS) project, in order to characterize the aerosol particle properties over a rural site in the United Arab Emirates. In total, 1130 aerosol particle layers were detected during the 1-year measurement campaign which took place between March 2018 and February 2019. Several subsequent aerosol layers could be observed simultaneously in the atmosphere up to 11 km. The observations indicate that the measurement site is a receptor of frequent dust events, but predominantly the dust is mixed with aerosols of anthropogenic and/or marine origin. The mean aerosol optical depth over the measurement site ranged at 0.37±0.12 and 0.21±0.11 for 355 and 532 nm, respectively. Moreover, mean lidar ratios of 43±11 sr at a wavelength of 355 nm and 39±10 sr at 532 nm were found. The average linear particle depolarization ratio measured over the course of the campaign was 15±6% and 19±7% at the 355 and 532 nm wavelengths, respectively. Since the region is both a source and a receptor of mineral dust, we have also explored the properties of Arabian mineral dust of the greater area of the United Arab of Emirates and the Arabian Peninsula. The observed Arabian dust particle properties were 45±5 (42±5) sr at 355 (532) nm for the lidar ratio, 25±2% (31±2 %) for the linear particle depolarization ratio at 355 (532) nm, and 0.3±0.2 (0.2±0.2) for the extinction-related Angstrom exponent (backscatterrelated Angstrom exponent) between 355 and 532 nm. This study is the first to report comprehensive optical properties of the Arabian dust particles based on 1-year long observations, using to their fullest the capabilities of a multi-wavelength Raman lidar instrument. The results suggest that the mineral dust properties over the Middle East and western Asia, including the observation site, are comparable to those of African mineral dust with regard to the particle depolarization ratios, but not for lidar ratios. The smaller lidar ratio values in this study compared to the reference studies are attributed to the difference in the geochemical characteristics of the soil originating in the study region compared to northern Africa. © 2020 Royal Society of Chemistry. All rights reserved.
- ItemContinuous vertical aerosol profiling with a multi-wavelength Raman polarization lidar over the Pearl River Delta, China(Katlenburg-Lindau : EGU, 2017) Heese, Birgit; Baars, Holger; Bohlmann, Stephanie; Althausen, Dietrich; Deng, RuruA dataset of particle optical properties of the highly polluted atmosphere over the Pearl River Delta (PRD), Guangzhou, China, is presented in this paper. The data were derived from the measurements of a multiwavelength Raman and depolarization lidar PollyXT and a co-located AERONET sun photometer. The measurement campaign was conducted from November 2011 to mid-June 2012. These are the first Raman lidar measurements in the PRD that lasted for several months. A mean value of aerosol optical depth (AOD) of 0.54±0.33 was observed by the sun photometer at 500 nm in the polluted atmosphere over this megacity for the whole measurement period. The lidar profiles frequently show lofted aerosol layers, which reach altitudes of up to 2 to 3 km and, especially during the spring season, up to 5 km. These layers contain between 12 and 56% of the total AOD, with the highest values in spring. The aerosol types in these lofted layers are classified by their optical properties. The observed lidar ratio values range from 30 to 80 sr with a mean value of 48.0±10.7 sr at 532 nm. The linear particle depolarization ratio at 532 nm lies mostly below 5 %, with a mean value of 3.6±3.7 %. The majority of the Ångström exponents lie between 0.5 and 1.5, indicating a mixture of fine- and coarsemode aerosols. These results reveal that mostly urban pollution particles mixed with particles produced from biomass and industrial burning are present in the atmosphere above the Pearl River Delta. Trajectory analyses show that these pollution mixtures arise mainly from local and regional sources.