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Optical and microphysical properties of smoke over Cape Verde inferred from multiwavelength lidar measurements
2017, Tesche, Matthias, Müller, Detlef, Gross, Silke, Ansmann, Albert, Althausen, Dietrich, Freudenthaler, Volker, Weinzierl, Bernadett, Veira, Andreas, Petzold, Andreas
Lidar 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.
Microphysical and optical properties of dust and tropical biomass burning aerosol layers in the Cape Verde region - an overview of the airborne in situ and lidar measurements during SAMUM-2
2017, Weinzierl, Bernadett, Sauer, Daniel, Esselborn, Michael, Petzold, Andreas, Veira, Andreas, Rose, Maximilian, Mund, Susanne, Wirth, Martin, Ansmann, Albert, Tesche, Matthias, Gross, Silke, Freudenthaler, Volker
In the framework of the Saharan Mineral Dust Experiment (SAMUM) airborne High Spectral Resolution Lidar and in situ measurements of the particle size, aerosol mixing state and absorption coefficient were conducted. Here, the properties of mineral dust and tropical biomass burning layers in the Cape Verde region in January/February 2008 are investigated and compared with the properties of fresh dust observed in May/June 2006 close the Sahara. In the Cape Verde area, we found a complex stratification with dust layers covering the altitude range below 2 km and biomass burning layers aloft. The aerosol type of the individual layers was classified based on depolarization and lidar ratios and, in addition, on in situ measured Ångström exponents of absorption åap. The dust layers had a depth of 1.3 ± 0.4 km and showed a median åap of 3.95. The median effective diameter Deff was 2.5 μm and the dust layers over Cape Verde yielded clear signals of aging: large particles were depleted due to gravitational settling and the accumulation mode diameter was shifted towards larger sizes as a result of coagulation. The tropical biomass layers had a depth of 2.0 ± 1.1 km and were characterized by a median åap of 1.34. They always contained a certain amount of large dust particles and showed a median Deff of 1.1 μm and a fine mode Deff,fine of 0.33. The dust and biomass burning layers had a median aerosol optical depth (AOD) of 0.23 and 0.09, respectively. The median contributions to the AOD of the total atmospheric column below 10 km were 75 and 37%, respectively.
Characterization 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
2017, Groß, Silke, Tesche, Matthias, Freudenthaler, Volker, Toledano, Carlos, Wiegner, Matthias, Ansmann, Albert, Althausen, Dietrich, Seefeldner, Meinhard
The 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.