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Author: Althausen, Dietrich × Author: Weinzierl, Bernadett × End date: 2019 × Start date: 2010 × Type: article × Subject: dust ×

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    Optical 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, 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.
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    Regional Saharan dust modelling during the SAMUM 2006 campaign
    (Milton Park : Taylor & Francis, 2017) Heinold, Bernd; Tegen, Ina; Esselborn, Michael; Kandler, Konrad; Knippertz, Peter; Müller, Detlef; Schladitz, Alexander; Tesche, Matthias; Weinzierl, Bernadett; Ansmann, Albert; Althausen, Dietrich; Laurent, Benoit; Massling, Andreas; Müller, Thomas; Petzold, Andreas; Schepanski, Kerstin; Wiedensohler, Alfred
    The regional dust model system LM-MUSCAT-DES was developed in the framework of the SAMUM project. Using the unique comprehensive data set of near-source dust properties during the 2006SAMUMfield campaign, the performance of the model system is evaluated for two time periods in May and June 2006. Dust optical thicknesses, number size distributions and the position of the maximum dust extinction in the vertical profiles agree well with the observations. However, the spatio-temporal evolution of the dust plumes is not always reproduced due to inaccuracies in the dust source placement by the model. While simulated winds and dust distributions are well matched for dust events caused by dry synoptic-scale dynamics, they are often misrepresented when dust emissions are caused by moist convection or influenced by small-scale topography that is not resolved by the model. In contrast to long-range dust transport, in the vicinity of source regions the model performance strongly depends on the correct prediction of the exact location of sources. Insufficiently resolved vertical grid spacing causes the absence of inversions in the model vertical profiles and likely explains the absence of the observed sharply defined dust layers.
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    Regional modelling of Saharan dust and biomass-burning smoke, Part I: Model description and evaluation
    (Milton Park : Taylor & Francis, 2017) Heinold, Bernd; Tegen, Ina; Schepanski, Kerstin; Tesche, Matthias; Esselborn, Michael; Freudenthaler, Volker; Gross, Silke; Kandler, Konrad; Knippertz, Peter; Müller, Detlef; Schladitz, Alexander; Toledano, Carlos; Weinzierl, Bernadett; Ansmann, Albert; Althausen, Dietrich; Müller, Thomas; Petzold, Andreas; Wiedensohler, Alfred
    The spatio-temporal evolution of the Saharan dust and biomass-burning plume during the SAMUM-2 field campaign in January and February 2008 is simulated at 28 km horizontal resolution with the regional model-system COSMOMUSCAT. The model performance is thoroughly tested using routine ground-based and space-borne remote sensing and local field measurements. Good agreement with the observations is found in many cases regarding transport patterns, aerosol optical thicknesses and the ratio of dust to smoke aerosol. The model also captures major features of the complex aerosol layering. Nevertheless, discrepancies in the modelled aerosol distribution occur, which are analysed in detail. The dry synoptic dynamics controlling dust uplift and transport during the dry season are well described by the model, but surface wind peaks associated with the breakdown of nocturnal low-level jets are not always reproduced. Thus, a strong dust outbreak is underestimated. While dust emission modelling is a priori more challenging, since strength and placement of dust sources depend on on-line computed winds, considerable inaccuracies also arise in observation-based estimates of biomass-burning emissions. They are caused by cloud and spatial errors of satellite fire products and uncertainties in fire emission parameters, and can lead to unrealistic model results of smoke transport.