Filters

20172

More filters

20192
Reset filters

Settings

Author: Ansmann, Albert × Author: Freudenthaler, Volker × Author: Groß, Silke × Type: article × Subject: lidar ×

Search Results

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    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
    (Milton Park : Taylor & Francis, 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.
  • Thumbnail Image
    Item
    Characterization 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, Alfred
    Measurements 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.